这篇文章主要介绍“PostgreSQL中set_base_rel_pathlists函数有什么作用”，在日常操作中，相信很多人在PostgreSQL中set_base_rel_pathlists函数有什么作用问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”PostgreSQL中set_base_rel_pathlists函数有什么作用”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
set_base_rel_pathlists函数的目的是为每一个base rel找出所有可用的访问路径(包括顺序扫描和所有可用的索引)，每一个可用的路径都会添加到pathlist链表中。
一、数据结构
RelOptInfo
typedef struct RelOptInfo
{
NodeTag type;//节点标识
RelOptKind reloptkind;//RelOpt类型
/* all relations included in this RelOptInfo */
Relids relids; /*Relids(rtindex)集合 set of base relids (rangetable indexes) */
/* size estimates generated by planner */
double rows; /*结果元组的估算数量 estimated number of result tuples */
/* per-relation planner control flags */
bool consider_startup; /*是否考虑启动成本?是,需要保留启动成本低的路径 keep cheap-startup-cost paths? */
bool consider_param_startup; /*是否考虑参数化?的路径 ditto, for parameterized paths? */
bool consider_parallel; /*是否考虑并行处理路径 consider parallel paths? */
/* default result targetlist for Paths scanning this relation */
struct PathTarget *reltarget; /*扫描该Relation时默认的结果 list of Vars/Exprs, cost, width */
/* materialization information */
List *pathlist; /*访问路径链表 Path structures */
List *ppilist; /*路径链表中使用参数化路径进行 ParamPathInfos used in pathlist */
List *partial_pathlist; /* partial Paths */
struct Path *cheapest_startup_path;//代价最低的启动路径
struct Path *cheapest_total_path;//代价最低的整体路径
struct Path *cheapest_unique_path;//代价最低的获取唯一值的路径
List *cheapest_parameterized_paths;//代价最低的参数化路径链表
/* parameterization information needed for both base rels and join rels */
/* (see also lateral_vars and lateral_referencers) */
Relids direct_lateral_relids; /*使用lateral语法,需依赖的Relids rels directly laterally referenced */
Relids lateral_relids; /* minimum parameterization of rel */
/* information about a base rel (not set for join rels!) */
//reloptkind=RELOPT_BASEREL时使用的数据结构
Index relid; /* Relation ID */
Oid reltablespace; /* 表空间 containing tablespace */
RTEKind rtekind; /* 基表?子查询?还是函数等等?RELATION, SUBQUERY, FUNCTION, etc */
AttrNumber min_attr; /* 最小的属性编号 smallest attrno of rel (often <0) */
AttrNumber max_attr; /* 最大的属性编号 largest attrno of rel */
Relids *attr_needed; /* 数组 array indexed [min_attr .. max_attr] */
int32 *attr_widths; /* 属性宽度 array indexed [min_attr .. max_attr] */
List *lateral_vars; /* 关系依赖的Vars/PHVs LATERAL Vars and PHVs referenced by rel */
Relids lateral_referencers; /*依赖该关系的Relids rels that reference me laterally */
List *indexlist; /* 该关系的IndexOptInfo链表 list of IndexOptInfo */
List *statlist; /* 统计信息链表 list of StatisticExtInfo */
BlockNumber pages; /* 块数 size estimates derived from pg_class */
double tuples; /* 元组数 */
double allvisfrac; /* ? */
PlannerInfo *subroot; /* 如为子查询,存储子查询的root if subquery */
List *subplan_params; /* 如为子查询,存储子查询的参数 if subquery */
int rel_parallel_workers; /* 并行执行,需要多少个workers? wanted number of parallel workers */
/* Information about foreign tables and foreign joins */
//FDW相关信息
Oid serverid; /* identifies server for the table or join */
Oid userid; /* identifies user to check access as */
bool useridiscurrent; /* join is only valid for current user */
/* use "struct FdwRoutine" to avoid including fdwapi.h here */
struct FdwRoutine *fdwroutine;
void *fdw_private;
/* cache space for remembering if we have proven this relation unique */
//已知的,可保证唯一元组返回的Relids链表
List *unique_for_rels; /* known unique for these other relid
* set(s) */
List *non_unique_for_rels; /* 已知的,返回的数据不唯一的Relids链表 known not unique for these set(s) */
/* used by various scans and joins: */
List *baserestrictinfo; /* 如为基本关系,则存储约束条件 RestrictInfo structures (if base rel) */
QualCost baserestrictcost; /* 解析约束表达式的成本? cost of evaluating the above */
Index baserestrict_min_security; /* 最低安全等级 min security_level found in
* baserestrictinfo */
List *joininfo; /* 连接语句的约束条件信息 RestrictInfo structures for join clauses
* involving this rel */
bool has_eclass_joins; /* 是否存在等价类连接? True意味着joininfo并不完整,,T means joininfo is incomplete */
/* used by partitionwise joins: */
//是否尝试partitionwise连接,这是PG 11的一个新特性.
bool consider_partitionwise_join; /* consider partitionwise
* join paths? (if
* partitioned rel) */
Relids top_parent_relids; /* Relids of topmost parents (if "other"
* rel) */
/* used for partitioned relations */
//分区表使用
PartitionScheme part_scheme; /* 分区的schema Partitioning scheme. */
int nparts; /* 分区数 number of partitions */
struct PartitionBoundInfoData *boundinfo; /* 分区边界信息 Partition bounds */
List *partition_qual; /* 分区约束 partition constraint */
struct RelOptInfo **part_rels; /* 分区的RelOptInfo数组 Array of RelOptInfos of partitions,
* stored in the same order of bounds */
List **partexprs; /* 非空分区键表达式 Non-nullable partition key expressions. */
List **nullable_partexprs; /* 可为空的分区键表达式 Nullable partition key expressions. */
List *partitioned_child_rels; /* RT Indexes链表 List of RT indexes. */
} RelOptInfo;
Cost相关
注意:实际使用的参数值通过系统配置文件定义,而不是这里的常量定义!
