PostgreSQL源代码分析：indxpath.c
建议在阅读本文时，结合《PostgreSQL技术内幕：查询优化深度探索》（张树杰著）的第六章。
索引到底可以在哪些场景中被使用？
借助索引，可以实现索引扫描、IndexOnly Scan、位图扫描、索引连接（参数化路径）。从下文的源代码中可以看出，如果一个查询想要使用索引，则查询必须满足下面4个条件之一：
- 查询条件中的列与索引列相匹配。比如表在a列上有一个btree索引，则where a=10可以使用这个索引。
-
查询条件被部分索引的谓词的条件所蕴含。比如表上有一个部分索引，索引了所有a>10的数据，则where a>10所查询的数据一定在索引中存在，此时，可以通过使用索引过滤到一些明显不满足要求的行（a<=10的行）。
-
Index Only Scan。此时可以避免对不需要的列进行投影，节省IO。
-
索引可以满足查询的排序要求。如果查询中有order by，并且索引可以按顺序返回数据，则可以通过使用索引避免对数据进行排序。
SAOP是什么？
SAOP的全称是ScalarArrayOpExpr，可以把它简单理解成数组，常在in和any子句中出现，比如 a in (1,1,1,2,3,4,5)、a = any(array[1,2,3])等。在src/test/modules/test_predtest/sql/test_predtest.sql中搜索ScalarArrayOpExpr可以看到更多相关测试用例。
PG使用这个结构，把处理数组的操作直接下推到具体索引中。比如，PG可以直接把 a in (1,1,1,2,3,4,5)这个条件一次性传给btree，btree索引将对数组进行排序、去重，迭代这个数组，依次返回每个符合条件的结果。如果不把这个数组下推给btree，则执行器需要完成去重再依次将每个值传给btree，等btree对一个值完成扫描后，执行器再将下一个值传递给btree。
目前只有btree支持ScalarArrayOpExpr，一旦出现ScalarArrayOpExpr，基本都与btree相关。
Index Cond和Filter
观察下面的查询计划，可以发现，a=1和b=1的位置不同，二者的位置不同，作用也不同。索引扫描过程中，使用a=1去索引中查找对应行的ctid，再到heap中找出整行数据，最后对这行数据使用b=1进行过滤。当满足b=1时，才将这行数据返回。
create table t(a int, b int);
create index on t(a);
set enable_seqscan = 0;
set enable_bitmapscan=0;
explain select * from t where a=1 and b=1;
QUERY PLAN
------------------------------------------------------------------
Index Scan using t_a_idx on t (cost=0.15..36.38 rows=1 width=8)
Index Cond: (a = 1)
Filter: (b = 1)
(3 rows)
生成索引路径时，最好能够把条件放在Index Cond中，这样可以使用这个条件在索引中查找数据，避免使用ctid到heap中获取数据后再将数据淘汰。本例中，索引中不包含b列，因此无法将b=1放在Index Cond中。
版本号
本次注释使用的版本为(PostgreSQL) 14devel，git仓库的commit id如下：
$ git log
commit 32d6287d2eef6b6a4dde07e0513f3e4f321792ad (HEAD -> master, origin/master, origin/HEAD)
Author: Peter Geoghegan <pg@bowt.ie>
Date: Wed Dec 30 17:21:42 2020 -0800
Get heap page max offset with buffer lock held.
On further reflection it seems better to call PageGetMaxOffsetNumber()
after acquiring a buffer lock on the page. This shouldn't really
matter, but doing it this way is cleaner.
Follow-up to commit 42288174.
Backpatch: 12-, just like commit 42288174
下面的代码是完整的indxpath.c文件，读者可以直接用它替换32d6287d2中的indxpath.c，进行编译。
Github仓库
本文中的代码已经托管到了github，本文所添加的注释可参考下面的commit：
https://github.com/mengqingzhong/postgres/commit/807058bf9a93240eb29fcd7dab22d7527ffa8547
/*-------------------------------------------------------------------------
*
* indxpath.c
* Routines to determine which indexes are usable for scanning a
* given relation, and create Paths accordingly.
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/optimizer/path/indxpath.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <math.h>
#include "access/stratnum.h"
#include "access/sysattr.h"
#include "catalog/pg_am.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_type.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/supportnodes.h"
#include "optimizer/cost.h"
#include "optimizer/optimizer.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/prep.h"
#include "optimizer/restrictinfo.h"
#include "utils/lsyscache.h"
#include "utils/selfuncs.h"
/*
* 比较列的collation是否相同。collation指的是排序规则，不是PostgreSQL独有的概念，
* 同样一堆字符，在不同的排序规则下顺序可能不同。详情可以查阅其它资料。
*/
/* XXX see PartCollMatchesExprColl */
#define IndexCollMatchesExprColl(idxcollation, exprcollation) \
((idxcollation) == InvalidOid || (idxcollation) == (exprcollation))
/*
* 我们想生成索引扫描，还是位图扫描，还是任意一个都可以呢？
* 从下面的代码来看，只使用了ST_BITMAPSCAN和ST_ANYSCAN，并没有使用ST_INDEXSCAN。
* 在某些场景下，我们只想得到一个位图，因此使用ST_BITMAPSCAN标记
*/
/* Whether we are looking for plain indexscan, bitmap scan, or either */
typedef enum
{
ST_INDEXSCAN, /* must support amgettuple */
ST_BITMAPSCAN, /* must support amgetbitmap */
ST_ANYSCAN /* either is okay */
} ScanTypeControl;
/*
* 处理查询语句中的各种条件是本文件最复杂的工作之一。
* 在下面的处理中，经常需要把一系列条件与索引中的列进行匹配。这些条件按索引列进行组织，
* 即与同一个索引列匹配成功的所有条件，都被放在同一个List中。
* 因为一个索引最多有INDEX_MAX_KEYS个列，所以List数组的大小为INDEX_MAX_KEYS。
* 如果IndexClauseSet的List中没有任何条件，则nonempty为false；否则为true。这可以在某些场景下加速判断。
*/
/* Data structure for collecting qual clauses that match an index */
typedef struct
{
bool nonempty; /* True if lists are not all empty */
/* Lists of IndexClause nodes, one list per index column */
List *indexclauses[INDEX_MAX_KEYS];
} IndexClauseSet;
/*
* 在生成位图扫描路径时，需要在多个路径中选择一个子集，并且把子集中的路径AND起来。
* 选择最优子集算法的时间复杂度是指数级，PG使用了一些启发式规则，将时间复杂度降低到O(N^2)。
* 在应用这些启发式规则过程中，需要对路径进行排序，PathClauseUsage在排序过程中被使用，
* 它记录了每条路径上的一些信息。
*/
/* Per-path data used within choose_bitmap_and() */
typedef struct
{
Path *path; /* IndexPath, BitmapAndPath, or BitmapOrPath */
List *quals; /* the WHERE clauses it uses */
List *preds; /* predicates of its partial index(es) */
Bitmapset *clauseids; /* quals+preds represented as a bitmapset */
bool unclassifiable; /* has too many quals+preds to process? */
} PathClauseUsage;
/*
* PG在生成参数化路径过程中，会根据等价类推导出一些新的连接条件，这由generate_implied_equalities_for_column完成，
* 这个函数需要一个回调函数，在本文件中回调函数是ec_member_matches_indexcol，ec_member_matches_arg是
* ec_member_matches_indexcol的一个参数。
*/
/* Callback argument for ec_member_matches_indexcol */
typedef struct
{
IndexOptInfo *index; /* index we're considering */
int indexcol; /* index column we want to match to */
} ec_member_matches_arg;
static void consider_index_join_clauses(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index,
IndexClauseSet *rclauseset,
IndexClauseSet *jclauseset,
IndexClauseSet *eclauseset,
List **bitindexpaths);
static void consider_index_join_outer_rels(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index,
IndexClauseSet *rclauseset,
IndexClauseSet *jclauseset,
IndexClauseSet *eclauseset,
List **bitindexpaths,
List *indexjoinclauses,
int considered_clauses,
List **considered_relids);
static void get_join_index_paths(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index,
IndexClauseSet *rclauseset,
IndexClauseSet *jclauseset,
IndexClauseSet *eclauseset,
List **bitindexpaths,
Relids relids,
List **considered_relids);
static bool eclass_already_used(EquivalenceClass *parent_ec, Relids oldrelids,
List *indexjoinclauses);
static bool bms_equal_any(Relids relids, List *relids_list);
static void get_index_paths(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index, IndexClauseSet *clauses,
List **bitindexpaths);
static List *build_index_paths(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index, IndexClauseSet *clauses,
bool useful_predicate,
ScanTypeControl scantype,
bool *skip_nonnative_saop,
bool *skip_lower_saop);
static List *build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
List *clauses, List *other_clauses);
static List *generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
List *clauses, List *other_clauses);
static Path *choose_bitmap_and(PlannerInfo *root, RelOptInfo *rel,
List *paths);
static int path_usage_comparator(const void *a, const void *b);
static Cost bitmap_scan_cost_est(PlannerInfo *root, RelOptInfo *rel,
Path *ipath);
static Cost bitmap_and_cost_est(PlannerInfo *root, RelOptInfo *rel,
List *paths);
static PathClauseUsage *classify_index_clause_usage(Path *path,
List **clauselist);
static void find_indexpath_quals(Path *bitmapqual, List **quals, List **preds);
static int find_list_position(Node *node, List **nodelist);
static bool check_index_only(RelOptInfo *rel, IndexOptInfo *index);
static double get_loop_count(PlannerInfo *root, Index cur_relid, Relids outer_relids);
static double adjust_rowcount_for_semijoins(PlannerInfo *root,
Index cur_relid,
Index outer_relid,
double rowcount);
static double approximate_joinrel_size(PlannerInfo *root, Relids relids);
static void match_restriction_clauses_to_index(PlannerInfo *root,
IndexOptInfo *index,
IndexClauseSet *clauseset);
static void match_join_clauses_to_index(PlannerInfo *root,
RelOptInfo *rel, IndexOptInfo *index,
IndexClauseSet *clauseset,
List **joinorclauses);
static void match_eclass_clauses_to_index(PlannerInfo *root,
IndexOptInfo *index,
IndexClauseSet *clauseset);
static void match_clauses_to_index(PlannerInfo *root,
List *clauses,
IndexOptInfo *index,
IndexClauseSet *clauseset);
static void match_clause_to_index(PlannerInfo *root,
RestrictInfo *rinfo,
IndexOptInfo *index,
IndexClauseSet *clauseset);
static IndexClause *match_clause_to_indexcol(PlannerInfo *root,
RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index);
static IndexClause *match_boolean_index_clause(RestrictInfo *rinfo,
int indexcol, IndexOptInfo *index);
static IndexClause *match_opclause_to_indexcol(PlannerInfo *root,
RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index);
static IndexClause *match_funcclause_to_indexcol(PlannerInfo *root,
RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index);
static IndexClause *get_index_clause_from_support(PlannerInfo *root,
RestrictInfo *rinfo,
Oid funcid,
int indexarg,
int indexcol,
IndexOptInfo *index);
static IndexClause *match_saopclause_to_indexcol(RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index);
static IndexClause *match_rowcompare_to_indexcol(RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index);
static IndexClause *expand_indexqual_rowcompare(RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index,
Oid expr_op,
bool var_on_left);
static void match_pathkeys_to_index(IndexOptInfo *index, List *pathkeys,
List **orderby_clauses_p,
List **clause_columns_p);
static Expr *match_clause_to_ordering_op(IndexOptInfo *index,
int indexcol, Expr *clause, Oid pk_opfamily);
static bool ec_member_matches_indexcol(PlannerInfo *root, RelOptInfo *rel,
EquivalenceClass *ec, EquivalenceMember *em,
void *arg);
/*
* create_index_paths()
* Generate all interesting index paths for the given relation.
* Candidate paths are added to the rel's pathlist (using add_path).
*
* To be considered for an index scan, an index must match one or more
* restriction clauses or join clauses from the query's qual condition,
* or match the query's ORDER BY condition, or have a predicate that
* matches the query's qual condition.
*
* There are two basic kinds of index scans. A "plain" index scan uses
* only restriction clauses (possibly none at all) in its indexqual,
* so it can be applied in any context. A "parameterized" index scan uses
* join clauses (plus restriction clauses, if available) in its indexqual.
* When joining such a scan to one of the relations supplying the other
* variables used in its indexqual, the parameterized scan must appear as
* the inner relation of a nestloop join; it can't be used on the outer side,
* nor in a merge or hash join. In that context, values for the other rels'
* attributes are available and fixed during any one scan of the indexpath.
*
* An IndexPath is generated and submitted to add_path() for each plain or
* parameterized index scan this routine deems potentially interesting for
* the current query.
*
* 'rel' is the relation for which we want to generate index paths
*
* Note: check_index_predicates() must have been run previously for this rel.
*
* Note: in cases involving LATERAL references in the relation's tlist, it's
* possible that rel->lateral_relids is nonempty. Currently, we include
* lateral_relids into the parameterization reported for each path, but don't
* take it into account otherwise. The fact that any such rels *must* be
* available as parameter sources perhaps should influence our choices of
* index quals ... but for now, it doesn't seem worth troubling over.
* In particular, comments below about "unparameterized" paths should be read
* as meaning "unparameterized so far as the indexquals are concerned".
*/
/*
* create_index_paths用来生成索引扫描路径，是本文件的入口函数。
*
* 如果想使用索引扫描，索引必须至少可以匹配一个过滤条件或连接条件，或者匹配查询的order by条件，
* 或者索引有一个谓词条件（部分索引）可以匹配查询中的条件.
*
* 基本的索引扫描有两种：plain和parameterized。
*
* 普通(plain)的索引扫描在indexqual（explain输出中的Index Cond）中只使用过滤条件（或者没有任何过滤条件，此时一定是IndexOnly Scan），
* 索引，它可以被用在任意上下文（指的是join的内外表）中。
*
* 参数化(parameterized)的索引扫描在indexqual中使用连接条件（也可能附加上过滤条件）。
* 当这样一个扫描路径和为它的indexqual提供参数的表进行join时，它必须是连接的内表，不能是外表（因为外表驱动内表，
* 为内表的扫描条件提供参数。反之，则不行）。这样的连接必须是Nestloop join，不能是merge join或hash join。
* 在这种场景下，每次外表扫描到新值时，都需要对内表的index scan调用rescan，以便将外表的参数传递给内表的index scan。
*/
void
create_index_paths(PlannerInfo *root, RelOptInfo *rel)
{
List *indexpaths;
List *bitindexpaths;
List *bitjoinpaths;
List *joinorclauses;
IndexClauseSet rclauseset;
IndexClauseSet jclauseset;
IndexClauseSet eclauseset;
ListCell *lc;
/* Skip the whole mess if no indexes */
if (rel->indexlist == NIL)
return;
/* Bitmap paths are collected and then dealt with at the end */
bitindexpaths = bitjoinpaths = joinorclauses = NIL;
/* 首先遍历表上的每个索引 */
/* Examine each index in turn */
foreach(lc, rel->indexlist)
{
IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
/* Protect limited-size array in IndexClauseSets */
Assert(index->nkeycolumns <= INDEX_MAX_KEYS);
/*
* Ignore partial indexes that do not match the query.
* (generate_bitmap_or_paths() might be able to do something with
* them, but that's of no concern here.)
*/
/*
* 如果这是一个部分索引，并且与查询不匹配，则忽略这个索引。
* 比如索引中仅包含a>10的数据，但是查询条件是a>0，则不能只用这个索引。
*/
if (index->indpred != NIL && !index->predOK)
continue;
/*
* Identify the restriction clauses that can match the index.
