这篇文章主要讲解了“PostgreSQL物理优化中的create_index_paths->generate_bitmap_or_paths函数分析”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“PostgreSQL物理优化中的create_index_paths->generate_bitmap_or_paths函数分析”吧！
该函数从条件子句链表中寻找OR子句,如找到并且可以处理则生成BitmapOrPath。
下面是BitmapOrPath访问路径样例:
testdb=# explain verbose select t1.* from t_dwxx t1 where (dwbh > '10000' and dwbh < '30000') OR (dwdz between 'DWDZ10000' and 'DWDZ20000'); QUERY PLAN --------------------------------------------------------------------------------------------- Bitmap Heap Scan on public.t_dwxx t1 (cost=84.38..216.82 rows=3156 width=20) Output: dwmc, dwbh, dwdz Recheck Cond: ((((t1.dwbh)::text > '10000'::text) AND ((t1.dwbh)::text < '30000'::text)) OR (((t1.dwdz)::text >= 'DWDZ1000 0'::text) AND ((t1.dwdz)::text <= 'DWDZ20000'::text))) -> BitmapOr (cost=84.38..84.38 rows=3422 width=0) -->BitmapOr -> Bitmap Index Scan on t_dwxx_pkey (cost=0.00..50.52 rows=2223 width=0) Index Cond: (((t1.dwbh)::text > '10000'::text) AND ((t1.dwbh)::text < '30000'::text)) -> Bitmap Index Scan on idx_dwxx_dwdz (cost=0.00..32.28 rows=1200 width=0) Index Cond: (((t1.dwdz)::text >= 'DWDZ10000'::text) AND ((t1.dwdz)::text <= 'DWDZ20000'::text)) (8 rows)
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!
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
generate_bitmap_or_paths函数
create_index_paths->generate_bitmap_or_paths函数从条件子句链表中寻找OR子句,如找到并且可以处理则生成BitmapOrPath.函数返回生成的链表BitmapOrPaths.
/*
* 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.
* 从条件子句链表中寻找OR子句,如找到并且可以处理则生成BitmapOrPath.
* 函数返回生成的链表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.)
* other_clauses是一个附加子句链表，
* 为了生成索引条件，可以假定为true，但不能用于搜索OR子句。
*/
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.
* 使用当前和其他子句作为build_paths_for_OR函数的输入参数
* 从而不需要从列表中删除OR子句。
*/
all_clauses = list_concat(list_copy(clauses), other_clauses);//合并到链表中
foreach(lc, clauses)//遍历子句链表
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);//约束条件
List *pathlist;//路径链表
Path *bitmapqual;//
ListCell *j;
/* Ignore RestrictInfos that aren't ORs */
if (!restriction_is_or_clause(rinfo))//不是OR子句,处理下一个子句
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.
* 必须能够将至少一个索引匹配到OR的某个分支，否则无法使用索引。
*/
pathlist = NIL;
foreach(j, ((BoolExpr *) rinfo->orclause)->args)//遍历OR子句参数
{
Node *orarg = (Node *) lfirst(j);//参数节点
List *indlist;
/* OR arguments should be ANDs or sub-RestrictInfos */
//OR子句的参数必须是AND子句或者是子约束条件
if (and_clause(orarg))//如为AND子句
{
List *andargs = ((BoolExpr *) orarg)->args;//获取AND子句的参数
indlist = build_paths_for_OR(root, rel,
andargs,
all_clauses);//构建路径
/* Recurse in case there are sub-ORs */
//递归调用generate_bitmap_or_paths,并添加到访问路径链表中
indlist = list_concat(indlist,
generate_bitmap_or_paths(root, rel,
andargs,
all_clauses));
}
else
{
RestrictInfo *rinfo = castNode(RestrictInfo, orarg);//不是AND,则为约束条件
List *orargs;
Assert(!restriction_is_or_clause(rinfo));
orargs = list_make1(rinfo);
indlist = build_paths_for_OR(root, rel,
orargs,
all_clauses);//构建访问路径
}
/*
* If nothing matched this arm, we can't do anything with this OR
* clause.
*/
if (indlist == NIL)
{
pathlist = NIL;
break;
}
/*
* OK, pick the most promising AND combination, and add it to
* pathlist.
* 选择最有希望的组合，并将其添加到路径列表中。
*/
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.