/*
* The cost estimate produced by cost_qual_eval() includes both a one-time
* (startup) cost, and a per-tuple cost.
*/
typedef struct QualCost
{
Cost startup; /* 启动成本,one-time cost */
Cost per_tuple; /* 每个元组的成本,per-evaluation cost */
} QualCost;
typedef double Cost; /* execution cost (in page-access units) */
/* defaults for costsize.c's Cost parameters */
/* NB: cost-estimation code should use the variables, not these constants! */
/* 注意:实际值通过系统配置文件定义,而不是这里的常量定义! */
/* If you change these, update backend/utils/misc/postgresql.sample.conf */
#define DEFAULT_SEQ_PAGE_COST 1.0 //顺序扫描page的成本
#define DEFAULT_RANDOM_PAGE_COST 4.0 //随机扫描page的成本
#define DEFAULT_CPU_TUPLE_COST 0.01 //处理一个元组的CPU成本
#define DEFAULT_CPU_INDEX_TUPLE_COST 0.005 //处理一个索引元组的CPU成本
#define DEFAULT_CPU_OPERATOR_COST 0.0025 //执行一次操作或函数的CPU成本
#define DEFAULT_PARALLEL_TUPLE_COST 0.1 //并行执行,从一个worker传输一个元组到另一个worker的成本
#define DEFAULT_PARALLEL_SETUP_COST 1000.0 //构建并行执行环境的成本
#define DEFAULT_EFFECTIVE_CACHE_SIZE 524288 /*先前已有介绍, measured in pages */
double seq_page_cost = DEFAULT_SEQ_PAGE_COST;
double random_page_cost = DEFAULT_RANDOM_PAGE_COST;
double cpu_tuple_cost = DEFAULT_CPU_TUPLE_COST;
double cpu_index_tuple_cost = DEFAULT_CPU_INDEX_TUPLE_COST;
double cpu_operator_cost = DEFAULT_CPU_OPERATOR_COST;
double parallel_tuple_cost = DEFAULT_PARALLEL_TUPLE_COST;
double parallel_setup_cost = DEFAULT_PARALLEL_SETUP_COST;
int effective_cache_size = DEFAULT_EFFECTIVE_CACHE_SIZE;
Cost disable_cost = 1.0e10;//1后面10个0,通过设置一个巨大的成本,让优化器自动放弃此路径
int max_parallel_workers_per_gather = 2;//每次gather使用的worker数
IndexClauseSet
用于收集匹配索引的的条件语句
/* Data structure for collecting qual clauses that match an index */
typedef struct
{
bool nonempty; /* True if lists are not all empty */
/* Lists of RestrictInfos, one per index column */
List *indexclauses[INDEX_MAX_KEYS];
} IndexClauseSet;
二、源码解读
set_base_rel_pathlists函数遍历RelOptInfo数组,为每一个Rel构造访问路径,先前已介绍了顺序扫描的成本估算,本节介绍索引扫描的成本估算(函数:create_index_paths),通过调用set_plain_rel_pathlist->create_index_paths函数实现.
/*
* set_plain_rel_pathlist
* Build access paths for a plain relation (no subquery, no inheritance)
*/
static void
set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
Relids required_outer;
//...
/* 索引扫描,Consider index scans */
create_index_paths(root, rel);
/* TID扫描,Consider TID scans */
create_tidscan_paths(root, rel);
}
create_index_paths
create_index_paths函数生成Relation所有可能被选中的索引访问路径,详见源码注释.
/*
* create_index_paths()
* Generate all interesting index paths for the given relation.
* Candidate paths are added to the rel's pathlist (using add_path).
* 生成Relation所有可能被选中的索引访问路径.
* Paths通过add_path方法加入到RelOptInfo的pathlist链表中.
*
* 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.
* 使用索引扫描的前提是:1.索引必须匹配一个或多个限制条件或连接条件,或者
* 2.匹配查询的ORDER BY排序条件,或者3.匹配查询条件的谓词(部分/条件索引)
*
* 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.
* 有两种基本的索引扫描类型,一种是"plain"索引扫描,只使用限制条件(或者什么都
* 没有),这种扫描方法适用于任何场景.另外一种是"parameterized"扫描,使用连接条件
* (可能的话,加上限制条件)."parameterized"扫描只能出现在嵌套循环中的内关系中,
* 因为参数由外关系提供.
*
* 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.
* IndexPath访问路径通过函数add_path生成并提交.
*
* 输入参数:
* 'rel' is the relation for which we want to generate index paths
* rel是待生成索引范围路径的关系
*
* Note: check_index_predicates() must have been run previously for this rel.
* 注意:函数check_index_predicates在调用此函数前调用
*
* 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".
*/
void
create_index_paths(PlannerInfo *root, RelOptInfo *rel)
{
List *indexpaths;//索引访问路径链表
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)//不存在索引,退出
return;
/* Bitmap paths are collected and then dealt with at the end */
bitindexpaths = bitjoinpaths = joinorclauses = NIL;//初始赋值
/* Examine each index in turn */
foreach(lc, rel->indexlist)//遍历索引链表
{
IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);//索引信息
/* Protect limited-size array in IndexClauseSets */
Assert(index->ncolumns <= 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.)
*/
if (index->indpred != NIL && !index->predOK)//部分索引,而且不能使用,不使用此索引
continue;
/*
* Identify the restriction clauses that can match the index.
* 验证索引和条件是否匹配
*/
MemSet(&rclauseset, 0, sizeof(rclauseset));
match_restriction_clauses_to_index(rel, 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.
* 通过限制条件创建非参数化索引访问路径.Plain访问路径通过函数add_path直接添加到RelOptInfo中
* 位图访问路径添加到bitindexpaths链表中,后续再处理
*/
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.