*/
/*
* 把过滤条件与索引进行匹配，匹配结果放在rclauseset中，参考上文IndexClauseSet中的注释。
*/
MemSet(&rclauseset, 0, sizeof(rclauseset));
match_restriction_clauses_to_index(root, index, &rclauseset);
/*
* Build index paths from the restriction clauses. These will be
* non-parameterized paths. Plain paths go directly to add_path(),
* bitmap paths are added to bitindexpaths to be handled below.
*/
/*
* 使用过滤条件生成索引扫描路径。这些都是非参数化路径。索引扫描、Index Only Scan的路径
* 可以用add_path添加到结果中；位图扫描的路径暂时先放在bitindexpaths中，
* 后面还要对这些位图扫描路径进行处理
*/
get_index_paths(root, rel, index, &rclauseset,
&bitindexpaths);
/*
* Identify the join clauses that can match the index. For the moment
* we keep them separate from the restriction clauses. Note that this
* step finds only "loose" join clauses that have not been merged into
* EquivalenceClasses. Also, collect join OR clauses for later.
*/
/*
* 把连接条件与索引进行匹配，匹配结果放在jclauseset中，参考上文IndexClauseSet中的注释。
* 这里匹配的连接条件，都还没有被merge到等价类中。
* OR类型的条件暂时被放在joinorclauses中，供后文用来生成OR类型的位图扫描。
*/
MemSet(&jclauseset, 0, sizeof(jclauseset));
match_join_clauses_to_index(root, rel, index,
&jclauseset, &joinorclauses);
/*
* Look for EquivalenceClasses that can generate joinclauses matching
* the index.
*/
/*
* 使用等价类推出新的连接条件，并把这些条件与索引进行匹配，匹配结果放在eclauseset中，
* 参考上文IndexClauseSet中的注释。
*/
MemSet(&eclauseset, 0, sizeof(eclauseset));
match_eclass_clauses_to_index(root, index,
&eclauseset);
/*
* 上面三处匹配，最终都调用了match_clause_to_index，只是外层对不同的连接列表进行迭代而已，
* 读者可以把三个函数进行对比，很容易就可以发现这一点。
*/
/*
* If we found any plain or eclass join clauses, build parameterized
* index paths using them.
*/
/* 如果最后两处匹配的结果非空，则尝试生成参数化路径 */
if (jclauseset.nonempty || eclauseset.nonempty)
consider_index_join_clauses(root, rel, index,
&rclauseset,
&jclauseset,
&eclauseset,
&bitjoinpaths);
}
/*
* PG在优化阶段，会对谓词条件进行拉平，也就是说，把所有条件放在一个列表中，这些条件的关系是AND。
* 列表中的单个条件，可能是一个OR类型的符合条件，比如整个列表可能表示a = 1 and (b = 1 or c =1)，
* (b = 1 or c =1)就是一个OR类型的符合条件。连接条件中的这种条件已经被保存在joinorclauses中。
* OR类型的条件在上面的路径生成过程中没有发挥任何作用，因此下面对这种类型的处理。
*
* 这是为什么这里只调用generate_bitmap_or_paths，并没有调用generate_bitmap_and_paths的原因。
*/
/*
* Generate BitmapOrPaths for any suitable OR-clauses present in the
* restriction list. Add these to bitindexpaths.
*/
indexpaths = generate_bitmap_or_paths(root, rel,
rel->baserestrictinfo, NIL);
bitindexpaths = list_concat(bitindexpaths, indexpaths);
/*
* Likewise, generate BitmapOrPaths for any suitable OR-clauses present in
* the joinclause list. Add these to bitjoinpaths.
*/
/*
* 把rel->baserestrictinfo作为other_rels传入generate_bitmap_or_paths可能得到更好的路径，
* 毕竟每多一个条件，就可能过滤掉更多的不满足条件的元组。
*/
indexpaths = generate_bitmap_or_paths(root, rel,
joinorclauses, rel->baserestrictinfo);
bitjoinpaths = list_concat(bitjoinpaths, indexpaths);
/*
* If we found anything usable, generate a BitmapHeapPath for the most
* promising combination of restriction bitmap index paths. Note there
* will be only one such path no matter how many indexes exist. This
* should be sufficient since there's basically only one figure of merit
* (total cost) for such a path.
*/
if (bitindexpaths != NIL)
{
Path *bitmapqual;
BitmapHeapPath *bpath;
/*
* 使用choose_bitmap_and在所有位图扫描路径中选出一个子集，对子集中的路径求AND，
* 生成最终的位图扫描路径。
*
* 这里生成的位图扫描路径是非参数化路径。
*/
bitmapqual = choose_bitmap_and(root, rel, bitindexpaths);
bpath = create_bitmap_heap_path(root, rel, bitmapqual,
rel->lateral_relids, 1.0, 0);
add_path(rel, (Path *) bpath);
/* create a partial bitmap heap path */
if (rel->consider_parallel && rel->lateral_relids == NULL)
create_partial_bitmap_paths(root, rel, bitmapqual);
}
/*
* 同理，生成参数化的位图扫描路径。为每种参数的组合生成一个位图扫描路径。
*/
/*
* Likewise, if we found anything usable, generate BitmapHeapPaths for the
* most promising combinations of join bitmap index paths. Our strategy
* is to generate one such path for each distinct parameterization seen
* among the available bitmap index paths. This may look pretty
* expensive, but usually there won't be very many distinct
* parameterizations. (This logic is quite similar to that in
* consider_index_join_clauses, but we're working with whole paths not
* individual clauses.)
*/
if (bitjoinpaths != NIL)
{
List *all_path_outers;
ListCell *lc;
/* Identify each distinct parameterization seen in bitjoinpaths */
/* 找出所有不同参数化方式的集合，两种不同的参数化方式使用的外表集合不同 */
all_path_outers = NIL;
foreach(lc, bitjoinpaths)
{
Path *path = (Path *) lfirst(lc);
Relids required_outer = PATH_REQ_OUTER(path);
/* 去重 */
if (!bms_equal_any(required_outer, all_path_outers))
all_path_outers = lappend(all_path_outers, required_outer);
}
/* Now, for each distinct parameterization set ... */
/* 对每种参数化方式进行下面的操作 */
foreach(lc, all_path_outers)
{
Relids max_outers = (Relids) lfirst(lc);
List *this_path_set;
Path *bitmapqual;
Relids required_outer;
double loop_count;
BitmapHeapPath *bpath;
ListCell *lcp;
/* Identify all the bitmap join paths needing no more than that */
/*
* 找出所有满足这种参数化方式的位图扫描路径。即找出所有需要的外表集合被max_outers
* 包含的那些位图扫描路径。假如max_outers为{t1, t2}，如果某个位图扫描路径P需要t3表为它
* 提供参数，则本次循环不能使用P。
*/
this_path_set = NIL;
foreach(lcp, bitjoinpaths)
{
Path *path = (Path *) lfirst(lcp);
if (bms_is_subset(PATH_REQ_OUTER(path), max_outers))
this_path_set = lappend(this_path_set, path);
}
/*
* Add in restriction bitmap paths, since they can be used
* together with any join paths.
*/
/*
* 把非参数化位图扫描路径也加进来，这可能会产生更好的结果。
* 这些路径不需要任何外表为它们提供参数，因此可以直接加进来。
*/
this_path_set = list_concat(this_path_set, bitindexpaths);
/* 同上，选出一个位图扫描路径的集合，把它们AND起来 */
/* Select best AND combination for this parameterization */
bitmapqual = choose_bitmap_and(root, rel, this_path_set);
/* And push that path into the mix */
required_outer = PATH_REQ_OUTER(bitmapqual);
/* 估算外表可以提供多少种不同的值，即这个位图扫描路径需要循环执行多少次。 */
loop_count = get_loop_count(root, rel->relid, required_outer);
bpath = create_bitmap_heap_path(root, rel, bitmapqual,
required_outer, loop_count, 0);
add_path(rel, (Path *) bpath);
}
}
}
/*
* 生成参数化路径使用的算法是：
* 1)首先确定一个外表集合S，这些外表集合为参数化路径提供参数
* 2)找出合适的条件，即排除使用除S之外的表为其提供参数的条件
*
* 尽量把这些条件放在indexqual上，而不是filter(qpqual)上。
*
* 这看起来算法复杂度很高，但是在实际中外表的组合方式不是很多。这里还使用了一种
* 启发式规则来限制外表的组合数量。
*/
/*
* 因为条件被匹配到索引的每个列上，所以需要对索引列进行迭代。
* consider_index_join_clauses函数的功能就是对索引列进行迭代，
* 然后调用consider_index_join_outer_rels
*/
/*
* consider_index_join_clauses
* Given sets of join clauses for an index, decide which parameterized
* index paths to build.
*
* Plain indexpaths are sent directly to add_path, while potential
* bitmap indexpaths are added to *bitindexpaths for later processing.
*
* 'rel' is the index's heap relation
* 'index' is the index for which we want to generate paths
* 'rclauseset' is the collection of indexable restriction clauses
* 'jclauseset' is the collection of indexable simple join clauses
* 'eclauseset' is the collection of indexable clauses from EquivalenceClasses
* '*bitindexpaths' is the list to add bitmap paths to
*/
static void
consider_index_join_clauses(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index,
IndexClauseSet *rclauseset,
IndexClauseSet *jclauseset,
IndexClauseSet *eclauseset,
List **bitindexpaths)
{
int considered_clauses = 0;
List *considered_relids = NIL;
int indexcol;
/*
* The strategy here is to identify every potentially useful set of outer
* rels that can provide indexable join clauses. For each such set,
* select all the join clauses available from those outer rels, add on all
* the indexable restriction clauses, and generate plain and/or bitmap
* index paths for that set of clauses. This is based on the assumption
* that it's always better to apply a clause as an indexqual than as a
* filter (qpqual); which is where an available clause would end up being
* applied if we omit it from the indexquals.
*
* This looks expensive, but in most practical cases there won't be very
* many distinct sets of outer rels to consider. As a safety valve when
* that's not true, we use a heuristic: limit the number of outer rel sets
* considered to a multiple of the number of clauses considered. (We'll
* always consider using each individual join clause, though.)
*
* For simplicity in selecting relevant clauses, we represent each set of
* outer rels as a maximum set of clause_relids --- that is, the indexed
* relation itself is also included in the relids set. considered_relids
* lists all relids sets we've already tried.
*/
for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)
{
/* Consider each applicable simple join clause */
considered_clauses += list_length(jclauseset->indexclauses[indexcol]);
consider_index_join_outer_rels(root, rel, index,
rclauseset, jclauseset, eclauseset,
bitindexpaths,
jclauseset->indexclauses[indexcol],
considered_clauses,
&considered_relids);
/* Consider each applicable eclass join clause */
considered_clauses += list_length(eclauseset->indexclauses[indexcol]);
consider_index_join_outer_rels(root, rel, index,
rclauseset, jclauseset, eclauseset,
bitindexpaths,
eclauseset->indexclauses[indexcol],
considered_clauses,
&considered_relids);
}
}
/*
* consider_index_join_outer_rels
* Generate parameterized paths based on clause relids in the clause list.
*
* Workhorse for consider_index_join_clauses; see notes therein for rationale.
*
* 'rel', 'index', 'rclauseset', 'jclauseset', 'eclauseset', and
* 'bitindexpaths' as above
* 'indexjoinclauses' is a list of IndexClauses for join clauses
* 'considered_clauses' is the total number of clauses considered (so far)
* '*considered_relids' is a list of all relids sets already considered
*/
/* 这个函数的主要作用就是生成不同的外表集合，然后调用get_join_index_paths */
static void
consider_index_join_outer_rels(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index,
IndexClauseSet *rclauseset,
IndexClauseSet *jclauseset,
IndexClauseSet *eclauseset,
List **bitindexpaths,
List *indexjoinclauses,
int considered_clauses,
List **considered_relids)
{
ListCell *lc;
/* Examine relids of each joinclause in the given list */
foreach(lc, indexjoinclauses)
{
IndexClause *iclause = (IndexClause *) lfirst(lc);
Relids clause_relids = iclause->rinfo->clause_relids;
EquivalenceClass *parent_ec = iclause->rinfo->parent_ec;
int num_considered_relids;
/* 已经考虑过这种外表的组合 */
/* If we already tried its relids set, no need to do so again */
if (bms_equal_any(clause_relids, *considered_relids))
continue;
/*
* Generate the union of this clause's relids set with each
* previously-tried set. This ensures we try this clause along with
* every interesting subset of previous clauses. However, to avoid
* exponential growth of planning time when there are many clauses,
* limit the number of relid sets accepted to 10 * considered_clauses.
*
* Note: get_join_index_paths appends entries to *considered_relids,
* but we do not need to visit such newly-added entries within this
* loop, so we don't use foreach() here. No real harm would be done
* if we did visit them, since the subset check would reject them; but
* it would waste some cycles.
*/
/*
* 下面尝试生成一种新的外表集合，并且使用这个集合调用get_join_index_paths
* 生成参数化路径
*/
num_considered_relids = list_length(*considered_relids);
for (int pos = 0; pos < num_considered_relids; pos++)
{
Relids oldrelids = (Relids) list_nth(*considered_relids, pos);
/*
* If either is a subset of the other, no new set is possible.
* This isn't a complete test for redundancy, but it's easy and
* cheap. get_join_index_paths will check more carefully if we
* already generated the same relids set.
*/
if (bms_subset_compare(clause_relids, oldrelids) != BMS_DIFFERENT)
continue;
/*
* If this clause was derived from an equivalence class, the
* clause list may contain other clauses derived from the same
* eclass. We should not consider that combining this clause with
* one of those clauses generates a usefully different
* parameterization; so skip if any clause derived from the same
* eclass would already have been included when using oldrelids.
*/
if (parent_ec &&
eclass_already_used(parent_ec, oldrelids,
indexjoinclauses))
continue;
/*
* If the number of relid sets considered exceeds our heuristic
* limit, stop considering combinations of clauses. We'll still
* consider the current clause alone, though (below this loop).
*/
if (list_length(*considered_relids) >= 10 * considered_clauses)
break;
/* OK, try the union set */
get_join_index_paths(root, rel, index,
rclauseset, jclauseset, eclauseset,
bitindexpaths,
bms_union(clause_relids, oldrelids),
considered_relids);
}
/* Also try this set of relids by itself */
/*
* 使用单个条件所涉及的外表集合。不用担心重复，
* 因为get_join_index_paths的开头会做精确的检查
*/
get_join_index_paths(root, rel, index,
rclauseset, jclauseset, eclauseset,
bitindexpaths,
clause_relids,
considered_relids);
}
}
/*
* get_join_index_paths
* Generate index paths using clauses from the specified outer relations.
* In addition to generating paths, relids is added to *considered_relids
* if not already present.
*
* Workhorse for consider_index_join_clauses; see notes therein for rationale.
*
* 'rel', 'index', 'rclauseset', 'jclauseset', 'eclauseset',
* 'bitindexpaths', 'considered_relids' as above
* 'relids' is the current set of relids to consider (the target rel plus
* one or more outer rels)
*/
/*
* 现在已经有了一个外表的集合S，这些外表为内表的参数化路径提供参数。
* 下面需要再次遍历（因为条件按索引列分组，因此需要再次按索引列遍历）每个条件，
* 把所有合适的条件（只要引用的外表被集合S包含就满足条件）找出来。
*/
static void
get_join_index_paths(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index,
IndexClauseSet *rclauseset,
IndexClauseSet *jclauseset,
IndexClauseSet *eclauseset,
List **bitindexpaths,
Relids relids,
List **considered_relids)
{
IndexClauseSet clauseset;
int indexcol;
/* If we already considered this relids set, don't repeat the work */
if (bms_equal_any(relids, *considered_relids))
return;
/* Identify indexclauses usable with this relids set */
MemSet(&clauseset, 0, sizeof(clauseset));
/*
* 遍历索引列上的每个条件，把所有合适的条件找出来
* 先找简单的连接条件，然后通过等价类生成的条件，最后把过滤条件加上。
* 因为过滤条件不依赖任何外表，因此可以直接加上。
*/
for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)
{
ListCell *lc;
/* First find applicable simple join clauses */
foreach(lc, jclauseset->indexclauses[indexcol])
{
IndexClause *iclause = (IndexClause *) lfirst(lc);
if (bms_is_subset(iclause->rinfo->clause_relids, relids))
clauseset.indexclauses[indexcol] =
lappend(clauseset.indexclauses[indexcol], iclause);
}
/*
* Add applicable eclass join clauses. The clauses generated for each
* column are redundant (cf generate_implied_equalities_for_column),
* so we need at most one. This is the only exception to the general
* rule of using all available index clauses.