* 如果左右两边都匹配，那么将它们转换为BitmapOrPath，并添加到结果列表中。
*/
if (pathlist != NIL)
{
//创建BitmapOrPath
bitmapqual = (Path *) create_bitmap_or_path(root, rel, pathlist);
result = lappend(result, bitmapqual);
}
}
return result;
}
//------------------------------------------------------ build_paths_for_OR
/*
* build_paths_for_OR
* Given a list of restriction clauses from one arm of an OR clause,
* construct all matching IndexPaths for the relation.
* 给定OR子句的约束条件子句,构建该Relation所有匹配的索引访问路径.
*
* Here we must scan all indexes of the relation, since a bitmap OR tree
* can use multiple indexes.
* BitmapOr可能会使用多个索引,因此需要访问该Relation的所有索引.
*
* 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.
* 函数调用方提供了2个约束条件子句链表,一个是"current",另外一个是"other".
* 这两个链表都可以用于资源匹配索引键,但是索引必须使用至少一个存在于"current"中的子句.
* 举个例子,有下面的条件语句:
* WHERE (x = 42) AND (... OR (y = 52 AND z = 77) OR ....)
* 在考察OR中的x/z子句时,可以使用"x = 42"作为可用的索引条件,但
* 但不应该将子句单独与x上的任何索引进行匹配，因为这样的访问路径已经在上层生成。
* 因此可以在OR子句上使用x,y,z上索引或x,y上的索引,但不能是x上的索引.
* 在处理部分索引时,与索引谓词匹配的"current"子句同样可以使用此索引.
*
* '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
* 输入参数:
* rel-需要生成访问路径的Relation
* clauses-"current"子句,节点类型为RestrictInfo
* other_clauses-"other"子句,上层子句已处理
*/
static List *
build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
List *clauses, List *other_clauses)
{
List *result = NIL;//返回结果
List *all_clauses = NIL; /* not computed till needed */
ListCell *lc;//临时变量
foreach(lc, rel->indexlist)//遍历RelOptInfo上的Index
{
IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);//IndexOptInfo
IndexClauseSet clauseset;//
List *indexpaths;
bool useful_predicate;
/* Ignore index if it doesn't support bitmap scans */
if (!index->amhasgetbitmap)//索引不支持BitmapIndexScan
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.
* 忽略不匹配查询的部分索引。如predOK标记为T,则可考虑使用此索引.
* 否则，必须测试添加的子句是否足以包含索引谓词.
* 在这种情况下才可以在当前上下文中使用索引。
*
* 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.)
* 如验证通过,则将useful_predicate设置为T。
* 这是为了避免predOK索引与OR的某个分支相匹配，这是一个合法但无意义的低效计划。
* (只需要扫描部分索引就可以产生一个更好的计划，但不是OR子句)
*/
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(list_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.
* 标记与索引匹配的约束条件子句
*/
MemSet(&clauseset, 0, sizeof(clauseset));
match_clauses_to_index(index, clauses, &clauseset);
/*
* If no matches so far, and the index predicate isn't useful, we
* don't want it.
*/
if (!clauseset.nonempty && !useful_predicate)//没有合适的,继续下一个索引
continue;
/*
* Add "other" restriction clauses to the clauseset.
*/
match_clauses_to_index(index, other_clauses, &clauseset);//添加到clauseset中
/*
* Construct paths if possible.
*/
indexpaths = build_index_paths(root, rel,
index, &clauseset,
useful_predicate,
ST_BITMAPSCAN,
NULL,
NULL);//构建索引访问路径
result = list_concat(result, indexpaths);
}
return result;
}
//------------------------------------------------------ create_bitmap_or_path
/*
* create_bitmap_or_path
* Creates a path node representing a BitmapOr.
* 创建BitmapOr路径节点
*/
BitmapOrPath *
create_bitmap_or_path(PlannerInfo *root,
RelOptInfo *rel,
List *bitmapquals)
{
BitmapOrPath *pathnode = makeNode(BitmapOrPath);
pathnode->path.pathtype = T_BitmapOr;
pathnode->path.parent = rel;
pathnode->path.pathtarget = rel->reltarget;
pathnode->path.param_info = NULL; /* not used in bitmap trees */
/*
* Currently, a BitmapHeapPath, BitmapAndPath, or BitmapOrPath will be
* parallel-safe if and only if rel->consider_parallel is set. So, we can
* set the flag for this path based only on the relation-level flag,
* without actually iterating over the list of children.
*/
pathnode->path.parallel_aware = false;
pathnode->path.parallel_safe = rel->consider_parallel;
pathnode->path.parallel_workers = 0;
pathnode->path.pathkeys = NIL; /* always unordered */
pathnode->bitmapquals = bitmapquals;
/* this sets bitmapselectivity as well as the regular cost fields: */
cost_bitmap_or_node(pathnode, root);//计算成本
return pathnode;
}
//------------------------------------ create_bitmap_or_path
/*
* cost_bitmap_or_node
* Estimate the cost of a BitmapOr node
* 估算BitmapOr成本
*
* See comments for cost_bitmap_and_node.