* 验证索引是否与连接条件匹配(连接条件与限制条件相互独立).
* 这一步只是发现未被合并到EC中的"loose"连接条件,在此之后会收集连接中的OR条件
*/
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.
* 通过EC(等价类)匹配索引,结果存储在eclauseset链表中
*/
MemSet(&eclauseset, 0, sizeof(eclauseset));
match_eclass_clauses_to_index(root, index,
&eclauseset);
/*
* If we found any plain or eclass join clauses, build parameterized
* index paths using them.
* 如果存在plain或者eclass连接条件,创建参数化索引访问路径
*/
if (jclauseset.nonempty || eclauseset.nonempty)
consider_index_join_clauses(root, rel, index,
&rclauseset,
&jclauseset,
&eclauseset,
&bitjoinpaths);
}
/*
* Generate BitmapOrPaths for any suitable OR-clauses present in the
* restriction list. Add these to bitindexpaths.
* 基于RelOptInfo中的限制条件生成BitmapOrPaths访问路径
*/
indexpaths = generate_bitmap_or_paths(root, rel,
rel->baserestrictinfo, NIL);
bitindexpaths = list_concat(bitindexpaths, indexpaths);//合并到bitindexpaths链表中
/*
* Likewise, generate BitmapOrPaths for any suitable OR-clauses present in
* the joinclause list. Add these to bitjoinpaths.
* 同样的,基于连接条件joinorclause中的OR语句生成BitmapOrPaths访问路径
*/
indexpaths = generate_bitmap_or_paths(root, rel,
joinorclauses, rel->baserestrictinfo);
bitjoinpaths = list_concat(bitjoinpaths, indexpaths);//合并到bitjoinpaths链表中
/*
* 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)//存在位图索引访问路径
{
Path *bitmapqual;//访问路径
BitmapHeapPath *bpath;//BitmapHeapPath访问路径
bitmapqual = choose_bitmap_and(root, rel, bitindexpaths);//位图表达式路径
bpath = create_bitmap_heap_path(root, rel, bitmapqual,
rel->lateral_relids, 1.0, 0);//BitmapHeapPath访问路径
add_path(rel, (Path *) bpath);//添加到RelOptInfo中
/* create a partial bitmap heap path */
if (rel->consider_parallel && rel->lateral_relids == NULL)
create_partial_bitmap_paths(root, rel, bitmapqual);//创建并行访问路径
}
/*
* 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)//bitjoinpaths位图连接访问路径
{
List *path_outer;//依赖的外部Relids链表
List *all_path_outers;//依赖的外部路径Relids链表
ListCell *lc;//临时变量
/*
* path_outer holds the parameterization of each path in bitjoinpaths
* (to save recalculating that several times), while all_path_outers
* holds all distinct parameterization sets.
*/
path_outer = all_path_outers = NIL;//初始化变量
foreach(lc, bitjoinpaths)//遍历bitjoinpaths
{
Path *path = (Path *) lfirst(lc);//访问路径
Relids required_outer;//依赖的外部Relids
required_outer = get_bitmap_tree_required_outer(path);//
path_outer = lappend(path_outer, required_outer);//添加到链表中
if (!bms_equal_any(required_outer, all_path_outers))//不等,则添加到all_path_outers中
all_path_outers = lappend(all_path_outers, required_outer);
}
/* Now, for each distinct parameterization set ... */
//对每一个唯一的参数化集合进行处理
foreach(lc, all_path_outers)//遍历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;
ListCell *lco;
/* Identify all the bitmap join paths needing no more than that */
this_path_set = NIL;
forboth(lcp, bitjoinpaths, lco, path_outer)//遍历
{
Path *path = (Path *) lfirst(lcp);
Relids p_outers = (Relids) lfirst(lco);
if (bms_is_subset(p_outers, max_outers))//无需依赖其他Relids,添加到this_path_set中
this_path_set = lappend(this_path_set, path);
}
/*
* Add in restriction bitmap paths, since they can be used
* together with any join paths.
*/
this_path_set = list_concat(this_path_set, bitindexpaths);//合并bitindexpaths访问路径
/* Select best AND combination for this parameterization */
bitmapqual = choose_bitmap_and(root, rel, this_path_set);//为此参数化处理选择最好的AND组合
/* And push that path into the mix */
required_outer = get_bitmap_tree_required_outer(bitmapqual);
loop_count = get_loop_count(root, rel->relid, required_outer);
bpath = create_bitmap_heap_path(root, rel, bitmapqual,
required_outer, loop_count, 0);//创建索引访问路径
add_path(rel, (Path *) bpath);
}
}
}
match_XXX
match_restriction_clauses_to_index函数验证限制条件是否与Index匹配,匹配的条件添加到clauseset中.
match_join_clauses_to_index函数验证连接条件是否与Index匹配,同样的,匹配的条件添加到clauseset中.
match_eclass_clauses_to_index函数验证EC连接条件是否与Index匹配,匹配的条件添加到clauseset中.
//--------------------------------------------------- match_restriction_clauses_to_index
/*
* match_restriction_clauses_to_index
* Identify restriction clauses for the rel that match the index.
* Matching clauses are added to *clauseset.
* 验证限制条件是否与Index匹配,匹配的条件加入到clauseset中
*/
static void
match_restriction_clauses_to_index(RelOptInfo *rel, IndexOptInfo *index,
IndexClauseSet *clauseset)
{
/* We can ignore clauses that are implied by the index predicate */
//忽略部分(条件)索引,直接调用match_clauses_to_index
match_clauses_to_index(index, index->indrestrictinfo, clauseset);
}
//------------------------------- match_clauses_to_index
/*
* 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(IndexOptInfo *index,
List *clauses,
IndexClauseSet *clauseset)
{
ListCell *lc;//临时变量
foreach(lc, clauses)//遍历限制条件
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
match_clause_to_index(index, rinfo, clauseset);
}
}
//--------------------------------------------------- match_join_clauses_to_index
/*
* 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.