*/
foreach(lc, eclauseset->indexclauses[indexcol])
{
IndexClause *iclause = (IndexClause *) lfirst(lc);
if (bms_is_subset(iclause->rinfo->clause_relids, relids))
{
clauseset.indexclauses[indexcol] =
lappend(clauseset.indexclauses[indexcol], iclause);
break;
}
}
/* Add restriction clauses */
clauseset.indexclauses[indexcol] =
list_concat(clauseset.indexclauses[indexcol],
rclauseset->indexclauses[indexcol]);
if (clauseset.indexclauses[indexcol] != NIL)
clauseset.nonempty = true;
}
/* We should have found something, else caller passed silly relids */
Assert(clauseset.nonempty);
/* 使用这些条件生成参数化路径 */
/* Build index path(s) using the collected set of clauses */
get_index_paths(root, rel, index, &clauseset, bitindexpaths);
/*
* Remember we considered paths for this set of relids.
*/
*considered_relids = lappend(*considered_relids, relids);
}
/*
* eclass_already_used
* True if any join clause usable with oldrelids was generated from
* the specified equivalence class.
*/
static bool
eclass_already_used(EquivalenceClass *parent_ec, Relids oldrelids,
List *indexjoinclauses)
{
ListCell *lc;
foreach(lc, indexjoinclauses)
{
IndexClause *iclause = (IndexClause *) lfirst(lc);
RestrictInfo *rinfo = iclause->rinfo;
if (rinfo->parent_ec == parent_ec &&
bms_is_subset(rinfo->clause_relids, oldrelids))
return true;
}
return false;
}
/*
* bms_equal_any
* True if relids is bms_equal to any member of relids_list
*
* Perhaps this should be in bitmapset.c someday.
*/
static bool
bms_equal_any(Relids relids, List *relids_list)
{
ListCell *lc;
foreach(lc, relids_list)
{
if (bms_equal(relids, (Relids) lfirst(lc)))
return true;
}
return false;
}
/*
* get_index_paths
* Given an index and a set of index clauses for it, construct IndexPaths.
*
* Plain indexpaths are sent directly to add_path, while potential
* bitmap indexpaths are added to *bitindexpaths for later processing.
*
* This is a fairly simple frontend to build_index_paths(). Its reason for
* existence is mainly to handle ScalarArrayOpExpr quals properly. If the
* index AM supports them natively, we should just include them in simple
* index paths. If not, we should exclude them while building simple index
* paths, and then make a separate attempt to include them in bitmap paths.
* Furthermore, we should consider excluding lower-order ScalarArrayOpExpr
* quals so as to create ordered paths.
*/
/*
* 根据一系列条件，生成扫描路径。此函数共被两处调用点调用。第一次用来生成普通的
* 扫描路径，第二次用来生成参数化扫描路径。
*
* 本函数调用build_index_paths三次，主要是在处理SAOP。请参考张树杰的书第261—265页。
*/
static void
get_index_paths(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index, IndexClauseSet *clauses,
List **bitindexpaths)
{
List *indexpaths;
bool skip_nonnative_saop = false;
bool skip_lower_saop = false;
ListCell *lc;
/*
* Build simple index paths using the clauses. Allow ScalarArrayOpExpr
* clauses only if the index AM supports them natively, and skip any such
* clauses for index columns after the first (so that we produce ordered
* paths if possible).
*/
indexpaths = build_index_paths(root, rel,
index, clauses,
index->predOK,
ST_ANYSCAN,
&skip_nonnative_saop,
&skip_lower_saop);
/*
* If we skipped any lower-order ScalarArrayOpExprs on an index with an AM
* that supports them, then try again including those clauses. This will
* produce paths with more selectivity but no ordering.
*/
if (skip_lower_saop)
{
indexpaths = list_concat(indexpaths,
build_index_paths(root, rel,
index, clauses,
index->predOK,
ST_ANYSCAN,
&skip_nonnative_saop,
NULL));
}
/*
* Submit all the ones that can form plain IndexScan plans to add_path. (A
* plain IndexPath can represent either a plain IndexScan or an
* IndexOnlyScan, but for our purposes here that distinction does not
* matter. However, some of the indexes might support only bitmap scans,
* and those we mustn't submit to add_path here.)
*
* Also, pick out the ones that are usable as bitmap scans. For that, we
* must discard indexes that don't support bitmap scans, and we also are
* only interested in paths that have some selectivity; we should discard
* anything that was generated solely for ordering purposes.
*/
foreach(lc, indexpaths)
{
IndexPath *ipath = (IndexPath *) lfirst(lc);
if (index->amhasgettuple)
add_path(rel, (Path *) ipath);
if (index->amhasgetbitmap &&
(ipath->path.pathkeys == NIL ||
ipath->indexselectivity < 1.0))
*bitindexpaths = lappend(*bitindexpaths, ipath);
}
/*
* If there were ScalarArrayOpExpr clauses that the index can't handle
* natively, generate bitmap scan paths relying on executor-managed
* ScalarArrayOpExpr.
*/
if (skip_nonnative_saop)
{
indexpaths = build_index_paths(root, rel,
index, clauses,
false,
ST_BITMAPSCAN,
NULL,
NULL);
*bitindexpaths = list_concat(*bitindexpaths, indexpaths);
}
}
/*
* build_index_paths
* Given an index and a set of index clauses for it, construct zero
* or more IndexPaths. It also constructs zero or more partial IndexPaths.
*
* We return a list of paths because (1) this routine checks some cases
* that should cause us to not generate any IndexPath, and (2) in some
* cases we want to consider both a forward and a backward scan, so as
* to obtain both sort orders. Note that the paths are just returned
* to the caller and not immediately fed to add_path().
*
* At top level, useful_predicate should be exactly the index's predOK flag
* (ie, true if it has a predicate that was proven from the restriction
* clauses). When working on an arm of an OR clause, useful_predicate
* should be true if the predicate required the current OR list to be proven.
* Note that this routine should never be called at all if the index has an
* unprovable predicate.
*
* scantype indicates whether we want to create plain indexscans, bitmap
* indexscans, or both. When it's ST_BITMAPSCAN, we will not consider
* index ordering while deciding if a Path is worth generating.
*
* If skip_nonnative_saop is non-NULL, we ignore ScalarArrayOpExpr clauses
* unless the index AM supports them directly, and we set *skip_nonnative_saop
* to true if we found any such clauses (caller must initialize the variable
* to false). If it's NULL, we do not ignore ScalarArrayOpExpr clauses.
*
* If skip_lower_saop is non-NULL, we ignore ScalarArrayOpExpr clauses for
* non-first index columns, and we set *skip_lower_saop to true if we found
* any such clauses (caller must initialize the variable to false). If it's
* NULL, we do not ignore non-first ScalarArrayOpExpr clauses, but they will
* result in considering the scan's output to be unordered.
*
* 'rel' is the index's heap relation
* 'index' is the index for which we want to generate paths
* 'clauses' is the collection of indexable clauses (IndexClause nodes)
* 'useful_predicate' indicates whether the index has a useful predicate
* 'scantype' indicates whether we need plain or bitmap scan support
* 'skip_nonnative_saop' indicates whether to accept SAOP if index AM doesn't
* 'skip_lower_saop' indicates whether to accept non-first-column SAOP
*/
static List *
build_index_paths(PlannerInfo *root, RelOptInfo *rel,
IndexOptInfo *index, IndexClauseSet *clauses,
bool useful_predicate,
ScanTypeControl scantype,
bool *skip_nonnative_saop,
bool *skip_lower_saop)
{
List *result = NIL;
IndexPath *ipath;
List *index_clauses;
Relids outer_relids;
double loop_count;
List *orderbyclauses;
List *orderbyclausecols;
List *index_pathkeys;
List *useful_pathkeys;
bool found_lower_saop_clause;
bool pathkeys_possibly_useful;
bool index_is_ordered;
bool index_only_scan;
int indexcol;
/*
* Check that index supports the desired scan type(s)
*/
switch (scantype)
{
case ST_INDEXSCAN:
if (!index->amhasgettuple)
return NIL;
break;
case ST_BITMAPSCAN:
if (!index->amhasgetbitmap)
return NIL;
break;
case ST_ANYSCAN:
/* either or both are OK */
break;
}
/*
* 1. Combine the per-column IndexClause lists into an overall list.
*
* In the resulting list, clauses are ordered by index key, so that the
* column numbers form a nondecreasing sequence. (This order is depended
* on by btree and possibly other places.) The list can be empty, if the
* index AM allows that.
*
* found_lower_saop_clause is set true if we accept a ScalarArrayOpExpr
* index clause for a non-first index column. This prevents us from
* assuming that the scan result is ordered. (Actually, the result is
* still ordered if there are equality constraints for all earlier
* columns, but it seems too expensive and non-modular for this code to be
* aware of that refinement.)
*
* We also build a Relids set showing which outer rels are required by the
* selected clauses. Any lateral_relids are included in that, but not
* otherwise accounted for.
*/
index_clauses = NIL;
found_lower_saop_clause = false;
outer_relids = bms_copy(rel->lateral_relids);
/* 处理SAOP */
for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)
{
ListCell *lc;
foreach(lc, clauses->indexclauses[indexcol])
{
IndexClause *iclause = (IndexClause *) lfirst(lc);
RestrictInfo *rinfo = iclause->rinfo;
/* We might need to omit ScalarArrayOpExpr clauses */
if (IsA(rinfo->clause, ScalarArrayOpExpr))
{
if (!index->amsearcharray)
{
if (skip_nonnative_saop)
{
/* Ignore because not supported by index */
*skip_nonnative_saop = true;
continue;
}
/* Caller had better intend this only for bitmap scan */
Assert(scantype == ST_BITMAPSCAN);
}
if (indexcol > 0)
{
if (skip_lower_saop)
{
/* Caller doesn't want to lose index ordering */
*skip_lower_saop = true;
continue;
}
found_lower_saop_clause = true;
}
}
/* OK to include this clause */
index_clauses = lappend(index_clauses, iclause);
outer_relids = bms_add_members(outer_relids,
rinfo->clause_relids);
}
/*
* If no clauses match the first index column, check for amoptionalkey
* restriction. We can't generate a scan over an index with
* amoptionalkey = false unless there's at least one index clause.
* (When working on columns after the first, this test cannot fail. It
* is always okay for columns after the first to not have any
* clauses.)
*/
/*
* 如果在第一个索引列上没有匹配的条件，并且这种索引必须要求在第一个索引列上
* 有匹配的条件，则返回NIL。当indexcol>0时，如果代码运行到这里，
* index_clauses一定非空，否则在index_clauses=0时，已经返回NIL了。
*/
if (index_clauses == NIL && !index->amoptionalkey)
return NIL;
}
/* We do not want the index's rel itself listed in outer_relids */
outer_relids = bms_del_member(outer_relids, rel->relid);
/* Enforce convention that outer_relids is exactly NULL if empty */
if (bms_is_empty(outer_relids))
outer_relids = NULL;
/* 估计外表可以提供多少种不同的值，即内表的路径需要循环多少次 */
/* Compute loop_count for cost estimation purposes */
loop_count = get_loop_count(root, rel->relid, outer_relids);
/*
* 2. Compute pathkeys describing index's ordering, if any, then see how
* many of them are actually useful for this query. This is not relevant
* if we are only trying to build bitmap indexscans, nor if we have to
* assume the scan is unordered.
*/
/*
* PathKey是否有用，请参考张树杰的书第266页。
*/
pathkeys_possibly_useful = (scantype != ST_BITMAPSCAN &&
!found_lower_saop_clause &&
has_useful_pathkeys(root, rel));
index_is_ordered = (index->sortopfamily != NULL);
if (index_is_ordered && pathkeys_possibly_useful)
{
index_pathkeys = build_index_pathkeys(root, index,
ForwardScanDirection);
useful_pathkeys = truncate_useless_pathkeys(root, rel,
index_pathkeys);
orderbyclauses = NIL;
orderbyclausecols = NIL;
}
else if (index->amcanorderbyop && pathkeys_possibly_useful)
{
/* amcanorderbyop表示是否支持KNN查询，btree不支持。最初只有gist索引支持 */
/* see if we can generate ordering operators for query_pathkeys */
match_pathkeys_to_index(index, root->query_pathkeys,
&orderbyclauses,
&orderbyclausecols);
if (orderbyclauses)
useful_pathkeys = root->query_pathkeys;
else
useful_pathkeys = NIL;
}
else
{
useful_pathkeys = NIL;
orderbyclauses = NIL;
orderbyclausecols = NIL;
}
/*
* 3. Check if an index-only scan is possible. If we're not building
* plain indexscans, this isn't relevant since bitmap scans don't support
* index data retrieval anyway.
*/
index_only_scan = (scantype != ST_BITMAPSCAN &&
check_index_only(rel, index));
/*
* 4. Generate an indexscan path if there are relevant restriction clauses
* in the current clauses, OR the index ordering is potentially useful for
* later merging or final output ordering, OR the index has a useful
* predicate, OR an index-only scan is possible.
*/
/* 满足这4种条件之一，才能使用索引 */
if (index_clauses != NIL || useful_pathkeys != NIL || useful_predicate ||
index_only_scan)
{
ipath = create_index_path(root, index,
index_clauses,
orderbyclauses,
orderbyclausecols,
useful_pathkeys,
index_is_ordered ?
ForwardScanDirection :
NoMovementScanDirection,
index_only_scan,
outer_relids,
loop_count,
false);
result = lappend(result, ipath);
/*
* If appropriate, consider parallel index scan. We don't allow
* parallel index scan for bitmap index scans.
*/
if (index->amcanparallel &&
rel->consider_parallel && outer_relids == NULL &&
scantype != ST_BITMAPSCAN)
{
ipath = create_index_path(root, index,
index_clauses,
orderbyclauses,
orderbyclausecols,
useful_pathkeys,
index_is_ordered ?
ForwardScanDirection :
NoMovementScanDirection,
index_only_scan,
outer_relids,
loop_count,
true);
/*
* if, after costing the path, we find that it's not worth using
* parallel workers, just free it.
*/
if (ipath->path.parallel_workers > 0)
add_partial_path(rel, (Path *) ipath);
else
pfree(ipath);
}
}
/*
* 5. If the index is ordered, a backwards scan might be interesting.
*/
if (index_is_ordered && pathkeys_possibly_useful)
{
index_pathkeys = build_index_pathkeys(root, index,
BackwardScanDirection);
useful_pathkeys = truncate_useless_pathkeys(root, rel,
index_pathkeys);
if (useful_pathkeys != NIL)
{
ipath = create_index_path(root, index,
index_clauses,
NIL,
NIL,
useful_pathkeys,
BackwardScanDirection,
index_only_scan,
outer_relids,
loop_count,
false);
result = lappend(result, ipath);
/* If appropriate, consider parallel index scan */
if (index->amcanparallel &&
rel->consider_parallel && outer_relids == NULL &&
scantype != ST_BITMAPSCAN)
{
ipath = create_index_path(root, index,
index_clauses,
NIL,
NIL,
useful_pathkeys,
BackwardScanDirection,
index_only_scan,
outer_relids,
loop_count,
true);
/*
* if, after costing the path, we find that it's not worth
* using parallel workers, just free it.