*/
void
cost_bitmap_or_node(BitmapOrPath *path, PlannerInfo *root)
{
Cost totalCost;
Selectivity selec;
ListCell *l;
/*
* We estimate OR selectivity on the assumption that the inputs are
* non-overlapping, since that's often the case in "x IN (list)" type
* situations. Of course, we clamp to 1.0 at the end.
* 我们估算或计算选择率的前提是输入不重叠，因为存在“x in (list)”这样的情况。
* 当然，我们在最后调整为1.0。
*
* The runtime cost of the BitmapOr itself is estimated at 100x
* cpu_operator_cost for each tbm_union needed. Probably too small,
* definitely too simplistic? We are aware that the tbm_unions are
* optimized out when the inputs are BitmapIndexScans.
* 对于所需的每个tbm_union操作,
* BitmapOr本身的运行时成本估计为100 x cpu_operator_cost。
* 这个估值是否太小，太简单了?其实，当输入是位图索引扫描时，tbm_unions已被优化。
*/
totalCost = 0.0;//成本
selec = 0.0;//选择率
foreach(l, path->bitmapquals)//遍历条件
{
Path *subpath = (Path *) lfirst(l);//路径
Cost subCost;//成本
Selectivity subselec;
cost_bitmap_tree_node(subpath, &subCost, &subselec);//遍历路径获取成本&选择率
selec += subselec;//
totalCost += subCost;
if (l != list_head(path->bitmapquals) &&
!IsA(subpath, IndexPath))
totalCost += 100.0 * cpu_operator_cost;//非单个条件而且不是索引访问路径,则添加运行期成本
}
path->bitmapselectivity = Min(selec, 1.0);//选择率
path->path.rows = 0; /* per above, not used */
path->path.startup_cost = totalCost;
path->path.total_cost = totalCost;
}测试脚本如下
select t1.* from t_dwxx t1 where (dwbh > '10000' and dwbh < '30000') OR (dwdz between 'DWDZ10000' and 'DWDZ20000');
启动gdb跟踪
(gdb) b generate_bitmap_or_paths Breakpoint 1 at 0x74e6c1: file indxpath.c, line 1266. (gdb) c Continuing. Breakpoint 1, generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0) at indxpath.c:1266 1266 List *result = NIL;
查看输入参数,clauses是链表,只有一个元素(BoolExpr类型,即OR子句);other_clauses为NULL
(gdb) p *clauses
$1 = {type = T_List, length = 1, head = 0x2aaf118, tail = 0x2aaf118}
(gdb) p *(Node *)clauses->head->data.ptr_value
$2 = {type = T_RestrictInfo}
(gdb) p *(RestrictInfo *)clauses->head->data.ptr_value
$3 = {type = T_RestrictInfo, clause = 0x2aad818, is_pushed_down = true, outerjoin_delayed = false, can_join = false,
pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x2aaf100, required_relids = 0x2aae938,
outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x0, right_relids = 0x0, orclause = 0x2aaefc0, parent_ec = 0x0,
eval_cost = {startup = 0, per_tuple = 0.01}, norm_selec = 0.31556115090433856, outer_selec = -1, mergeopfamilies = 0x0,
left_ec = 0x0, right_ec = 0x0, left_em = 0x0, right_em = 0x0, scansel_cache = 0x0, outer_is_left = false,
hashjoinoperator = 0, left_bucketsize = -1, right_bucketsize = -1, left_mcvfreq = -1, right_mcvfreq = -1}
(gdb) p *((RestrictInfo *)clauses->head->data.ptr_value)->clause
$4 = {type = T_BoolExpr}
(gdb) set $clause=((RestrictInfo *)clauses->head->data.ptr_value)->clause
(gdb) p *(BoolExpr *)$clause
$6 = {xpr = {type = T_BoolExpr}, boolop = OR_EXPR, args = 0x2aad758, location = -1}遍历clausees子句,rinfo->clause即BoolExpr(OR子句)
... 1276 foreach(lc, clauses) (gdb) 1278 RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc); (gdb) 1284 if (!restriction_is_or_clause(rinfo))
遍历OR子句的参数
(gdb) 1292 foreach(j, ((BoolExpr *) rinfo->orclause)->args)
参数的第一个元素,BoolExpr,boolop操作符为AND_EXPR
(gdb) n