* 验证连接条件是否与Index匹配,匹配的条件添加到clauseset中
* 另外,在joinorclauses中添加可能有用的连接条件OR子句
*/
static void
match_join_clauses_to_index(PlannerInfo *root,
RelOptInfo *rel, IndexOptInfo *index,
IndexClauseSet *clauseset,
List **joinorclauses)
{
ListCell *lc;//临时变量
/* Scan the rel's join clauses */
foreach(lc, rel->joininfo)//遍历连接条件
{
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(index, rinfo, clauseset);
}
}
//--------------------------------------------------- match_eclass_clauses_to_index
/*
* match_eclass_clauses_to_index
* Identify EquivalenceClass join clauses for the rel that match the index.
* Matching clauses are added to *clauseset.
* 验证EC连接条件是否与Index匹配,相匹配的子句加入到clauseset中
*/
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)//没有ECs,返回
return;
for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)//遍历索引列
{
ec_member_matches_arg arg;
List *clauses;
/* Generate clauses, skipping any that join to lateral_referencers */
//生成条件子句链表
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(index, clauses, clauseset);
}
}
//---------------------------- generate_implied_equalities_for_column
/*
* generate_implied_equalities_for_column
* Create EC-derived joinclauses usable with a specific column.
* 创建可用于特定列的EC衍生连接条件
*
* This is used by indxpath.c to extract potentially indexable joinclauses
* from ECs, and can be used by foreign data wrappers for similar purposes.
* We assume that only expressions in Vars of a single table are of interest,
* but the caller provides a callback function to identify exactly which
* such expressions it would like to know about.
*
* We assume that any given table/index column could appear in only one EC.
* (This should be true in all but the most pathological cases, and if it
* isn't, we stop on the first match anyway.) Therefore, what we return
* is a redundant list of clauses equating the table/index column to each of
* the other-relation values it is known to be equal to. Any one of
* these clauses can be used to create a parameterized path, and there
* is no value in using more than one. (But it *is* worthwhile to create
* a separate parameterized path for each one, since that leads to different
* join orders.)
*
* The caller can pass a Relids set of rels we aren't interested in joining
* to, so as to save the work of creating useless clauses.
*/
List *
generate_implied_equalities_for_column(PlannerInfo *root,
RelOptInfo *rel,
ec_matches_callback_type callback,
void *callback_arg,
Relids prohibited_rels)
{
List *result = NIL;//结果链表
bool is_child_rel = (rel->reloptkind == RELOPT_OTHER_MEMBER_REL);//是否子Relation
Relids parent_relids;//父Relids
ListCell *lc1;//变量
/* Indexes are available only on base or "other" member relations. */
Assert(IS_SIMPLE_REL(rel));
/* If it's a child rel, we'll need to know what its parent(s) are */
if (is_child_rel)
parent_relids = find_childrel_parents(root, rel);
else
parent_relids = NULL; /* not used, but keep compiler quiet */
foreach(lc1, root->eq_classes)//遍历EC
{
EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);//当前的EC
EquivalenceMember *cur_em;//EC成员
ListCell *lc2;//链表成员
/*
* Won't generate joinclauses if const or single-member (the latter
* test covers the volatile case too)
*/
if (cur_ec->ec_has_const || list_length(cur_ec->ec_members) <= 1)
continue;
/*
* No point in searching if rel not mentioned in eclass (but we can't
* tell that for a child rel).
*/
if (!is_child_rel &&
!bms_is_subset(rel->relids, cur_ec->ec_relids))
continue;
/*
* Scan members, looking for a match to the target column. 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, it's
* potentially order-dependent which EC a child relation's target
* column gets matched to. This is annoying but it only happens in
* corner cases, so for now we live with just reporting the first
* match. See also get_eclass_for_sort_expr.)
*/
cur_em = NULL;
foreach(lc2, cur_ec->ec_members)//遍历EC的成员
{
cur_em = (EquivalenceMember *) lfirst(lc2);//当前成员
if (bms_equal(cur_em->em_relids, rel->relids) &&
callback(root, rel, cur_ec, cur_em, callback_arg))//调用ec_member_matches_indexcol函数
break;//找到匹配的成员,跳出
cur_em = NULL;
}
if (!cur_em)
continue;
/*
* Found our match. Scan the other EC members and attempt to generate
* joinclauses.
*/
foreach(lc2, cur_ec->ec_members)
{
EquivalenceMember *other_em = (EquivalenceMember *) lfirst(lc2);
Oid eq_op;
RestrictInfo *rinfo;
if (other_em->em_is_child)//
continue; /* 忽略子成员,ignore children here */
/* Make sure it'll be a join to a different rel */
if (other_em == cur_em ||
bms_overlap(other_em->em_relids, rel->relids))//过滤cur_em
continue;
/* Forget it if caller doesn't want joins to this rel */
if (bms_overlap(other_em->em_relids, prohibited_rels))
continue;
/*
* Also, if this is a child rel, avoid generating a useless join
* to its parent rel(s).
*/
if (is_child_rel &&
bms_overlap(parent_relids, other_em->em_relids))
continue;
eq_op = select_equality_operator(cur_ec,
cur_em->em_datatype,
other_em->em_datatype);
if (!OidIsValid(eq_op))
continue;
/* set parent_ec to mark as redundant with other joinclauses */
rinfo = create_join_clause(root, cur_ec, eq_op,
cur_em, other_em,
cur_ec);//创建连接条件语句
result = lappend(result, rinfo);
}
/*
* If somehow we failed to create any join clauses, we might as well
* keep scanning the ECs for another match. But if we did make any,
* we're done, because we don't want to return non-redundant clauses.
*/
if (result)
break;
}
return result;
}
//---------------------------- match_clause_to_index
/*
* match_clause_to_index
* Test whether a qual clause can be used with an index.