*/
if (ipath->path.parallel_workers > 0)
add_partial_path(rel, (Path *) ipath);
else
pfree(ipath);
}
}
}
return result;
}
/*
* build_paths_for_OR
* Given a list of restriction clauses from one arm of an OR clause,
* construct all matching IndexPaths for the relation.
*
* Here we must scan all indexes of the relation, since a bitmap OR tree
* can use multiple indexes.
*
* The caller actually supplies two lists of restriction clauses: some
* "current" ones and some "other" ones. Both lists can be used freely
* to match keys of the index, but an index must use at least one of the
* "current" clauses to be considered usable. The motivation for this is
* examples like
* WHERE (x = 42) AND (... OR (y = 52 AND z = 77) OR ....)
* While we are considering the y/z subclause of the OR, we can use "x = 42"
* as one of the available index conditions; but we shouldn't match the
* subclause to any index on x alone, because such a Path would already have
* been generated at the upper level. So we could use an index on x,y,z
* or an index on x,y for the OR subclause, but not an index on just x.
* When dealing with a partial index, a match of the index predicate to
* one of the "current" clauses also makes the index usable.
*
* 'rel' is the relation for which we want to generate index paths
* 'clauses' is the current list of clauses (RestrictInfo nodes)
* 'other_clauses' is the list of additional upper-level clauses
*/
/*
* 此函数被generate_bitmap_or_paths调用，建议先看generate_bitmap_or_paths，
* 再看此函数。
*
* 对查询中符合要求的OR条件中的每个子条件生成位图扫描路径，因为这个条件可能涉及
* 多个索引，因此需要迭代每一个索引。
*/
static List *
build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
List *clauses, List *other_clauses)
{
List *result = NIL;
List *all_clauses = NIL; /* not computed till needed */
ListCell *lc;
foreach(lc, rel->indexlist)
{
IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
IndexClauseSet clauseset;
List *indexpaths;
bool useful_predicate;
/* Ignore index if it doesn't support bitmap scans */
if (!index->amhasgetbitmap)
continue;
/*
* Ignore partial indexes that do not match the query. If a partial
* index is marked predOK then we know it's OK. Otherwise, we have to
* test whether the added clauses are sufficient to imply the
* predicate. If so, we can use the index in the current context.
*
* We set useful_predicate to true iff the predicate was proven using
* the current set of clauses. This is needed to prevent matching a
* predOK index to an arm of an OR, which would be a legal but
* pointlessly inefficient plan. (A better plan will be generated by
* just scanning the predOK index alone, no OR.)
*/
useful_predicate = false;
if (index->indpred != NIL)
{
if (index->predOK)
{
/* Usable, but don't set useful_predicate */
}
else
{
/* Form all_clauses if not done already */
if (all_clauses == NIL)
all_clauses = list_concat_copy(clauses, other_clauses);
if (!predicate_implied_by(index->indpred, all_clauses, false))
continue; /* can't use it at all */
if (!predicate_implied_by(index->indpred, other_clauses, false))
useful_predicate = true;
}
}
/*
* Identify the restriction clauses that can match the index.
*/
MemSet(&clauseset, 0, sizeof(clauseset));
match_clauses_to_index(root, clauses, index, &clauseset);
/*
* If no matches so far, and the index predicate isn't useful, we
* don't want it.
*/
if (!clauseset.nonempty && !useful_predicate)
continue;
/*
* Add "other" restriction clauses to the clauseset.
*/
match_clauses_to_index(root, other_clauses, index, &clauseset);
/*
* Construct paths if possible.
*/
indexpaths = build_index_paths(root, rel,
index, &clauseset,
useful_predicate,
ST_BITMAPSCAN,
NULL,
NULL);
result = list_concat(result, indexpaths);
}
return result;
}
/*
* generate_bitmap_or_paths
* Look through the list of clauses to find OR clauses, and generate
* a BitmapOrPath for each one we can handle that way. Return a list
* of the generated BitmapOrPaths.
*
* other_clauses is a list of additional clauses that can be assumed true
* for the purpose of generating indexquals, but are not to be searched for
* ORs. (See build_paths_for_OR() for motivation.)
*/
static List *
generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
List *clauses, List *other_clauses)
{
List *result = NIL;
List *all_clauses;
ListCell *lc;
/*
* We can use both the current and other clauses as context for
* build_paths_for_OR; no need to remove ORs from the lists.
*/
all_clauses = list_concat_copy(clauses, other_clauses);
foreach(lc, clauses)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
List *pathlist;
Path *bitmapqual;
ListCell *j;
/* Ignore RestrictInfos that aren't ORs */
if (!restriction_is_or_clause(rinfo))
continue;
/*
* We must be able to match at least one index to each of the arms of
* the OR, else we can't use it.
*/
pathlist = NIL;
foreach(j, ((BoolExpr *) rinfo->orclause)->args)
{
Node *orarg = (Node *) lfirst(j);
List *indlist;
/* OR arguments should be ANDs or sub-RestrictInfos */
if (is_andclause(orarg))
{
List *andargs = ((BoolExpr *) orarg)->args;
indlist = build_paths_for_OR(root, rel,
andargs,
all_clauses);
/* Recurse in case there are sub-ORs */
indlist = list_concat(indlist,
generate_bitmap_or_paths(root, rel,
andargs,
all_clauses));
}
else
{
RestrictInfo *rinfo = castNode(RestrictInfo, orarg);
List *orargs;
Assert(!restriction_is_or_clause(rinfo));
orargs = list_make1(rinfo);
indlist = build_paths_for_OR(root, rel,
orargs,
all_clauses);
}
/*
* If nothing matched this arm, we can't do anything with this OR
* clause.
*/
/*
* 既然是把OR条件拆成了多个，那么每个子条件都必须可以生成一个位图才行，任何一个
* 子条件不能生成位图，则整个OR条件不能生成位图扫描路径，结束循环，返回NIL。
*/
if (indlist == NIL)
{
pathlist = NIL;
break;
}
/*
* OK, pick the most promising AND combination, and add it to
* pathlist.
*/
bitmapqual = choose_bitmap_and(root, rel, indlist);
pathlist = lappend(pathlist, bitmapqual);
}
/*
* If we have a match for every arm, then turn them into a
* BitmapOrPath, and add to result list.
*/
if (pathlist != NIL)
{
bitmapqual = (Path *) create_bitmap_or_path(root, rel, pathlist);
result = lappend(result, bitmapqual);
}
}
return result;
}
/*
* choose_bitmap_and
* Given a nonempty list of bitmap paths, AND them into one path.
*
* This is a nontrivial decision since we can legally use any subset of the
* given path set. We want to choose a good tradeoff between selectivity
* and cost of computing the bitmap.
*
* The result is either a single one of the inputs, or a BitmapAndPath
* combining multiple inputs.
*/
/* 这个函数从一系列路径中，选出一个集合，并把它们AND起来 */
static Path *
choose_bitmap_and(PlannerInfo *root, RelOptInfo *rel, List *paths)
{
int npaths = list_length(paths);
PathClauseUsage **pathinfoarray;
PathClauseUsage *pathinfo;
List *clauselist;
List *bestpaths = NIL;
Cost bestcost = 0;
int i,
j;
ListCell *l;
Assert(npaths > 0); /* else caller error */
if (npaths == 1)
return (Path *) linitial(paths); /* easy case */
/*
* In theory we should consider every nonempty subset of the given paths.
* In practice that seems like overkill, given the crude nature of the
* estimates, not to mention the possible effects of higher-level AND and
* OR clauses. Moreover, it's completely impractical if there are a large
* number of paths, since the work would grow as O(2^N).
*
* As a heuristic, we first check for paths using exactly the same sets of
* WHERE clauses + index predicate conditions, and reject all but the
* cheapest-to-scan in any such group. This primarily gets rid of indexes
* that include the interesting columns but also irrelevant columns. (In
* situations where the DBA has gone overboard on creating variant
* indexes, this can make for a very large reduction in the number of
* paths considered further.)
*
* We then sort the surviving paths with the cheapest-to-scan first, and
* for each path, consider using that path alone as the basis for a bitmap
* scan. Then we consider bitmap AND scans formed from that path plus
* each subsequent (higher-cost) path, adding on a subsequent path if it
* results in a reduction in the estimated total scan cost. This means we
* consider about O(N^2) rather than O(2^N) path combinations, which is
* quite tolerable, especially given than N is usually reasonably small
* because of the prefiltering step. The cheapest of these is returned.
*
* We will only consider AND combinations in which no two indexes use the
* same WHERE clause. This is a bit of a kluge: it's needed because
* costsize.c and clausesel.c aren't very smart about redundant clauses.
* They will usually double-count the redundant clauses, producing a
* too-small selectivity that makes a redundant AND step look like it
* reduces the total cost. Perhaps someday that code will be smarter and
* we can remove this limitation. (But note that this also defends
* against flat-out duplicate input paths, which can happen because
* match_join_clauses_to_index will find the same OR join clauses that
* extract_restriction_or_clauses has pulled OR restriction clauses out
* of.)
*
* For the same reason, we reject AND combinations in which an index
* predicate clause duplicates another clause. Here we find it necessary
* to be even stricter: we'll reject a partial index if any of its
* predicate clauses are implied by the set of WHERE clauses and predicate
* clauses used so far. This covers cases such as a condition "x = 42"
* used with a plain index, followed by a clauseless scan of a partial
* index "WHERE x >= 40 AND x < 50". The partial index has been accepted
* only because "x = 42" was present, and so allowing it would partially
* double-count selectivity. (We could use predicate_implied_by on
* regular qual clauses too, to have a more intelligent, but much more
* expensive, check for redundancy --- but in most cases simple equality
* seems to suffice.)
*/
/*
* Extract clause usage info and detect any paths that use exactly the
* same set of clauses; keep only the cheapest-to-scan of any such groups.
* The surviving paths are put into an array for qsort'ing.
*/
pathinfoarray = (PathClauseUsage **)
palloc(npaths * sizeof(PathClauseUsage *));
clauselist = NIL;
npaths = 0;
foreach(l, paths)
{
Path *ipath = (Path *) lfirst(l);
pathinfo = classify_index_clause_usage(ipath, &clauselist);
/* If it's unclassifiable, treat it as distinct from all others */
if (pathinfo->unclassifiable)
{
pathinfoarray[npaths++] = pathinfo;
continue;
}
for (i = 0; i < npaths; i++)
{
if (!pathinfoarray[i]->unclassifiable &&
bms_equal(pathinfo->clauseids, pathinfoarray[i]->clauseids))
break;
}
if (i < npaths)
{
/* duplicate clauseids, keep the cheaper one */
Cost ncost;
Cost ocost;
Selectivity nselec;
Selectivity oselec;
cost_bitmap_tree_node(pathinfo->path, &ncost, &nselec);
cost_bitmap_tree_node(pathinfoarray[i]->path, &ocost, &oselec);
if (ncost < ocost)
pathinfoarray[i] = pathinfo;
}
else
{
/* not duplicate clauseids, add to array */
pathinfoarray[npaths++] = pathinfo;
}
}
/* If only one surviving path, we're done */
if (npaths == 1)
return pathinfoarray[0]->path;
/* Sort the surviving paths by index access cost */
qsort(pathinfoarray, npaths, sizeof(PathClauseUsage *),
path_usage_comparator);
/*
* For each surviving index, consider it as an "AND group leader", and see
* whether adding on any of the later indexes results in an AND path with
* cheaper total cost than before. Then take the cheapest AND group.
*
* Note: paths that are either clauseless or unclassifiable will have
* empty clauseids, so that they will not be rejected by the clauseids
* filter here, nor will they cause later paths to be rejected by it.
*/
for (i = 0; i < npaths; i++)
{
Cost costsofar;
List *qualsofar;
Bitmapset *clauseidsofar;
pathinfo = pathinfoarray[i];
paths = list_make1(pathinfo->path);
costsofar = bitmap_scan_cost_est(root, rel, pathinfo->path);
qualsofar = list_concat_copy(pathinfo->quals, pathinfo->preds);
clauseidsofar = bms_copy(pathinfo->clauseids);
for (j = i + 1; j < npaths; j++)
{
Cost newcost;
pathinfo = pathinfoarray[j];
/* Check for redundancy */
if (bms_overlap(pathinfo->clauseids, clauseidsofar))
continue; /* consider it redundant */
if (pathinfo->preds)
{
bool redundant = false;
/* we check each predicate clause separately */
foreach(l, pathinfo->preds)
{
Node *np = (Node *) lfirst(l);
if (predicate_implied_by(list_make1(np), qualsofar, false))
{
redundant = true;
break; /* out of inner foreach loop */
}
}
if (redundant)
continue;
}
/* tentatively add new path to paths, so we can estimate cost */
paths = lappend(paths, pathinfo->path);
newcost = bitmap_and_cost_est(root, rel, paths);
if (newcost < costsofar)
{
/* keep new path in paths, update subsidiary variables */
costsofar = newcost;
qualsofar = list_concat(qualsofar, pathinfo->quals);
qualsofar = list_concat(qualsofar, pathinfo->preds);
clauseidsofar = bms_add_members(clauseidsofar,
pathinfo->clauseids);
}
else
{
/* reject new path, remove it from paths list */
paths = list_truncate(paths, list_length(paths) - 1);
}
}
/* Keep the cheapest AND-group (or singleton) */
if (i == 0 || costsofar < bestcost)
{
bestpaths = paths;
bestcost = costsofar;
}
/* some easy cleanup (we don't try real hard though) */
list_free(qualsofar);
}
if (list_length(bestpaths) == 1)
return (Path *) linitial(bestpaths); /* no need for AND */
return (Path *) create_bitmap_and_path(root, rel, bestpaths);
}
/* qsort comparator to sort in increasing index access cost order */
static int
path_usage_comparator(const void *a, const void *b)
{
PathClauseUsage *pa = *(PathClauseUsage *const *) a;
PathClauseUsage *pb = *(PathClauseUsage *const *) b;
Cost acost;
Cost bcost;
Selectivity aselec;
Selectivity bselec;
cost_bitmap_tree_node(pa->path, &acost, &aselec);
cost_bitmap_tree_node(pb->path, &bcost, &bselec);
/*
* If costs are the same, sort by selectivity.
*/
if (acost < bcost)
return -1;
if (acost > bcost)
return 1;
if (aselec < bselec)
return -1;
if (aselec > bselec)
return 1;
return 0;
}
/*
* Estimate the cost of actually executing a bitmap scan with a single
* index path (which could be a BitmapAnd or BitmapOr node).
*/
static Cost
bitmap_scan_cost_est(PlannerInfo *root, RelOptInfo *rel, Path *ipath)
{
BitmapHeapPath bpath;
/* Set up a dummy BitmapHeapPath */
bpath.path.type = T_BitmapHeapPath;
bpath.path.pathtype = T_BitmapHeapScan;
bpath.path.parent = rel;
bpath.path.pathtarget = rel->reltarget;
bpath.path.param_info = ipath->param_info;
bpath.path.pathkeys = NIL;
bpath.bitmapqual = ipath;
/*
* Check the cost of temporary path without considering parallelism.
* Parallel bitmap heap path will be considered at later stage.
*/
bpath.path.parallel_workers = 0;
/* Now we can do cost_bitmap_heap_scan */
cost_bitmap_heap_scan(&bpath.path, root, rel,
bpath.path.param_info,
ipath,
get_loop_count(root, rel->relid,
PATH_REQ_OUTER(ipath)));
return bpath.path.total_cost;
}
/*
* Estimate the cost of actually executing a BitmapAnd scan with the given
* inputs.