1294 Node *orarg = (Node *) lfirst(j);
(gdb)
1298 if (and_clause(orarg))
(gdb) p *orarg
$10 = {type = T_BoolExpr}
(gdb) p *(BoolExpr *)orarg
$11 = {xpr = {type = T_BoolExpr}, boolop = AND_EXPR, args = 0x2aaea90, location = -1}AND子句的参数
(gdb) n
1300 List *andargs = ((BoolExpr *) orarg)->args;
(gdb)
1302 indlist = build_paths_for_OR(root, rel,
(gdb) p *andargs
$12 = {type = T_List, length = 2, head = 0x2aada78, tail = 0x2aada98}
(gdb) p *(Node *)andargs->head->data.ptr_value
$13 = {type = T_RestrictInfo}
(gdb) p *(RestrictInfo *)andargs->head->data.ptr_value
$14 = {type = T_RestrictInfo, clause = 0x2aace08, is_pushed_down = true, outerjoin_delayed = false, can_join = false,
pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x2aaea78, required_relids = 0x2aaea78,
outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x2aaea60, right_relids = 0x0, orclause = 0x0, parent_ec = 0x0,
eval_cost = {startup = 0, per_tuple = 0.0025000000000000001}, norm_selec = 0.99990000000000001, outer_selec = -1,
mergeopfamilies = 0x0, left_ec = 0x0, right_ec = 0x0, left_em = 0x0, right_em = 0x0, scansel_cache = 0x0,
outer_is_left = false, hashjoinoperator = 0, left_bucketsize = -1, right_bucketsize = -1, left_mcvfreq = -1,
right_mcvfreq = -1}
(gdb) p *((RestrictInfo *)andargs->head->data.ptr_value)->clause
$15 = {type = T_OpExpr}
(gdb) set $tmp=((RestrictInfo *)andargs->head->data.ptr_value)->clause
(gdb) p *(OpExpr *)$tmp
$16 = {xpr = {type = T_OpExpr}, opno = 666, opfuncid = 742, opresulttype = 16, opretset = false, opcollid = 0,
inputcollid = 100, args = 0x2aacd68, location = 39}
(gdb) set $tmp2=((RestrictInfo *)andargs->head->next->data.ptr_value)->clause
(gdb) p *(OpExpr *)$tmp2
$17 = {xpr = {type = T_OpExpr}, opno = 664, opfuncid = 740, opresulttype = 16, opretset = false, opcollid = 0,
inputcollid = 100, args = 0x2aacc78, location = 58}
(gdb)进入build_paths_for_OR函数
(gdb) step build_paths_for_OR (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaea90, other_clauses=0x2aaf598) at indxpath.c:1170 1170 List *result = NIL;
遍历索引,第一个索引是idx_dwxx_dwdz
1174 foreach(lc, rel->indexlist)
(gdb)
1176 IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
(gdb)
1182 if (!index->amhasgetbitmap)
(gdb) p *index
$18 = {type = T_IndexOptInfo, indexoid = 16753, reltablespace = 0, rel = 0x2aa6658, pages = 40, tuples = 10000,
tree_height = 1, ncolumns = 1, nkeycolumns = 1, indexkeys = 0x2aae590, indexcollations = 0x2aae5a8, opfamily = 0x2aae5c0,
opcintype = 0x2aae5d8, sortopfamily = 0x2aae5c0, reverse_sort = 0x2aae608, nulls_first = 0x2aae620,
canreturn = 0x2aae5f0, relam = 403, indexprs = 0x0, indpred = 0x0, indextlist = 0x2aae6f8, indrestrictinfo = 0x2aaf138,
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>}
--
testdb=# select relname from pg_class where oid=16753;
relname
---------------
idx_dwxx_dwdz
(1 row)
--与约束条件不匹配((dwbh > '10000' and dwbh < '30000')),继续下一个索引
1229 if (!clauseset.nonempty && !useful_predicate)
(gdb) p clauseset
$20 = {nonempty = false, indexclauses = {0x0 <repeats 32 times>}}
(gdb) n
1230 continue;下一个索引是idx_dwxx_predicate_dwmc/idx_dwxx_expr,同样不匹配,继续寻找索引,直至索引t_dwxx_pkey
(gdb) p *index
$23 = {type = T_IndexOptInfo, indexoid = 16738,...