*
* If the clause is usable, add 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(IndexOptInfo *index,
RestrictInfo *rinfo,
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++)
{
if (match_clause_to_indexcol(index,
indexcol,
rinfo))
{
clauseset->indexclauses[indexcol] =
list_append_unique_ptr(clauseset->indexclauses[indexcol],
rinfo);//赋值
clauseset->nonempty = true;//设置标记
return;
}
}
}
//------------------- match_clause_to_indexcol
/*
* match_clause_to_indexcol()
* Determines whether a restriction clause matches a column of an index.
* 判断约束条件是否与索引中的某一列匹配
*
* To match an index normally, the clause:
* 通常来说,匹配索引,子句必须:
* (1) must be in the form (indexkey op const) or (const op indexkey);
* and
* 满足格式:(索引键 操作符 常量) 或者 (常量 操作符 索引键),而且
* (2) must contain an operator which is in the same family as the index
* operator for this column, or is a "special" operator as recognized
* by match_special_index_operator();
* and
* 包含一种与索引列同一family的操作符,或者是一种通过
match_special_index_operator方法认定的特殊操作符
* (3) must match the collation of the index, if collation is relevant.
* 与索引的排序规则collation匹配
*
* 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.
* 这里"const"常量的定义非常自由:除了易变函数或索引关系的Var之外的,均视为"const"
* 由于存在参数化索引扫描的可能,因此查询中属于其他Relations的Vars也可以在此出现.
* 调用此函数的代码有责任"合适"的管理限制条件和连接条件.
*
* 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.
* 注意:需要在子句的const部分检查索引关系的Vars，因为子句
* 如(a.f1 OP (b.f2 OP a.f3)不能通过a上的参数化索引扫描进行处理
*
* 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 do not actually do the commuting here, but we check whether a
* suitable commutator operator is available.
* 目前为止,执行器只能处理索引键在左边的索引表达式,因此只能使用那些可以
* 把索引键变换到左边的条件表达式.在这个函数中不执行变换,但会执行相应的检查.
*
* 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.)
* 如果索引含有排序规则(collation),条件子句必须包含相同的排序规则.
* 对于无collation的索引,假定collation没有任何影响.
*
* It is also possible to match RowCompareExpr clauses to indexes (but
* currently, only btree indexes handle this). In this routine we will
* report a match if 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 --- whether the
* remaining columns match the index too is considered in
* adjust_rowcompare_for_index().
* RowCompareExpr有可能与索引进行匹配,在这个处理过程中,如果行对比的第一个列
* 与目标索引匹配,那么可以认为是匹配的.
*
* It is also possible to match ScalarArrayOpExpr clauses to indexes, when
* the clause is of the form "indexkey op ANY (arrayconst)".
* 如果子句的格式是"indexkey op ANY (arrayconst)",那么匹配ScalarArrayOpExpr
* 也是可能的.
*
* For boolean indexes, it is also possible to match the clause directly
* to the indexkey; or perhaps the clause is (NOT indexkey).
* 对于布尔索引,可以直接与索引键进行匹配
*
* 输入参数:
* 'index' is the index of interest.
* index-正在处理的索引
* 'indexcol' is a column number of 'index' (counting from 0).
* indexcol-索引列(从0起算)
* 'rinfo' is the clause to be tested (as a RestrictInfo node).
* rinfo-RestrictInfo Node
*
* Returns true if the clause can be used with this index key.
* 如可以使用索引,则返回T
*
* NOTE: returns false if clause is an OR or AND clause; it is the
* responsibility of higher-level routines to cope with those.
* 注意:如果条件语句是OR/AND语句,则返回F,由上层处理逻辑处理
*/
static bool
match_clause_to_indexcol(IndexOptInfo *index,
int indexcol,
RestrictInfo *rinfo)
{
Expr *clause = rinfo->clause;//条件语句
Index index_relid = index->rel->relid;//Index的Relid
Oid opfamily;//操作符种类
Oid idxcollation;//索引排序规则
Node *leftop,//左节点
*rightop;//右节点
Relids left_relids;//左节点相关Relids
Relids right_relids;//右节点相关Relids
Oid expr_op;//表达式操作符的Oid
Oid expr_coll;//表达式Collation的Oid
bool plain_op;//是否Plain操作符
Assert(indexcol < index->nkeycolumns);
opfamily = index->opfamily[indexcol];//获取操作符种类
idxcollation = index->indexcollations[indexcol];//获取索引排序规则
/* First check for boolean-index cases. */
if (IsBooleanOpfamily(opfamily))//是否布尔类
{
if (match_boolean_index_clause((Node *) clause, indexcol, index))//是否匹配
return true;//如匹配,返回T
}
/*
* Clause must be a binary opclause, or possibly a ScalarArrayOpExpr
* (which is always binary, by definition). Or it could be a
* RowCompareExpr, which we pass off to match_rowcompare_to_indexcol().
* Or, if the index supports it, we can handle IS NULL/NOT NULL clauses.
*/
if (is_opclause(clause))//OpExpr
{
leftop = get_leftop(clause);
rightop = get_rightop(clause);
if (!leftop || !rightop)
return false;
left_relids = rinfo->left_relids;
right_relids = rinfo->right_relids;
expr_op = ((OpExpr *) clause)->opno;
expr_coll = ((OpExpr *) clause)->inputcollid;
plain_op = true;
}
else if (clause && IsA(clause, ScalarArrayOpExpr))//ScalarArrayOpExpr
{
ScalarArrayOpExpr *saop = (ScalarArrayOpExpr *) clause;
/* We only accept ANY clauses, not ALL */
if (!saop->useOr)
return false;
leftop = (Node *) linitial(saop->args);
rightop = (Node *) lsecond(saop->args);
left_relids = NULL; /* not actually needed */
right_relids = pull_varnos(rightop);
expr_op = saop->opno;
expr_coll = saop->inputcollid;
plain_op = false;
}
else if (clause && IsA(clause, RowCompareExpr))//RowCompareExpr
{
return match_rowcompare_to_indexcol(index, indexcol,
opfamily, idxcollation,
(RowCompareExpr *) clause);
}
else if (index->amsearchnulls && IsA(clause, NullTest))//NullTest
{
NullTest *nt = (NullTest *) clause;
if (!nt->argisrow &&
match_index_to_operand((Node *) nt->arg, indexcol, index))
return true;
return false;
}
else
return false;
/*
* Check for clauses of the form: (indexkey operator constant) or
* (constant operator indexkey). See above notes about const-ness.