*/
static Cost
bitmap_and_cost_est(PlannerInfo *root, RelOptInfo *rel, List *paths)
{
BitmapAndPath *apath;
/*
* Might as well build a real BitmapAndPath here, as the work is slightly
* too complicated to be worth repeating just to save one palloc.
*/
apath = create_bitmap_and_path(root, rel, paths);
return bitmap_scan_cost_est(root, rel, (Path *) apath);
}
/*
* classify_index_clause_usage
* Construct a PathClauseUsage struct describing the WHERE clauses and
* index predicate clauses used by the given indexscan path.
* We consider two clauses the same if they are equal().
*
* At some point we might want to migrate this info into the Path data
* structure proper, but for the moment it's only needed within
* choose_bitmap_and().
*
* *clauselist is used and expanded as needed to identify all the distinct
* clauses seen across successive calls. Caller must initialize it to NIL
* before first call of a set.
*/
static PathClauseUsage *
classify_index_clause_usage(Path *path, List **clauselist)
{
PathClauseUsage *result;
Bitmapset *clauseids;
ListCell *lc;
result = (PathClauseUsage *) palloc(sizeof(PathClauseUsage));
result->path = path;
/* Recursively find the quals and preds used by the path */
result->quals = NIL;
result->preds = NIL;
find_indexpath_quals(path, &result->quals, &result->preds);
/*
* Some machine-generated queries have outlandish numbers of qual clauses.
* To avoid getting into O(N^2) behavior even in this preliminary
* classification step, we want to limit the number of entries we can
* accumulate in *clauselist. Treat any path with more than 100 quals +
* preds as unclassifiable, which will cause calling code to consider it
* distinct from all other paths.
*/
if (list_length(result->quals) + list_length(result->preds) > 100)
{
result->clauseids = NULL;
result->unclassifiable = true;
return result;
}
/* Build up a bitmapset representing the quals and preds */
clauseids = NULL;
foreach(lc, result->quals)
{
Node *node = (Node *) lfirst(lc);
clauseids = bms_add_member(clauseids,
find_list_position(node, clauselist));
}
foreach(lc, result->preds)
{
Node *node = (Node *) lfirst(lc);
clauseids = bms_add_member(clauseids,
find_list_position(node, clauselist));
}
result->clauseids = clauseids;
result->unclassifiable = false;
return result;
}
/*
* find_indexpath_quals
*
* Given the Path structure for a plain or bitmap indexscan, extract lists
* of all the index clauses and index predicate conditions used in the Path.
* These are appended to the initial contents of *quals and *preds (hence
* caller should initialize those to NIL).
*
* Note we are not trying to produce an accurate representation of the AND/OR
* semantics of the Path, but just find out all the base conditions used.
*
* The result lists contain pointers to the expressions used in the Path,
* but all the list cells are freshly built, so it's safe to destructively
* modify the lists (eg, by concat'ing with other lists).
*/
static void
find_indexpath_quals(Path *bitmapqual, List **quals, List **preds)
{
if (IsA(bitmapqual, BitmapAndPath))
{
BitmapAndPath *apath = (BitmapAndPath *) bitmapqual;
ListCell *l;
foreach(l, apath->bitmapquals)
{
find_indexpath_quals((Path *) lfirst(l), quals, preds);
}
}
else if (IsA(bitmapqual, BitmapOrPath))
{
BitmapOrPath *opath = (BitmapOrPath *) bitmapqual;
ListCell *l;
foreach(l, opath->bitmapquals)
{
find_indexpath_quals((Path *) lfirst(l), quals, preds);
}
}
else if (IsA(bitmapqual, IndexPath))
{
IndexPath *ipath = (IndexPath *) bitmapqual;
ListCell *l;
foreach(l, ipath->indexclauses)
{
IndexClause *iclause = (IndexClause *) lfirst(l);
*quals = lappend(*quals, iclause->rinfo->clause);
}
*preds = list_concat(*preds, ipath->indexinfo->indpred);
}
else
elog(ERROR, "unrecognized node type: %d", nodeTag(bitmapqual));
}
/*
* find_list_position
* Return the given node's position (counting from 0) in the given
* list of nodes. If it's not equal() to any existing list member,
* add it at the end, and return that position.
*/
static int
find_list_position(Node *node, List **nodelist)
{
int i;
ListCell *lc;
i = 0;
foreach(lc, *nodelist)
{
Node *oldnode = (Node *) lfirst(lc);
if (equal(node, oldnode))
return i;
i++;
}
*nodelist = lappend(*nodelist, node);
return i;
}
/*
* check_index_only
* Determine whether an index-only scan is possible for this index.
*/
static bool
check_index_only(RelOptInfo *rel, IndexOptInfo *index)
{
bool result;
Bitmapset *attrs_used = NULL;
Bitmapset *index_canreturn_attrs = NULL;
Bitmapset *index_cannotreturn_attrs = NULL;
ListCell *lc;
int i;
/* Index-only scans must be enabled */
if (!enable_indexonlyscan)
return false;
/*
* Check that all needed attributes of the relation are available from the
* index.
*/
/*
* First, identify all the attributes needed for joins or final output.
* Note: we must look at rel's targetlist, not the attr_needed data,
* because attr_needed isn't computed for inheritance child rels.
*/
pull_varattnos((Node *) rel->reltarget->exprs, rel->relid, &attrs_used);
/*
* Add all the attributes used by restriction clauses; but consider only
* those clauses not implied by the index predicate, since ones that are
* so implied don't need to be checked explicitly in the plan.
*
* Note: attributes used only in index quals would not be needed at
* runtime either, if we are certain that the index is not lossy. However
* it'd be complicated to account for that accurately, and it doesn't
* matter in most cases, since we'd conclude that such attributes are
* available from the index anyway.
*/
foreach(lc, index->indrestrictinfo)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
pull_varattnos((Node *) rinfo->clause, rel->relid, &attrs_used);
}
/*
* Construct a bitmapset of columns that the index can return back in an
* index-only scan. If there are multiple index columns containing the
* same attribute, all of them must be capable of returning the value,
* since we might recheck operators on any of them. (Potentially we could
* be smarter about that, but it's such a weird situation that it doesn't
* seem worth spending a lot of sweat on.)
*/
for (i = 0; i < index->ncolumns; i++)
{
int attno = index->indexkeys[i];
/*
* For the moment, we just ignore index expressions. It might be nice
* to do something with them, later.
*/
if (attno == 0)
continue;
if (index->canreturn[i])
index_canreturn_attrs =
bms_add_member(index_canreturn_attrs,
attno - FirstLowInvalidHeapAttributeNumber);
else
index_cannotreturn_attrs =
bms_add_member(index_cannotreturn_attrs,
attno - FirstLowInvalidHeapAttributeNumber);
}
index_canreturn_attrs = bms_del_members(index_canreturn_attrs,
index_cannotreturn_attrs);
/* Do we have all the necessary attributes? */
result = bms_is_subset(attrs_used, index_canreturn_attrs);
bms_free(attrs_used);
bms_free(index_canreturn_attrs);
bms_free(index_cannotreturn_attrs);
return result;
}
/*
* get_loop_count
* Choose the loop count estimate to use for costing a parameterized path
* with the given set of outer relids.
*
* Since we produce parameterized paths before we've begun to generate join
* relations, it's impossible to predict exactly how many times a parameterized
* path will be iterated; we don't know the size of the relation that will be
* on the outside of the nestloop. However, we should try to account for
* multiple iterations somehow in costing the path. The heuristic embodied
* here is to use the rowcount of the smallest other base relation needed in
* the join clauses used by the path. (We could alternatively consider the
* largest one, but that seems too optimistic.) This is of course the right
* answer for single-other-relation cases, and it seems like a reasonable
* zero-order approximation for multiway-join cases.
*
* In addition, we check to see if the other side of each join clause is on
* the inside of some semijoin that the current relation is on the outside of.
* If so, the only way that a parameterized path could be used is if the
* semijoin RHS has been unique-ified, so we should use the number of unique
* RHS rows rather than using the relation's raw rowcount.
*
* Note: for this to work, allpaths.c must establish all baserel size
* estimates before it begins to compute paths, or at least before it
* calls create_index_paths().
*/
static double
get_loop_count(PlannerInfo *root, Index cur_relid, Relids outer_relids)
{
double result;
int outer_relid;
/* For a non-parameterized path, just return 1.0 quickly */
if (outer_relids == NULL)
return 1.0;
result = 0.0;
outer_relid = -1;
while ((outer_relid = bms_next_member(outer_relids, outer_relid)) >= 0)
{
RelOptInfo *outer_rel;
double rowcount;
/* Paranoia: ignore bogus relid indexes */
if (outer_relid >= root->simple_rel_array_size)
continue;
outer_rel = root->simple_rel_array[outer_relid];
if (outer_rel == NULL)
continue;
Assert(outer_rel->relid == outer_relid); /* sanity check on array */
/* Other relation could be proven empty, if so ignore */
if (IS_DUMMY_REL(outer_rel))
continue;
/* Otherwise, rel's rows estimate should be valid by now */
Assert(outer_rel->rows > 0);
/* Check to see if rel is on the inside of any semijoins */
rowcount = adjust_rowcount_for_semijoins(root,
cur_relid,
outer_relid,
outer_rel->rows);
/* Remember smallest row count estimate among the outer rels */
if (result == 0.0 || result > rowcount)
result = rowcount;
}
/* Return 1.0 if we found no valid relations (shouldn't happen) */
return (result > 0.0) ? result : 1.0;
}
/*
* Check to see if outer_relid is on the inside of any semijoin that cur_relid
* is on the outside of. If so, replace rowcount with the estimated number of
* unique rows from the semijoin RHS (assuming that's smaller, which it might
* not be). The estimate is crude but it's the best we can do at this stage
* of the proceedings.
*/
static double
adjust_rowcount_for_semijoins(PlannerInfo *root,
Index cur_relid,
Index outer_relid,
double rowcount)
{
ListCell *lc;
foreach(lc, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
if (sjinfo->jointype == JOIN_SEMI &&
bms_is_member(cur_relid, sjinfo->syn_lefthand) &&
bms_is_member(outer_relid, sjinfo->syn_righthand))
{
/* Estimate number of unique-ified rows */
double nraw;
double nunique;
nraw = approximate_joinrel_size(root, sjinfo->syn_righthand);
nunique = estimate_num_groups(root,
sjinfo->semi_rhs_exprs,
nraw,
NULL);
if (rowcount > nunique)
rowcount = nunique;
}
}
return rowcount;
}
/*
* Make an approximate estimate of the size of a joinrel.
*
* We don't have enough info at this point to get a good estimate, so we
* just multiply the base relation sizes together. Fortunately, this is
* the right answer anyway for the most common case with a single relation
* on the RHS of a semijoin. Also, estimate_num_groups() has only a weak
* dependency on its input_rows argument (it basically uses it as a clamp).
* So we might be able to get a fairly decent end result even with a severe
* overestimate of the RHS's raw size.
*/
static double
approximate_joinrel_size(PlannerInfo *root, Relids relids)
{
double rowcount = 1.0;
int relid;
relid = -1;
while ((relid = bms_next_member(relids, relid)) >= 0)
{
RelOptInfo *rel;
/* Paranoia: ignore bogus relid indexes */
if (relid >= root->simple_rel_array_size)
continue;
rel = root->simple_rel_array[relid];
if (rel == NULL)
continue;
Assert(rel->relid == relid); /* sanity check on array */
/* Relation could be proven empty, if so ignore */
if (IS_DUMMY_REL(rel))
continue;
/* Otherwise, rel's rows estimate should be valid by now */
Assert(rel->rows > 0);
/* Accumulate product */
rowcount *= rel->rows;
}
return rowcount;
}
/****************************************************************************
* ---- ROUTINES TO CHECK QUERY CLAUSES ----
****************************************************************************/
/*
* match_restriction_clauses_to_index
* Identify restriction clauses for the rel that match the index.
* Matching clauses are added to *clauseset.
*/
static void
match_restriction_clauses_to_index(PlannerInfo *root,
IndexOptInfo *index,
IndexClauseSet *clauseset)
{
/* We can ignore clauses that are implied by the index predicate */
match_clauses_to_index(root, index->indrestrictinfo, index, clauseset);
}
/*
* match_join_clauses_to_index
* Identify join clauses for the rel that match the index.
* Matching clauses are added to *clauseset.
* Also, add any potentially usable join OR clauses to *joinorclauses.
*/
static void
match_join_clauses_to_index(PlannerInfo *root,
RelOptInfo *rel, IndexOptInfo *index,
IndexClauseSet *clauseset,
List **joinorclauses)
{
ListCell *lc;
/* Scan the rel's join clauses */
foreach(lc, rel->joininfo)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
/* Check if clause can be moved to this rel */
if (!join_clause_is_movable_to(rinfo, rel))
continue;
/* Potentially usable, so see if it matches the index or is an OR */
if (restriction_is_or_clause(rinfo))
*joinorclauses = lappend(*joinorclauses, rinfo);
else
match_clause_to_index(root, rinfo, index, clauseset);
}
}
/*
* match_eclass_clauses_to_index
* Identify EquivalenceClass join clauses for the rel that match the index.
* Matching clauses are added to *clauseset.
*/
static void
match_eclass_clauses_to_index(PlannerInfo *root, IndexOptInfo *index,
IndexClauseSet *clauseset)
{
int indexcol;
/* No work if rel is not in any such ECs */
if (!index->rel->has_eclass_joins)
return;
for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)
{
ec_member_matches_arg arg;
List *clauses;
/* Generate clauses, skipping any that join to lateral_referencers */
arg.index = index;
arg.indexcol = indexcol;
clauses = generate_implied_equalities_for_column(root,
index->rel,
ec_member_matches_indexcol,
(void *) &arg,
index->rel->lateral_referencers);
/*
* We have to check whether the results actually do match the index,
* since for non-btree indexes the EC's equality operators might not
* be in the index opclass (cf ec_member_matches_indexcol).
*/
match_clauses_to_index(root, clauses, index, clauseset);
}
}
/*
* match_clauses_to_index
* Perform match_clause_to_index() for each clause in a list.
* Matching clauses are added to *clauseset.
*/
static void
match_clauses_to_index(PlannerInfo *root,
List *clauses,
IndexOptInfo *index,
IndexClauseSet *clauseset)
{
ListCell *lc;
foreach(lc, clauses)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
match_clause_to_index(root, rinfo, index, clauseset);
}
}
/*
* match_clause_to_index
* Test whether a qual clause can be used with an index.
*
* If the clause is usable, add an IndexClause entry for it to the appropriate
* list in *clauseset. (*clauseset must be initialized to zeroes before first
* call.)
*
* Note: in some circumstances we may find the same RestrictInfos coming from
* multiple places. Defend against redundant outputs by refusing to add a
* clause twice (pointer equality should be a good enough check for this).
*
* Note: it's possible that a badly-defined index could have multiple matching
* columns. We always select the first match if so; this avoids scenarios
* wherein we get an inflated idea of the index's selectivity by using the
* same clause multiple times with different index columns.
*/
static void
match_clause_to_index(PlannerInfo *root,
RestrictInfo *rinfo,
IndexOptInfo *index,
IndexClauseSet *clauseset)
{
int indexcol;
/*
* Never match pseudoconstants to indexes. (Normally a match could not
* happen anyway, since a pseudoconstant clause couldn't contain a Var,
* but what if someone builds an expression index on a constant? It's not
* totally unreasonable to do so with a partial index, either.)
*/
if (rinfo->pseudoconstant)
return;
/*
* If clause can't be used as an indexqual because it must wait till after
* some lower-security-level restriction clause, reject it.