1223 match_clauses_to_index(index, clauses, &clauseset);
(gdb)
1229 if (!clauseset.nonempty && !useful_predicate)
(gdb) p clauseset
$24 = {nonempty = true, indexclauses = {0x2aaf638, 0x0 <repeats 31 times>}}构建索引访问路径
(gdb)
1246 result = list_concat(result, indexpaths);
(gdb) p *indexpaths
$25 = {type = T_List, length = 1, head = 0x2aafb48, tail = 0x2aafb48}
(gdb) p *(Node *)indexpaths->head->data.ptr_value
$26 = {type = T_IndexPath}
(gdb) p *(IndexPath *)indexpaths->head->data.ptr_value
$27 = {path = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 3156, startup_cost = 0.28500000000000003,
total_cost = 191.46871600907946, pathkeys = 0x0}, indexinfo = 0x2aa6868, indexclauses = 0x2aaf6a8,
indexquals = 0x2aaf898, indexqualcols = 0x2aaf8e8, indexorderbys = 0x0, indexorderbycols = 0x0,
indexscandir = ForwardScanDirection, indextotalcost = 50.515000000000001, indexselectivity = 0.22227191011235958}回到generate_bitmap_or_paths函数
1250 } (gdb) generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0) at indxpath.c:1307 1307 indlist = list_concat(indlist,
递归进入generate_bitmap_or_paths
(gdb) n Breakpoint 1, generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaea90, other_clauses=0x2aaf598) at indxpath.c:1266 1266 List *result = NIL; #直接结束 (gdb) finish Run till exit from #0 generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaea90, other_clauses=0x2aaf598) at indxpath.c:1266 0x000000000074e7a0 in generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0) at indxpath.c:1307 1307 indlist = list_concat(indlist, Value returned is $28 = (List *) 0x0
完成第一轮循环
(gdb) n
1329 if (indlist == NIL)
(gdb) n
1339 bitmapqual = choose_bitmap_and(root, rel, indlist);
(gdb)
1340 pathlist = lappend(pathlist, bitmapqual);
(gdb) p *bitmapqual
$29 = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 3156, startup_cost = 0.28500000000000003,
total_cost = 191.46871600907946, pathkeys = 0x0}这是第二个AND子句
1292 foreach(j, ((BoolExpr *) rinfo->orclause)->args) (gdb) 1294 Node *orarg = (Node *) lfirst(j); (gdb) 1298 if (and_clause(orarg)) (gdb) 1300 List *andargs = ((BoolExpr *) orarg)->args;
完成第二轮循环
(gdb)
1339 bitmapqual = choose_bitmap_and(root, rel, indlist);
(gdb)
1340 pathlist = lappend(pathlist, bitmapqual);
(gdb) p bitmapqual
$33 = (Path *) 0x2aafd78
(gdb) p *bitmapqual
$34 = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 3156, startup_cost = 0.28500000000000003,
total_cost = 148.08735471522883, pathkeys = 0x0}结束循环,构建BitmapOrPath
1347 if (pathlist != NIL) (gdb) 1349 bitmapqual = (Path *) create_bitmap_or_path(root, rel, pathlist);
进入create_bitmap_or_path,调用函数cost_bitmap_or_node计算成本
(gdb) step create_bitmap_or_path (root=0x2aa6248, rel=0x2aa6658, bitmapquals=0x2aafbf8) at pathnode.c:1156 1156 BitmapOrPath *pathnode = makeNode(BitmapOrPath); ... 1178 cost_bitmap_or_node(pathnode, root); (gdb) step cost_bitmap_or_node (path=0x2ab0278, root=0x2aa6248) at costsize.c:1149 ...
计算结果,与执行计划中的信息相匹配"BitmapOr (cost=84.38..84.38 rows=3422 width=0)"
(gdb) p *path
$37 = {path = {type = T_BitmapOrPath, pathtype = T_BitmapOr, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 0, startup_cost = 84.378,
total_cost = 84.378, pathkeys = 0x0}, bitmapquals = 0x2aafbf8, bitmapselectivity = 0.34222288270157986}回到generate_bitmap_or_paths
(gdb) n create_bitmap_or_path (root=0x2aa6248, rel=0x2aa6658, bitmapquals=0x2aafbf8) at pathnode.c:1180 1180 return pathnode; (gdb) 1181 } (gdb) generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0) at indxpath.c:1350 1350 result = lappend(result, bitmapqual);
感谢各位的阅读，以上就是“PostgreSQL物理优化中的create_index_paths->generate_bitmap_or_paths函数分析”的内容了，经过本文的学习后，相信大家对PostgreSQL物理优化中的create_index_paths->generate_bitmap_or_paths函数分析这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！
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