* (indexkey operator constant)和(constant operator indexkey)格式的语句
*/
//处理:(indexkey operator constant)
if (match_index_to_operand(leftop, indexcol, index) &&
!bms_is_member(index_relid, right_relids) &&
!contain_volatile_functions(rightop))
{
if (IndexCollMatchesExprColl(idxcollation, expr_coll) &&
is_indexable_operator(expr_op, opfamily, true))//排序规则&操作符种类匹配
return true;//返回T
/*
* If we didn't find a member of the index's opfamily, see whether it
* is a "special" indexable operator.
*/
if (plain_op &&
match_special_index_operator(clause, opfamily,
idxcollation, true))//Plain操作&特殊操作符,返回T
return true;
return false;//否则,返回F
}
//处理(constant operator indexkey)
if (plain_op &&
match_index_to_operand(rightop, indexcol, index) &&
!bms_is_member(index_relid, left_relids) &&
!contain_volatile_functions(leftop))
{
if (IndexCollMatchesExprColl(idxcollation, expr_coll) &&
is_indexable_operator(expr_op, opfamily, false))
return true;
/*
* If we didn't find a member of the index's opfamily, see whether it
* is a "special" indexable operator.
*/
if (match_special_index_operator(clause, opfamily,
idxcollation, false))
return true;
return false;
}
return false;
}
三、跟踪分析
测试脚本如下
select a.*,b.grbh,b.je from t_dwxx a, lateral (select t1.dwbh,t1.grbh,t2.je from t_grxx t1 inner join t_jfxx t2 on t1.dwbh = a.dwbh and t1.grbh = t2.grbh) b where a.dwbh = '1001' order by b.dwbh;
注意:按先前的分析,SQL语句存在等价类{t_dwxx.dwbh t_grxx.dwbh '1001'}和{t_grxx.grbh t_jfxx.grbh},在构造t_grxx的索引访问路径时,使用等价类构造.
启动gdb,第一个RelOptInfo(对应t_dwxx)有3个Index,第二个RelOptInfo(对应t_grxx)有2个Index(分别是在dwbh和grbh上的索引),第三个RelOptInfo(对应t_jfxx)有1个Index(grbh上的索引),本节以t_jfxx和t_grxx为例进行跟踪分析
...
(gdb) c
Continuing.
Breakpoint 1, create_index_paths (root=0x2714c50, rel=0x2729530) at indxpath.c:242
242 if (rel->indexlist == NIL)
(gdb) p *(IndexOptInfo *)rel->indexlist->head->data.ptr_value
$38 = {type = T_IndexOptInfo, indexoid = 16750, reltablespace = 0, rel = 0x2729530, pages = 276, tuples = 100000,
tree_height = 1, ncolumns = 1, nkeycolumns = 1, indexkeys = 0x2729998, indexcollations = 0x27299b0, opfamily = 0x27299c8,
opcintype = 0x27299e0, sortopfamily = 0x27299c8, reverse_sort = 0x2729a10, nulls_first = 0x2729a28,
canreturn = 0x27299f8, relam = 403, indexprs = 0x0, indpred = 0x0, indextlist = 0x2729ae0, indrestrictinfo = 0x0,
predOK = false, unique = false, immediate = true, hypothetical = false, amcanorderbyop = false, amoptionalkey = true,
amsearcharray = true, amsearchnulls = true, amhasgettuple = true, amhasgetbitmap = true, amcanparallel = true,
amcostestimate = 0x94f0ad <btcostestimate>}
输入信息是已熟知的root(PlannerInfo)和rel(RelOptInfo).首先进行索引遍历循环
(gdb) c
Continuing.
Breakpoint 1, create_index_paths (root=0x2714c50, rel=0x2729530) at indxpath.c:242
242 if (rel->indexlist == NIL)
(gdb) p *(IndexOptInfo *)rel->indexlist->head->data.ptr_value
$38 = {type = T_IndexOptInfo, indexoid = 16750, reltablespace = 0, rel = 0x2729530, pages = 276, tuples = 100000,
tree_height = 1, ncolumns = 1, nkeycolumns = 1, indexkeys = 0x2729998, indexcollations = 0x27299b0, opfamily = 0x27299c8,
opcintype = 0x27299e0, sortopfamily = 0x27299c8, reverse_sort = 0x2729a10, nulls_first = 0x2729a28,
canreturn = 0x27299f8, relam = 403, indexprs = 0x0, indpred = 0x0, indextlist = 0x2729ae0, indrestrictinfo = 0x0,
predOK = false, unique = false, immediate = true, hypothetical = false, amcanorderbyop = false, amoptionalkey = true,
amsearcharray = true, amsearchnulls = true, amhasgettuple = true, amhasgetbitmap = true, amcanparallel = true,
amcostestimate = 0x94f0ad <btcostestimate>}
查询数据字典pg_class,oid=16750相应的索引是idx_t_jfxx_grbh
testdb=# select relname from pg_class where oid=16750; relname ----------------- idx_t_jfxx_grbh (1 row)
调用match_restriction_clauses_to_index和match_join_clauses_to_index,子句集合均为NULL
(gdb)
match_restriction_clauses_to_index (rel=0x2729530, index=0x2729888, clauseset=0x7fff69cf0890) at indxpath.c:2117
2117 }
(gdb)
create_index_paths (root=0x2714c50, rel=0x2729530) at indxpath.c:275
275 get_index_paths(root, rel, index, &rclauseset,
(gdb)
284 MemSet(&jclauseset, 0, sizeof(jclauseset));
(gdb)
285 match_join_clauses_to_index(root, rel, index,
(gdb)
292 MemSet(&eclauseset, 0, sizeof(eclauseset));
(gdb)
293 match_eclass_clauses_to_index(root, index,
(gdb) p rclauseset
$2 = {nonempty = false, indexclauses = {0x0 <repeats 32 times>}}
(gdb) p joinorclauses
$3 = (List *) 0x0
(gdb) p jclauseset
$4 = {nonempty = false, indexclauses = {0x0 <repeats 32 times>}}
进入match_eclass_clauses_to_index
... 268 match_restriction_clauses_to_index(rel, index, &rclauseset); (gdb) step match_restriction_clauses_to_index (rel=0x2724c88, index=0x27254d8, clauseset=0x7fff69cf0890) at indxpath.c:2116 2116 match_clauses_to_index(index, index->indrestrictinfo, clauseset);
进入generate_implied_equalities_for_column
... (gdb) step generate_implied_equalities_for_column (root=0x2714c50, rel=0x2729530, callback=0x7509b0 <ec_member_matches_indexcol>, callback_arg=0x7fff69cf0620, prohibited_rels=0x0) at equivclass.c:2219 2219 List *result = NIL;
等价类信息
...