*/
if (!restriction_is_securely_promotable(rinfo, index->rel))
return;
/* OK, check each index key column for a match */
for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)
{
IndexClause *iclause;
ListCell *lc;
/* Ignore duplicates */
foreach(lc, clauseset->indexclauses[indexcol])
{
IndexClause *iclause = (IndexClause *) lfirst(lc);
if (iclause->rinfo == rinfo)
return;
}
/* OK, try to match the clause to the index column */
iclause = match_clause_to_indexcol(root,
rinfo,
indexcol,
index);
if (iclause)
{
/* Success, so record it */
clauseset->indexclauses[indexcol] =
lappend(clauseset->indexclauses[indexcol], iclause);
clauseset->nonempty = true;
return;
}
}
}
/*
* match_clause_to_indexcol()
* Determine whether a restriction clause matches a column of an index,
* and if so, build an IndexClause node describing the details.
*
* To match an index normally, an operator clause:
*
* (1) must be in the form (indexkey op const) or (const op indexkey);
* and
* (2) must contain an operator which is in the index's operator family
* for this column; and
* (3) must match the collation of the index, if collation is relevant.
*
* Our definition of "const" is exceedingly liberal: we allow anything that
* doesn't involve a volatile function or a Var of the index's relation.
* In particular, Vars belonging to other relations of the query are
* accepted here, since a clause of that form can be used in a
* parameterized indexscan. It's the responsibility of higher code levels
* to manage restriction and join clauses appropriately.
*
* Note: we do need to check for Vars of the index's relation on the
* "const" side of the clause, since clauses like (a.f1 OP (b.f2 OP a.f3))
* are not processable by a parameterized indexscan on a.f1, whereas
* something like (a.f1 OP (b.f2 OP c.f3)) is.
*
* Presently, the executor can only deal with indexquals that have the
* indexkey on the left, so we can only use clauses that have the indexkey
* on the right if we can commute the clause to put the key on the left.
* We handle that by generating an IndexClause with the correctly-commuted
* opclause as a derived indexqual.
*
* If the index has a collation, the clause must have the same collation.
* For collation-less indexes, we assume it doesn't matter; this is
* necessary for cases like "hstore ? text", wherein hstore's operators
* don't care about collation but the clause will get marked with a
* collation anyway because of the text argument. (This logic is
* embodied in the macro IndexCollMatchesExprColl.)
*
* It is also possible to match RowCompareExpr clauses to indexes (but
* currently, only btree indexes handle this).
*
* It is also possible to match ScalarArrayOpExpr clauses to indexes, when
* the clause is of the form "indexkey op ANY (arrayconst)".
*
* For boolean indexes, it is also possible to match the clause directly
* to the indexkey; or perhaps the clause is (NOT indexkey).
*
* And, last but not least, some operators and functions can be processed
* to derive (typically lossy) indexquals from a clause that isn't in
* itself indexable. If we see that any operand of an OpExpr or FuncExpr
* matches the index key, and the function has a planner support function
* attached to it, we'll invoke the support function to see if such an
* indexqual can be built.
*
* 'rinfo' is the clause to be tested (as a RestrictInfo node).
* 'indexcol' is a column number of 'index' (counting from 0).
* 'index' is the index of interest.
*
* Returns an IndexClause if the clause can be used with this index key,
* or NULL if not.
*
* NOTE: returns NULL if clause is an OR or AND clause; it is the
* responsibility of higher-level routines to cope with those.
*/
static IndexClause *
match_clause_to_indexcol(PlannerInfo *root,
RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index)
{
IndexClause *iclause;
Expr *clause = rinfo->clause;
Oid opfamily;
Assert(indexcol < index->nkeycolumns);
/*
* Historically this code has coped with NULL clauses. That's probably
* not possible anymore, but we might as well continue to cope.
*/
if (clause == NULL)
return NULL;
/* First check for boolean-index cases. */
opfamily = index->opfamily[indexcol];
if (IsBooleanOpfamily(opfamily))
{
iclause = match_boolean_index_clause(rinfo, indexcol, index);
if (iclause)
return iclause;
}
/*
* Clause must be an opclause, funcclause, ScalarArrayOpExpr, or
* RowCompareExpr. Or, if the index supports it, we can handle IS
* NULL/NOT NULL clauses.
*/
if (IsA(clause, OpExpr))
{
return match_opclause_to_indexcol(root, rinfo, indexcol, index);
}
else if (IsA(clause, FuncExpr))
{
return match_funcclause_to_indexcol(root, rinfo, indexcol, index);
}
else if (IsA(clause, ScalarArrayOpExpr))
{
return match_saopclause_to_indexcol(rinfo, indexcol, index);
}
else if (IsA(clause, RowCompareExpr))
{
return match_rowcompare_to_indexcol(rinfo, indexcol, index);
}
else if (index->amsearchnulls && IsA(clause, NullTest))
{
NullTest *nt = (NullTest *) clause;
if (!nt->argisrow &&
match_index_to_operand((Node *) nt->arg, indexcol, index))
{
iclause = makeNode(IndexClause);
iclause->rinfo = rinfo;
iclause->indexquals = list_make1(rinfo);
iclause->lossy = false;
iclause->indexcol = indexcol;
iclause->indexcols = NIL;
return iclause;
}
}
return NULL;
}
/*
* match_boolean_index_clause
* Recognize restriction clauses that can be matched to a boolean index.
*
* The idea here is that, for an index on a boolean column that supports the
* BooleanEqualOperator, we can transform a plain reference to the indexkey
* into "indexkey = true", or "NOT indexkey" into "indexkey = false", etc,
* so as to make the expression indexable using the index's "=" operator.
* Since Postgres 8.1, we must do this because constant simplification does
* the reverse transformation; without this code there'd be no way to use
* such an index at all.
*
* This should be called only when IsBooleanOpfamily() recognizes the
* index's operator family. We check to see if the clause matches the
* index's key, and if so, build a suitable IndexClause.
*/
static IndexClause *
match_boolean_index_clause(RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index)
{
Node *clause = (Node *) rinfo->clause;
Expr *op = NULL;
/* Direct match? */
if (match_index_to_operand(clause, indexcol, index))
{
/* convert to indexkey = TRUE */
op = make_opclause(BooleanEqualOperator, BOOLOID, false,
(Expr *) clause,
(Expr *) makeBoolConst(true, false),
InvalidOid, InvalidOid);
}
/* NOT clause? */
else if (is_notclause(clause))
{
Node *arg = (Node *) get_notclausearg((Expr *) clause);
if (match_index_to_operand(arg, indexcol, index))
{
/* convert to indexkey = FALSE */
op = make_opclause(BooleanEqualOperator, BOOLOID, false,
(Expr *) arg,
(Expr *) makeBoolConst(false, false),
InvalidOid, InvalidOid);
}
}
/*
* Since we only consider clauses at top level of WHERE, we can convert
* indexkey IS TRUE and indexkey IS FALSE to index searches as well. The
* different meaning for NULL isn't important.
*/
else if (clause && IsA(clause, BooleanTest))
{
BooleanTest *btest = (BooleanTest *) clause;
Node *arg = (Node *) btest->arg;
if (btest->booltesttype == IS_TRUE &&
match_index_to_operand(arg, indexcol, index))
{
/* convert to indexkey = TRUE */
op = make_opclause(BooleanEqualOperator, BOOLOID, false,
(Expr *) arg,
(Expr *) makeBoolConst(true, false),
InvalidOid, InvalidOid);
}
else if (btest->booltesttype == IS_FALSE &&
match_index_to_operand(arg, indexcol, index))
{
/* convert to indexkey = FALSE */
op = make_opclause(BooleanEqualOperator, BOOLOID, false,
(Expr *) arg,
(Expr *) makeBoolConst(false, false),
InvalidOid, InvalidOid);
}
}
/*
* If we successfully made an operator clause from the given qual, we must
* wrap it in an IndexClause. It's not lossy.
*/
if (op)
{
IndexClause *iclause = makeNode(IndexClause);
iclause->rinfo = rinfo;
iclause->indexquals = list_make1(make_simple_restrictinfo(op));
iclause->lossy = false;
iclause->indexcol = indexcol;
iclause->indexcols = NIL;
return iclause;
}
return NULL;
}
/*
* match_opclause_to_indexcol()
* Handles the OpExpr case for match_clause_to_indexcol(),
* which see for comments.
*/
static IndexClause *
match_opclause_to_indexcol(PlannerInfo *root,
RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index)
{
IndexClause *iclause;
OpExpr *clause = (OpExpr *) rinfo->clause;
Node *leftop,
*rightop;
Oid expr_op;
Oid expr_coll;
Index index_relid;
Oid opfamily;
Oid idxcollation;
/*
* Only binary operators need apply. (In theory, a planner support
* function could do something with a unary operator, but it seems
* unlikely to be worth the cycles to check.)
*/
if (list_length(clause->args) != 2)
return NULL;
leftop = (Node *) linitial(clause->args);
rightop = (Node *) lsecond(clause->args);
expr_op = clause->opno;
expr_coll = clause->inputcollid;
index_relid = index->rel->relid;
opfamily = index->opfamily[indexcol];
idxcollation = index->indexcollations[indexcol];
/*
* Check for clauses of the form: (indexkey operator constant) or
* (constant operator indexkey). See match_clause_to_indexcol's notes
* about const-ness.
*
* Note that we don't ask the support function about clauses that don't
* have one of these forms. Again, in principle it might be possible to
* do something, but it seems unlikely to be worth the cycles to check.
*/
if (match_index_to_operand(leftop, indexcol, index) &&
!bms_is_member(index_relid, rinfo->right_relids) &&
!contain_volatile_functions(rightop))
{
if (IndexCollMatchesExprColl(idxcollation, expr_coll) &&
op_in_opfamily(expr_op, opfamily))
{
iclause = makeNode(IndexClause);
iclause->rinfo = rinfo;
iclause->indexquals = list_make1(rinfo);
iclause->lossy = false;
iclause->indexcol = indexcol;
iclause->indexcols = NIL;
return iclause;
}
/*
* If we didn't find a member of the index's opfamily, try the support
* function for the operator's underlying function.
*/
set_opfuncid(clause); /* make sure we have opfuncid */
return get_index_clause_from_support(root,
rinfo,
clause->opfuncid,
0, /* indexarg on left */
indexcol,
index);
}
if (match_index_to_operand(rightop, indexcol, index) &&
!bms_is_member(index_relid, rinfo->left_relids) &&
!contain_volatile_functions(leftop))
{
if (IndexCollMatchesExprColl(idxcollation, expr_coll))
{
Oid comm_op = get_commutator(expr_op);
if (OidIsValid(comm_op) &&
op_in_opfamily(comm_op, opfamily))
{
RestrictInfo *commrinfo;
/* Build a commuted OpExpr and RestrictInfo */
commrinfo = commute_restrictinfo(rinfo, comm_op);
/* Make an IndexClause showing that as a derived qual */
iclause = makeNode(IndexClause);
iclause->rinfo = rinfo;
iclause->indexquals = list_make1(commrinfo);
iclause->lossy = false;
iclause->indexcol = indexcol;
iclause->indexcols = NIL;
return iclause;
}
}
/*
* If we didn't find a member of the index's opfamily, try the support
* function for the operator's underlying function.
*/
set_opfuncid(clause); /* make sure we have opfuncid */
return get_index_clause_from_support(root,
rinfo,
clause->opfuncid,
1, /* indexarg on right */
indexcol,
index);
}
return NULL;
}
/*
* match_funcclause_to_indexcol()
* Handles the FuncExpr case for match_clause_to_indexcol(),
* which see for comments.
*/
static IndexClause *
match_funcclause_to_indexcol(PlannerInfo *root,
RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index)
{
FuncExpr *clause = (FuncExpr *) rinfo->clause;
int indexarg;
ListCell *lc;
/*
* We have no built-in intelligence about function clauses, but if there's
* a planner support function, it might be able to do something. But, to
* cut down on wasted planning cycles, only call the support function if
* at least one argument matches the target index column.
*
* Note that we don't insist on the other arguments being pseudoconstants;
* the support function has to check that. This is to allow cases where
* only some of the other arguments need to be included in the indexqual.
*/
indexarg = 0;
foreach(lc, clause->args)
{
Node *op = (Node *) lfirst(lc);
if (match_index_to_operand(op, indexcol, index))
{
return get_index_clause_from_support(root,
rinfo,
clause->funcid,
indexarg,
indexcol,
index);
}
indexarg++;
}
return NULL;
}
/*
* get_index_clause_from_support()
* If the function has a planner support function, try to construct
* an IndexClause using indexquals created by the support function.
*/
static IndexClause *
get_index_clause_from_support(PlannerInfo *root,
RestrictInfo *rinfo,
Oid funcid,
int indexarg,
int indexcol,
IndexOptInfo *index)
{
Oid prosupport = get_func_support(funcid);
SupportRequestIndexCondition req;
List *sresult;
if (!OidIsValid(prosupport))
return NULL;
req.type = T_SupportRequestIndexCondition;
req.root = root;
req.funcid = funcid;
req.node = (Node *) rinfo->clause;
req.indexarg = indexarg;
req.index = index;
req.indexcol = indexcol;
req.opfamily = index->opfamily[indexcol];
req.indexcollation = index->indexcollations[indexcol];
req.lossy = true; /* default assumption */
sresult = (List *)
DatumGetPointer(OidFunctionCall1(prosupport,
PointerGetDatum(&req)));
if (sresult != NIL)
{
IndexClause *iclause = makeNode(IndexClause);
List *indexquals = NIL;
ListCell *lc;
/*
* The support function API says it should just give back bare
* clauses, so here we must wrap each one in a RestrictInfo.
*/
foreach(lc, sresult)
{
Expr *clause = (Expr *) lfirst(lc);
indexquals = lappend(indexquals, make_simple_restrictinfo(clause));
}
iclause->rinfo = rinfo;
iclause->indexquals = indexquals;
iclause->lossy = req.lossy;
iclause->indexcol = indexcol;
iclause->indexcols = NIL;
return iclause;
}
return NULL;
}
/*
* match_saopclause_to_indexcol()
* Handles the ScalarArrayOpExpr case for match_clause_to_indexcol(),
* which see for comments.
*/
static IndexClause *
match_saopclause_to_indexcol(RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index)
{
ScalarArrayOpExpr *saop = (ScalarArrayOpExpr *) rinfo->clause;
Node *leftop,
*rightop;
Relids right_relids;
Oid expr_op;
Oid expr_coll;
Index index_relid;
Oid opfamily;
Oid idxcollation;
/* We only accept ANY clauses, not ALL */
if (!saop->useOr)
return NULL;
leftop = (Node *) linitial(saop->args);
rightop = (Node *) lsecond(saop->args);
right_relids = pull_varnos(rightop);
expr_op = saop->opno;
expr_coll = saop->inputcollid;
index_relid = index->rel->relid;
opfamily = index->opfamily[indexcol];
idxcollation = index->indexcollations[indexcol];
/*
* We must have indexkey on the left and a pseudo-constant array argument.
*/
if (match_index_to_operand(leftop, indexcol, index) &&
!bms_is_member(index_relid, right_relids) &&
!contain_volatile_functions(rightop))
{
if (IndexCollMatchesExprColl(idxcollation, expr_coll) &&
op_in_opfamily(expr_op, opfamily))
{
IndexClause *iclause = makeNode(IndexClause);
iclause->rinfo = rinfo;
iclause->indexquals = list_make1(rinfo);
iclause->lossy = false;
iclause->indexcol = indexcol;
iclause->indexcols = NIL;
return iclause;
}
/*
* We do not currently ask support functions about ScalarArrayOpExprs,
* though in principle we could.
*/
}
return NULL;
}
/*
* match_rowcompare_to_indexcol()
* Handles the RowCompareExpr case for match_clause_to_indexcol(),
* which see for comments.