2235 EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
(gdb)
2243 if (cur_ec->ec_has_const || list_length(cur_ec->ec_members) <= 1)
(gdb) p *cur_ec
$6 = {type = T_EquivalenceClass, ec_opfamilies = 0x272a268, ec_collation = 100, ec_members = 0x272a4a8,
ec_sources = 0x272a3f0, ec_derives = 0x272d2f0, ec_relids = 0x272a470, ec_has_const = false, ec_has_volatile = false,
ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0}
遍历EC的成员后,cur_em不为NULL,查看cur_em内存结构(匹配的成员,即t_jfxx.grbh)
2281 foreach(lc2, cur_ec->ec_members)
(gdb) p *cur_em
$7 = {type = T_EquivalenceMember, em_expr = 0x2722890, em_relids = 0x272a238, em_nullable_relids = 0x0,
em_is_const = false, em_is_child = false, em_datatype = 25}
(gdb) p *cur_em->em_expr
$8 = {type = T_RelabelType}
(gdb) p *(RelabelType *)cur_em->em_expr
$9 = {xpr = {type = T_RelabelType}, arg = 0x2722840, resulttype = 25, resulttypmod = -1, resultcollid = 100,
relabelformat = COERCE_IMPLICIT_CAST, location = -1}
(gdb) p *((RelabelType *)cur_em->em_expr)->arg
$10 = {type = T_Var}
(gdb) p *(Var *)((RelabelType *)cur_em->em_expr)->arg
$11 = {xpr = {type = T_Var}, varno = 4, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 4, varoattno = 1, location = 168}
再次遍历等价类的成员,得到第一个约束条件(t_jfxx.grbh=t_grxx.grbh)
(gdb) n
2314 rinfo = create_join_clause(root, cur_ec, eq_op,
(gdb)
2318 result = lappend(result, rinfo);
(gdb) p *rinfo
$18 = {type = T_RestrictInfo, clause = 0x272d910, is_pushed_down = true, outerjoin_delayed = false, can_join = true,
pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x272db10, required_relids = 0x272d5f0,
outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x272dae0, right_relids = 0x272daf8, orclause = 0x0,
parent_ec = 0x272a340, eval_cost = {startup = 0, per_tuple = 0.0025000000000000001}, norm_selec = -1, outer_selec = -1,
mergeopfamilies = 0x272db48, left_ec = 0x272a340, right_ec = 0x272a340, left_em = 0x272a4d8, right_em = 0x272a420,
scansel_cache = 0x0, outer_is_left = false, hashjoinoperator = 98, left_bucketsize = -1, right_bucketsize = -1,
left_mcvfreq = -1, right_mcvfreq = -1}
(gdb) set $tmp1=(RelabelType *)((OpExpr *)rinfo->clause)->args->head->data.ptr_value
(gdb) set $tmp2=(RelabelType *)((OpExpr *)rinfo->clause)->args->head->next->data.ptr_value
(gdb) p *(Var *)$tmp1->arg
$31 = {xpr = {type = T_Var}, varno = 4, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 4, varoattno = 1, location = 168}
(gdb) p *(Var *)$tmp2->arg
$32 = {xpr = {type = T_Var}, varno = 3, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 3, varoattno = 2, location = 158}
获得了结果,返回到match_eclass_clauses_to_index
2281 foreach(lc2, cur_ec->ec_members) (gdb) 2326 if (result) (gdb) 2327 break; (gdb) 2330 return result; (gdb) 2331 } (gdb) match_eclass_clauses_to_index (root=0x2714c50, index=0x2729888, clauseset=0x7fff69cf0670) at indxpath.c:2184 2184 match_clauses_to_index(index, clauses, clauseset); ...
下面再考察t_grxx.dwbh上的索引为例,分析match_clause_to_index
(gdb) c
Continuing.