*
* In this routine we check whether the first column of the row comparison
* matches the target index column. This is sufficient to guarantee that some
* index condition can be constructed from the RowCompareExpr --- the rest
* is handled by expand_indexqual_rowcompare().
*/
static IndexClause *
match_rowcompare_to_indexcol(RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index)
{
RowCompareExpr *clause = (RowCompareExpr *) rinfo->clause;
Index index_relid;
Oid opfamily;
Oid idxcollation;
Node *leftop,
*rightop;
bool var_on_left;
Oid expr_op;
Oid expr_coll;
/* Forget it if we're not dealing with a btree index */
if (index->relam != BTREE_AM_OID)
return NULL;
index_relid = index->rel->relid;
opfamily = index->opfamily[indexcol];
idxcollation = index->indexcollations[indexcol];
/*
* We could do the matching on the basis of insisting that the opfamily
* shown in the RowCompareExpr be the same as the index column's opfamily,
* but that could fail in the presence of reverse-sort opfamilies: it'd be
* a matter of chance whether RowCompareExpr had picked the forward or
* reverse-sort family. So look only at the operator, and match if it is
* a member of the index's opfamily (after commutation, if the indexkey is
* on the right). We'll worry later about whether any additional
* operators are matchable to the index.
*/
leftop = (Node *) linitial(clause->largs);
rightop = (Node *) linitial(clause->rargs);
expr_op = linitial_oid(clause->opnos);
expr_coll = linitial_oid(clause->inputcollids);
/* Collations must match, if relevant */
if (!IndexCollMatchesExprColl(idxcollation, expr_coll))
return NULL;
/*
* These syntactic tests are the same as in match_opclause_to_indexcol()
*/
if (match_index_to_operand(leftop, indexcol, index) &&
!bms_is_member(index_relid, pull_varnos(rightop)) &&
!contain_volatile_functions(rightop))
{
/* OK, indexkey is on left */
var_on_left = true;
}
else if (match_index_to_operand(rightop, indexcol, index) &&
!bms_is_member(index_relid, pull_varnos(leftop)) &&
!contain_volatile_functions(leftop))
{
/* indexkey is on right, so commute the operator */
expr_op = get_commutator(expr_op);
if (expr_op == InvalidOid)
return NULL;
var_on_left = false;
}
else
return NULL;
/* We're good if the operator is the right type of opfamily member */
switch (get_op_opfamily_strategy(expr_op, opfamily))
{
case BTLessStrategyNumber:
case BTLessEqualStrategyNumber:
case BTGreaterEqualStrategyNumber:
case BTGreaterStrategyNumber:
return expand_indexqual_rowcompare(rinfo,
indexcol,
index,
expr_op,
var_on_left);
}
return NULL;
}
/*
* expand_indexqual_rowcompare --- expand a single indexqual condition
* that is a RowCompareExpr
*
* It's already known that the first column of the row comparison matches
* the specified column of the index. We can use additional columns of the
* row comparison as index qualifications, so long as they match the index
* in the "same direction", ie, the indexkeys are all on the same side of the
* clause and the operators are all the same-type members of the opfamilies.
*
* If all the columns of the RowCompareExpr match in this way, we just use it
* as-is, except for possibly commuting it to put the indexkeys on the left.
*
* Otherwise, we build a shortened RowCompareExpr (if more than one
* column matches) or a simple OpExpr (if the first-column match is all
* there is). In these cases the modified clause is always "<=" or ">="
* even when the original was "<" or ">" --- this is necessary to match all
* the rows that could match the original. (We are building a lossy version
* of the row comparison when we do this, so we set lossy = true.)
*
* Note: this is really just the last half of match_rowcompare_to_indexcol,
* but we split it out for comprehensibility.
*/
static IndexClause *
expand_indexqual_rowcompare(RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index,
Oid expr_op,
bool var_on_left)
{
IndexClause *iclause = makeNode(IndexClause);
RowCompareExpr *clause = (RowCompareExpr *) rinfo->clause;
int op_strategy;
Oid op_lefttype;
Oid op_righttype;
int matching_cols;
List *expr_ops;
List *opfamilies;
List *lefttypes;
List *righttypes;
List *new_ops;
List *var_args;
List *non_var_args;
iclause->rinfo = rinfo;
iclause->indexcol = indexcol;
if (var_on_left)
{
var_args = clause->largs;
non_var_args = clause->rargs;
}
else
{
var_args = clause->rargs;
non_var_args = clause->largs;
}
get_op_opfamily_properties(expr_op, index->opfamily[indexcol], false,
&op_strategy,
&op_lefttype,
&op_righttype);
/* Initialize returned list of which index columns are used */
iclause->indexcols = list_make1_int(indexcol);
/* Build lists of ops, opfamilies and operator datatypes in case needed */
expr_ops = list_make1_oid(expr_op);
opfamilies = list_make1_oid(index->opfamily[indexcol]);
lefttypes = list_make1_oid(op_lefttype);
righttypes = list_make1_oid(op_righttype);
/*
* See how many of the remaining columns match some index column in the
* same way. As in match_clause_to_indexcol(), the "other" side of any
* potential index condition is OK as long as it doesn't use Vars from the
* indexed relation.
*/
matching_cols = 1;
while (matching_cols < list_length(var_args))
{
Node *varop = (Node *) list_nth(var_args, matching_cols);
Node *constop = (Node *) list_nth(non_var_args, matching_cols);
int i;
expr_op = list_nth_oid(clause->opnos, matching_cols);
if (!var_on_left)
{
/* indexkey is on right, so commute the operator */
expr_op = get_commutator(expr_op);
if (expr_op == InvalidOid)
break; /* operator is not usable */
}
if (bms_is_member(index->rel->relid, pull_varnos(constop)))
break; /* no good, Var on wrong side */
if (contain_volatile_functions(constop))
break; /* no good, volatile comparison value */
/*
* The Var side can match any key column of the index.
*/
for (i = 0; i < index->nkeycolumns; i++)
{
if (match_index_to_operand(varop, i, index) &&
get_op_opfamily_strategy(expr_op,
index->opfamily[i]) == op_strategy &&
IndexCollMatchesExprColl(index->indexcollations[i],
list_nth_oid(clause->inputcollids,
matching_cols)))
break;
}
if (i >= index->nkeycolumns)
break; /* no match found */
/* Add column number to returned list */
iclause->indexcols = lappend_int(iclause->indexcols, i);
/* Add operator info to lists */
get_op_opfamily_properties(expr_op, index->opfamily[i], false,
&op_strategy,
&op_lefttype,
&op_righttype);
expr_ops = lappend_oid(expr_ops, expr_op);
opfamilies = lappend_oid(opfamilies, index->opfamily[i]);
lefttypes = lappend_oid(lefttypes, op_lefttype);
righttypes = lappend_oid(righttypes, op_righttype);
/* This column matches, keep scanning */
matching_cols++;
}
/* Result is non-lossy if all columns are usable as index quals */
iclause->lossy = (matching_cols != list_length(clause->opnos));
/*
* We can use rinfo->clause as-is if we have var on left and it's all
* usable as index quals.
*/
if (var_on_left && !iclause->lossy)
iclause->indexquals = list_make1(rinfo);
else
{
/*
* We have to generate a modified rowcompare (possibly just one
* OpExpr). The painful part of this is changing < to <= or > to >=,
* so deal with that first.
*/
if (!iclause->lossy)
{
/* very easy, just use the commuted operators */
new_ops = expr_ops;
}
else if (op_strategy == BTLessEqualStrategyNumber ||
op_strategy == BTGreaterEqualStrategyNumber)
{
/* easy, just use the same (possibly commuted) operators */
new_ops = list_truncate(expr_ops, matching_cols);
}
else
{
ListCell *opfamilies_cell;
ListCell *lefttypes_cell;
ListCell *righttypes_cell;
if (op_strategy == BTLessStrategyNumber)
op_strategy = BTLessEqualStrategyNumber;
else if (op_strategy == BTGreaterStrategyNumber)
op_strategy = BTGreaterEqualStrategyNumber;
else
elog(ERROR, "unexpected strategy number %d", op_strategy);
new_ops = NIL;
forthree(opfamilies_cell, opfamilies,
lefttypes_cell, lefttypes,
righttypes_cell, righttypes)
{
Oid opfam = lfirst_oid(opfamilies_cell);
Oid lefttype = lfirst_oid(lefttypes_cell);
Oid righttype = lfirst_oid(righttypes_cell);
expr_op = get_opfamily_member(opfam, lefttype, righttype,
op_strategy);
if (!OidIsValid(expr_op)) /* should not happen */
elog(ERROR, "missing operator %d(%u,%u) in opfamily %u",
op_strategy, lefttype, righttype, opfam);
new_ops = lappend_oid(new_ops, expr_op);
}
}
/* If we have more than one matching col, create a subset rowcompare */
if (matching_cols > 1)
{
RowCompareExpr *rc = makeNode(RowCompareExpr);
rc->rctype = (RowCompareType) op_strategy;
rc->opnos = new_ops;
rc->opfamilies = list_truncate(list_copy(clause->opfamilies),
matching_cols);
rc->inputcollids = list_truncate(list_copy(clause->inputcollids),
matching_cols);
rc->largs = list_truncate(copyObject(var_args),
matching_cols);
rc->rargs = list_truncate(copyObject(non_var_args),
matching_cols);
iclause->indexquals = list_make1(make_simple_restrictinfo((Expr *) rc));
}
else
{
Expr *op;
/* We don't report an index column list in this case */
iclause->indexcols = NIL;
op = make_opclause(linitial_oid(new_ops), BOOLOID, false,
copyObject(linitial(var_args)),
copyObject(linitial(non_var_args)),
InvalidOid,
linitial_oid(clause->inputcollids));
iclause->indexquals = list_make1(make_simple_restrictinfo(op));
}
}
return iclause;
}
/****************************************************************************
* ---- ROUTINES TO CHECK ORDERING OPERATORS ----
****************************************************************************/
/*
* match_pathkeys_to_index
* Test whether an index can produce output ordered according to the
* given pathkeys using "ordering operators".
*
* If it can, return a list of suitable ORDER BY expressions, each of the form
* "indexedcol operator pseudoconstant", along with an integer list of the
* index column numbers (zero based) that each clause would be used with.
* NIL lists are returned if the ordering is not achievable this way.
*
* On success, the result list is ordered by pathkeys, and in fact is
* one-to-one with the requested pathkeys.
*/
static void
match_pathkeys_to_index(IndexOptInfo *index, List *pathkeys,
List **orderby_clauses_p,
List **clause_columns_p)
{
List *orderby_clauses = NIL;
List *clause_columns = NIL;
ListCell *lc1;
*orderby_clauses_p = NIL; /* set default results */
*clause_columns_p = NIL;
/* Only indexes with the amcanorderbyop property are interesting here */
if (!index->amcanorderbyop)
return;
foreach(lc1, pathkeys)
{
PathKey *pathkey = (PathKey *) lfirst(lc1);
bool found = false;
ListCell *lc2;
/*
* Note: for any failure to match, we just return NIL immediately.
* There is no value in matching just some of the pathkeys.
*/
/* Pathkey must request default sort order for the target opfamily */
if (pathkey->pk_strategy != BTLessStrategyNumber ||
pathkey->pk_nulls_first)
return;
/* If eclass is volatile, no hope of using an indexscan */
if (pathkey->pk_eclass->ec_has_volatile)
return;
/*
* Try to match eclass member expression(s) to index. Note that child
* EC members are considered, but only when they belong to the target
* relation. (Unlike regular members, the same expression could be a
* child member of more than one EC. Therefore, the same index could
* be considered to match more than one pathkey list, which is OK
* here. See also get_eclass_for_sort_expr.)
*/
foreach(lc2, pathkey->pk_eclass->ec_members)
{
EquivalenceMember *member = (EquivalenceMember *) lfirst(lc2);
int indexcol;
/* No possibility of match if it references other relations */
if (!bms_equal(member->em_relids, index->rel->relids))
continue;
/*
* We allow any column of the index to match each pathkey; they
* don't have to match left-to-right as you might expect. This is
* correct for GiST, and it doesn't matter for SP-GiST because
* that doesn't handle multiple columns anyway, and no other
* existing AMs support amcanorderbyop. We might need different
* logic in future for other implementations.
*/
for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)
{
Expr *expr;
expr = match_clause_to_ordering_op(index,
indexcol,
member->em_expr,
pathkey->pk_opfamily);
if (expr)
{
orderby_clauses = lappend(orderby_clauses, expr);
clause_columns = lappend_int(clause_columns, indexcol);
found = true;
break;
}
}
if (found) /* don't want to look at remaining members */
break;
}
if (!found) /* fail if no match for this pathkey */
return;
}
*orderby_clauses_p = orderby_clauses; /* success! */
*clause_columns_p = clause_columns;
}
/*
* match_clause_to_ordering_op
* Determines whether an ordering operator expression matches an
* index column.
*
* This is similar to, but simpler than, match_clause_to_indexcol.
* We only care about simple OpExpr cases. The input is a bare
* expression that is being ordered by, which must be of the form
* (indexkey op const) or (const op indexkey) where op is an ordering
* operator for the column's opfamily.
*
* 'index' is the index of interest.
* 'indexcol' is a column number of 'index' (counting from 0).
* 'clause' is the ordering expression to be tested.
* 'pk_opfamily' is the btree opfamily describing the required sort order.
*
* Note that we currently do not consider the collation of the ordering
* operator's result. In practical cases the result type will be numeric
* and thus have no collation, and it's not very clear what to match to
* if it did have a collation. The index's collation should match the
* ordering operator's input collation, not its result.
*
* If successful, return 'clause' as-is if the indexkey is on the left,
* otherwise a commuted copy of 'clause'. If no match, return NULL.
*/
static Expr *
match_clause_to_ordering_op(IndexOptInfo *index,
int indexcol,
Expr *clause,
Oid pk_opfamily)
{
Oid opfamily;
Oid idxcollation;
Node *leftop,
*rightop;
Oid expr_op;
Oid expr_coll;
Oid sortfamily;
bool commuted;
Assert(indexcol < index->nkeycolumns);
opfamily = index->opfamily[indexcol];
idxcollation = index->indexcollations[indexcol];
/*
* Clause must be a binary opclause.
*/
if (!is_opclause(clause))
return NULL;
leftop = get_leftop(clause);
rightop = get_rightop(clause);
if (!leftop || !rightop)
return NULL;
expr_op = ((OpExpr *) clause)->opno;
expr_coll = ((OpExpr *) clause)->inputcollid;
/*
* We can forget the whole thing right away if wrong collation.
*/
if (!IndexCollMatchesExprColl(idxcollation, expr_coll))
return NULL;
/*
* Check for clauses of the form: (indexkey operator constant) or
* (constant operator indexkey).
*/
if (match_index_to_operand(leftop, indexcol, index) &&
!contain_var_clause(rightop) &&
!contain_volatile_functions(rightop))
{
commuted = false;
}
else if (match_index_to_operand(rightop, indexcol, index) &&
!contain_var_clause(leftop) &&
!contain_volatile_functions(leftop))
{
/* Might match, but we need a commuted operator */
expr_op = get_commutator(expr_op);
if (expr_op == InvalidOid)
return NULL;
commuted = true;
}
else
return NULL;
/*
* Is the (commuted) operator an ordering operator for the opfamily? And
* if so, does it yield the right sorting semantics?
*/
sortfamily = get_op_opfamily_sortfamily(expr_op, opfamily);
if (sortfamily != pk_opfamily)
return NULL;
/* We have a match. Return clause or a commuted version thereof. */
if (commuted)
{
OpExpr *newclause = makeNode(OpExpr);
/* flat-copy all the fields of clause */
memcpy(newclause, clause, sizeof(OpExpr));
/* commute it */
newclause->opno = expr_op;
newclause->opfuncid = InvalidOid;
newclause->args = list_make2(rightop, leftop);
clause = (Expr *) newclause;
}
return clause;
}
/****************************************************************************
* ---- ROUTINES TO DO PARTIAL INDEX PREDICATE TESTS ----
****************************************************************************/
/*
* check_index_predicates
* Set the predicate-derived IndexOptInfo fields for each index
* of the specified relation.
*
* predOK is set true if the index is partial and its predicate is satisfied
* for this query, ie the query's WHERE clauses imply the predicate.
*
* indrestrictinfo is set to the relation's baserestrictinfo list less any
* conditions that are implied by the index's predicate. (Obviously, for a
* non-partial index, this is the same as baserestrictinfo.) Such conditions
* can be dropped from the plan when using the index, in certain cases.
*
* At one time it was possible for this to get re-run after adding more
* restrictions to the rel, thus possibly letting us prove more indexes OK.
* That doesn't happen any more (at least not in the core code's usage),
* but this code still supports it in case extensions want to mess with the
* baserestrictinfo list. We assume that adding more restrictions can't make
* an index not predOK. We must recompute indrestrictinfo each time, though,
* to make sure any newly-added restrictions get into it if needed.
*/
void
check_index_predicates(PlannerInfo *root, RelOptInfo *rel)
{
List *clauselist;
bool have_partial;
bool is_target_rel;
Relids otherrels;
ListCell *lc;
/* Indexes are available only on base or "other" member relations. */
Assert(IS_SIMPLE_REL(rel));
/*
* Initialize the indrestrictinfo lists to be identical to
* baserestrictinfo, and check whether there are any partial indexes. If
* not, this is all we need to do.
*/
have_partial = false;
foreach(lc, rel->indexlist)
{
IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
index->indrestrictinfo = rel->baserestrictinfo;
if (index->indpred)
have_partial = true;
}
if (!have_partial)
return;
/*
* Construct a list of clauses that we can assume true for the purpose of
* proving the index(es) usable. Restriction clauses for the rel are
* always usable, and so are any join clauses that are "movable to" this
* rel. Also, we can consider any EC-derivable join clauses (which must
* be "movable to" this rel, by definition).
*/
clauselist = list_copy(rel->baserestrictinfo);
/* Scan the rel's join clauses */
foreach(lc, rel->joininfo)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
/* Check if clause can be moved to this rel */
if (!join_clause_is_movable_to(rinfo, rel))
continue;
clauselist = lappend(clauselist, rinfo);
}
/*
* Add on any equivalence-derivable join clauses. Computing the correct
* relid sets for generate_join_implied_equalities is slightly tricky
* because the rel could be a child rel rather than a true baserel, and in
* that case we must remove its parents' relid(s) from all_baserels.
*/
if (rel->reloptkind == RELOPT_OTHER_MEMBER_REL)
otherrels = bms_difference(root->all_baserels,
find_childrel_parents(root, rel));
else
otherrels = bms_difference(root->all_baserels, rel->relids);
if (!bms_is_empty(otherrels))
clauselist =
list_concat(clauselist,
generate_join_implied_equalities(root,
bms_union(rel->relids,
otherrels),
otherrels,
rel));
/*
* Normally we remove quals that are implied by a partial index's
* predicate from indrestrictinfo, indicating that they need not be
* checked explicitly by an indexscan plan using this index. However, if
* the rel is a target relation of UPDATE/DELETE/SELECT FOR UPDATE, we
* cannot remove such quals from the plan, because they need to be in the
* plan so that they will be properly rechecked by EvalPlanQual testing.
* Some day we might want to remove such quals from the main plan anyway
* and pass them through to EvalPlanQual via a side channel; but for now,
* we just don't remove implied quals at all for target relations.
*/
is_target_rel = (rel->relid == root->parse->resultRelation ||
get_plan_rowmark(root->rowMarks, rel->relid) != NULL);
/*
* Now try to prove each index predicate true, and compute the
* indrestrictinfo lists for partial indexes. Note that we compute the
* indrestrictinfo list even for non-predOK indexes; this might seem
* wasteful, but we may be able to use such indexes in OR clauses, cf
* generate_bitmap_or_paths().
*/
foreach(lc, rel->indexlist)
{
IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
ListCell *lcr;
if (index->indpred == NIL)
continue; /* ignore non-partial indexes here */
if (!index->predOK) /* don't repeat work if already proven OK */
index->predOK = predicate_implied_by(index->indpred, clauselist,
false);
/* If rel is an update target, leave indrestrictinfo as set above */
if (is_target_rel)
continue;
/* Else compute indrestrictinfo as the non-implied quals */
index->indrestrictinfo = NIL;
foreach(lcr, rel->baserestrictinfo)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lcr);
/* predicate_implied_by() assumes first arg is immutable */
if (contain_mutable_functions((Node *) rinfo->clause) ||
!predicate_implied_by(list_make1(rinfo->clause),
index->indpred, false))
index->indrestrictinfo = lappend(index->indrestrictinfo, rinfo);
}
}
}
/****************************************************************************
* ---- ROUTINES TO CHECK EXTERNALLY-VISIBLE CONDITIONS ----
****************************************************************************/
/*
* ec_member_matches_indexcol
* Test whether an EquivalenceClass member matches an index column.
*
* This is a callback for use by generate_implied_equalities_for_column.
*/
static bool
ec_member_matches_indexcol(PlannerInfo *root, RelOptInfo *rel,
EquivalenceClass *ec, EquivalenceMember *em,
void *arg)
{
IndexOptInfo *index = ((ec_member_matches_arg *) arg)->index;
int indexcol = ((ec_member_matches_arg *) arg)->indexcol;
Oid curFamily;
Oid curCollation;
Assert(indexcol < index->nkeycolumns);
curFamily = index->opfamily[indexcol];
curCollation = index->indexcollations[indexcol];
/*
* If it's a btree index, we can reject it if its opfamily isn't
* compatible with the EC, since no clause generated from the EC could be
* used with the index. For non-btree indexes, we can't easily tell
* whether clauses generated from the EC could be used with the index, so
* don't check the opfamily. This might mean we return "true" for a
* useless EC, so we have to recheck the results of
* generate_implied_equalities_for_column; see
* match_eclass_clauses_to_index.
*/
if (index->relam == BTREE_AM_OID &&
!list_member_oid(ec->ec_opfamilies, curFamily))
return false;
/* We insist on collation match for all index types, though */
if (!IndexCollMatchesExprColl(curCollation, ec->ec_collation))
return false;
return match_index_to_operand((Node *) em->em_expr, indexcol, index);
}
/*
* relation_has_unique_index_for
* Determine whether the relation provably has at most one row satisfying
* a set of equality conditions, because the conditions constrain all
* columns of some unique index.
*
* The conditions can be represented in either or both of two ways:
* 1. A list of RestrictInfo nodes, where the caller has already determined
* that each condition is a mergejoinable equality with an expression in
* this relation on one side, and an expression not involving this relation
* on the other. The transient outer_is_left flag is used to identify which
* side we should look at: left side if outer_is_left is false, right side
* if it is true.
* 2. A list of expressions in this relation, and a corresponding list of
* equality operators. The caller must have already checked that the operators
* represent equality. (Note: the operators could be cross-type; the
* expressions should correspond to their RHS inputs.)
*
* The caller need only supply equality conditions arising from joins;
* this routine automatically adds in any usable baserestrictinfo clauses.
* (Note that the passed-in restrictlist will be destructively modified!)
*/
bool
relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel,
List *restrictlist,
List *exprlist, List *oprlist)
{
ListCell *ic;
Assert(list_length(exprlist) == list_length(oprlist));
/* Short-circuit if no indexes... */
if (rel->indexlist == NIL)
return false;
/*
* Examine the rel's restriction clauses for usable var = const clauses
* that we can add to the restrictlist.
*/
foreach(ic, rel->baserestrictinfo)
{
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(ic);
/*
* Note: can_join won't be set for a restriction clause, but
* mergeopfamilies will be if it has a mergejoinable operator and
* doesn't contain volatile functions.
*/
if (restrictinfo->mergeopfamilies == NIL)
continue; /* not mergejoinable */
/*
* The clause certainly doesn't refer to anything but the given rel.
* If either side is pseudoconstant then we can use it.
*/
if (bms_is_empty(restrictinfo->left_relids))
{
/* righthand side is inner */
restrictinfo->outer_is_left = true;
}
else if (bms_is_empty(restrictinfo->right_relids))
{
/* lefthand side is inner */
restrictinfo->outer_is_left = false;
}
else
continue;
/* OK, add to list */
restrictlist = lappend(restrictlist, restrictinfo);
}
/* Short-circuit the easy case */
if (restrictlist == NIL && exprlist == NIL)
return false;
/* Examine each index of the relation ... */
foreach(ic, rel->indexlist)
{
IndexOptInfo *ind = (IndexOptInfo *) lfirst(ic);
int c;
/*
* If the index is not unique, or not immediately enforced, or if it's
* a partial index that doesn't match the query, it's useless here.
*/
if (!ind->unique || !ind->immediate ||
(ind->indpred != NIL && !ind->predOK))
continue;
/*
* Try to find each index column in the lists of conditions. This is
* O(N^2) or worse, but we expect all the lists to be short.
*/
for (c = 0; c < ind->nkeycolumns; c++)
{
bool matched = false;
ListCell *lc;
ListCell *lc2;
foreach(lc, restrictlist)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
Node *rexpr;
/*
* The condition's equality operator must be a member of the
* index opfamily, else it is not asserting the right kind of
* equality behavior for this index. We check this first
* since it's probably cheaper than match_index_to_operand().
*/
if (!list_member_oid(rinfo->mergeopfamilies, ind->opfamily[c]))
continue;
/*
* XXX at some point we may need to check collations here too.
* For the moment we assume all collations reduce to the same
* notion of equality.
*/
/* OK, see if the condition operand matches the index key */
if (rinfo->outer_is_left)
rexpr = get_rightop(rinfo->clause);
else
rexpr = get_leftop(rinfo->clause);
if (match_index_to_operand(rexpr, c, ind))
{
matched = true; /* column is unique */
break;
}
}
if (matched)
continue;
forboth(lc, exprlist, lc2, oprlist)
{
Node *expr = (Node *) lfirst(lc);
Oid opr = lfirst_oid(lc2);
/* See if the expression matches the index key */
if (!match_index_to_operand(expr, c, ind))
continue;
/*
* The equality operator must be a member of the index
* opfamily, else it is not asserting the right kind of
* equality behavior for this index. We assume the caller
* determined it is an equality operator, so we don't need to
* check any more tightly than this.
*/
if (!op_in_opfamily(opr, ind->opfamily[c]))
continue;
/*
* XXX at some point we may need to check collations here too.
* For the moment we assume all collations reduce to the same
* notion of equality.
*/
matched = true; /* column is unique */
break;
}
if (!matched)
break; /* no match; this index doesn't help us */
}
/* Matched all key columns of this index? */
if (c == ind->nkeycolumns)
return true;
}
return false;
}
/*
* indexcol_is_bool_constant_for_query
*
* If an index column is constrained to have a constant value by the query's
* WHERE conditions, then it's irrelevant for sort-order considerations.
* Usually that means we have a restriction clause WHERE indexcol = constant,
* which gets turned into an EquivalenceClass containing a constant, which
* is recognized as redundant by build_index_pathkeys(). But if the index
* column is a boolean variable (or expression), then we are not going to
* see WHERE indexcol = constant, because expression preprocessing will have
* simplified that to "WHERE indexcol" or "WHERE NOT indexcol". So we are not
* going to have a matching EquivalenceClass (unless the query also contains
* "ORDER BY indexcol"). To allow such cases to work the same as they would
* for non-boolean values, this function is provided to detect whether the
* specified index column matches a boolean restriction clause.
*/
bool
indexcol_is_bool_constant_for_query(IndexOptInfo *index, int indexcol)
{
ListCell *lc;
/* If the index isn't boolean, we can't possibly get a match */
if (!IsBooleanOpfamily(index->opfamily[indexcol]))
return false;
/* Check each restriction clause for the index's rel */
foreach(lc, index->rel->baserestrictinfo)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
/*
* As in match_clause_to_indexcol, never match pseudoconstants to
* indexes. (It might be semantically okay to do so here, but the
* odds of getting a match are negligible, so don't waste the cycles.)
*/
if (rinfo->pseudoconstant)
continue;
/* See if we can match the clause's expression to the index column */
if (match_boolean_index_clause(rinfo, indexcol, index))
return true;
}
return false;
}
/****************************************************************************
* ---- ROUTINES TO CHECK OPERANDS ----
****************************************************************************/
/*
* match_index_to_operand()
* Generalized test for a match between an index's key
* and the operand on one side of a restriction or join clause.
*
* operand: the nodetree to be compared to the index
* indexcol: the column number of the index (counting from 0)
* index: the index of interest
*
* Note that we aren't interested in collations here; the caller must check
* for a collation match, if it's dealing with an operator where that matters.
*
* This is exported for use in selfuncs.c.
*/
bool
match_index_to_operand(Node *operand,
int indexcol,
IndexOptInfo *index)
{
int indkey;
/*
* Ignore any RelabelType node above the operand. This is needed to be
* able to apply indexscanning in binary-compatible-operator cases. Note:
* we can assume there is at most one RelabelType node;
* eval_const_expressions() will have simplified if more than one.
*/
if (operand && IsA(operand, RelabelType))
operand = (Node *) ((RelabelType *) operand)->arg;
indkey = index->indexkeys[indexcol];
if (indkey != 0)
{
/*
* Simple index column; operand must be a matching Var.
*/
if (operand && IsA(operand, Var) &&
index->rel->relid == ((Var *) operand)->varno &&
indkey == ((Var *) operand)->varattno)
return true;
}
else
{
/*
* Index expression; find the correct expression. (This search could
* be avoided, at the cost of complicating all the callers of this
* routine; doesn't seem worth it.)
*/
ListCell *indexpr_item;
int i;
Node *indexkey;
indexpr_item = list_head(index->indexprs);
for (i = 0; i < indexcol; i++)
{
if (index->indexkeys[i] == 0)
{
if (indexpr_item == NULL)
elog(ERROR, "wrong number of index expressions");
indexpr_item = lnext(index->indexprs, indexpr_item);
}
}
if (indexpr_item == NULL)
elog(ERROR, "wrong number of index expressions");
indexkey = (Node *) lfirst(indexpr_item);
/*
* Does it match the operand? Again, strip any relabeling.
*/
if (indexkey && IsA(indexkey, RelabelType))
indexkey = (Node *) ((RelabelType *) indexkey)->arg;
if (equal(indexkey, operand))
return true;
}
return false;
}
/*
* is_pseudo_constant_for_index()
* Test whether the given expression can be used as an indexscan
* comparison value.
*
* An indexscan comparison value must not contain any volatile functions,
* and it can't contain any Vars of the index's own table. Vars of
* other tables are okay, though; in that case we'd be producing an
* indexqual usable in a parameterized indexscan. This is, therefore,
* a weaker condition than is_pseudo_constant_clause().
*
* This function is exported for use by planner support functions,
* which will have available the IndexOptInfo, but not any RestrictInfo
* infrastructure. It is making the same test made by functions above
* such as match_opclause_to_indexcol(), but those rely where possible
* on RestrictInfo information about variable membership.
*
* expr: the nodetree to be checked
* index: the index of interest
*/
bool
is_pseudo_constant_for_index(Node *expr, IndexOptInfo *index)
{
/* pull_varnos is cheaper than volatility check, so do that first */
if (bms_is_member(index->rel->relid, pull_varnos(expr)))
return false; /* no good, contains Var of table */
if (contain_volatile_functions(expr))
return false; /* no good, volatile comparison value */
return true;
}