Breakpoint 1, create_index_paths (root=0x2714c50, rel=0x2728c38) at indxpath.c:242
242 if (rel->indexlist == NIL)
(gdb) p *(IndexOptInfo *)rel->indexlist->head->data.ptr_value
$39 = {type = T_IndexOptInfo, indexoid = 16752, reltablespace = 0, rel = 0x2728c38, pages = 276, tuples = 100000,
tree_height = 1, ncolumns = 1, nkeycolumns = 1, indexkeys = 0x2729378, indexcollations = 0x2729390, opfamily = 0x27293a8,
opcintype = 0x27293c0, sortopfamily = 0x27293a8, reverse_sort = 0x27293f0, nulls_first = 0x2729408,
canreturn = 0x27293d8, relam = 403, indexprs = 0x0, indpred = 0x0, indextlist = 0x27294e0, indrestrictinfo = 0x272b040,
predOK = false, unique = false, immediate = true, hypothetical = false, amcanorderbyop = false, amoptionalkey = true,
amsearcharray = true, amsearchnulls = true, amhasgettuple = true, amhasgetbitmap = true, amcanparallel = true,
amcostestimate = 0x94f0ad <btcostestimate>}
oid=16752,对应的object为idx_t_grxx_dwbh
testdb=# select relname from pg_class where oid=16752; relname ----------------- idx_t_grxx_dwbh (1 row)
进入IndexOptInfo循环,第一个元素对应的IndexOptInfo为idx_t_grxx_dwbh
249 foreach(lc, rel->indexlist)
(gdb) p *rel->indexlist
$40 = {type = T_List, length = 2, head = 0x2729510, tail = 0x2729218}
(gdb) p *(IndexOptInfo *)rel->indexlist->head->data->ptr_value
$42 = {type = T_IndexOptInfo, indexoid = 16752, reltablespace = 0, rel = 0x2728c38, pages = 276, tuples = 100000,
tree_height = 1, ncolumns = 1, nkeycolumns = 1, indexkeys = 0x2729378, indexcollations = 0x2729390, opfamily = 0x27293a8,
opcintype = 0x27293c0, sortopfamily = 0x27293a8, reverse_sort = 0x27293f0, nulls_first = 0x2729408,
canreturn = 0x27293d8, relam = 403, indexprs = 0x0, indpred = 0x0, indextlist = 0x27294e0, indrestrictinfo = 0x272b040,
predOK = false, unique = false, immediate = true, hypothetical = false, amcanorderbyop = false, amoptionalkey = true,
amsearcharray = true, amsearchnulls = true, amhasgettuple = true, amhasgetbitmap = true, amcanparallel = true,
amcostestimate = 0x94f0ad <btcostestimate>}
一路小跑,进入match_clause_to_indexcol
... (gdb) step match_clause_to_indexcol (index=0x2729268, indexcol=0, rinfo=0x272ae58) at indxpath.c:2330 2330 Expr *clause = rinfo->clause; (gdb) n 2331 Index index_relid = index->rel->relid; (gdb) n 2344 opfamily = index->opfamily[indexcol]; (gdb) 2345 idxcollation = index->indexcollations[indexcol]; (gdb) p index_relid $47 = 3 (gdb) p opfamily $48 = 1994 (gdb)
根据opfamily查询数据字典
testdb=# select * from pg_opfamily where oid=1994; opfmethod | opfname | opfnamespace | opfowner -----------+----------+--------------+---------- 403 | text_ops | 11 | 10 (1 row) -- 索引访问方法(btree) testdb=# select * from pg_am where oid=403; amname | amhandler | amtype --------+-----------+-------- btree | bthandler | i (1 row)
下面进入is_opclause判断分支
(gdb) p idxcollation
$49 = 100
(gdb) n
2360 if (is_opclause(clause))
(gdb)
2362 leftop = get_leftop(clause);
(gdb)
2363 rightop = get_rightop(clause);
(gdb)
2364 if (!leftop || !rightop)
(gdb) p *leftop
$50 = {type = T_RelabelType}
(gdb) p *rightop
$51 = {type = T_Const}
限制条件下推后,形成限制条件t_grxx.dwbh = '1001'
#Var:t_grxx.dwbh
(gdb) p *(RelabelType *)leftop
$56 = {xpr = {type = T_RelabelType}, arg = 0x272ad80, resulttype = 25, resulttypmod = -1, resultcollid = 100,
relabelformat = COERCE_IMPLICIT_CAST, location = -1}
#常量:'1001'
(gdb) p *(Const *)rightop
$57 = {xpr = {type = T_Const}, consttype = 25, consttypmod = -1, constcollid = 100, constlen = -1, constvalue = 41069848,
constisnull = false, constbyval = false, location = 194}
执行相关判断,返回T
(gdb) n 2366 left_relids = rinfo->left_relids; (gdb) 2367 right_relids = rinfo->right_relids; (gdb) 2368 expr_op = ((OpExpr *) clause)->opno; (gdb) 2369 expr_coll = ((OpExpr *) clause)->inputcollid; (gdb) 2370 plain_op = true; (gdb) 2409 if (match_index_to_operand(leftop, indexcol, index) && (gdb) 2410 !bms_is_member(index_relid, right_relids) && (gdb) 2409 if (match_index_to_operand(leftop, indexcol, index) && (gdb) 2411 !contain_volatile_functions(rightop)) (gdb) 2410 !bms_is_member(index_relid, right_relids) && (gdb) 2413 if (IndexCollMatchesExprColl(idxcollation, expr_coll) && (gdb) 2414 is_indexable_operator(expr_op, opfamily, true)) (gdb) 2413 if (IndexCollMatchesExprColl(idxcollation, expr_coll) && (gdb) 2415 return true;
给clauseset变量赋值
(gdb) match_clause_to_index (index=0x2729268, rinfo=0x272ae58, clauseset=0x7fff69cf0890) at indxpath.c:2255 2255 list_append_unique_ptr(clauseset->indexclauses[indexcol], (gdb) 2254 clauseset->indexclauses[indexcol] = (gdb) 2257 clauseset->nonempty = true; (gdb) 2258 return; (gdb) 2261 }
返回到match_clauses_to_index
(gdb) match_clauses_to_index (index=0x2729268, clauses=0x272b040, clauseset=0x7fff69cf0890) at indxpath.c:2200 2200 foreach(lc, clauses)
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原创文章，作者：kirin，如若转载，请注明出处：https://blog.ytso.com/205227.html