PostgreSQL 原始碼解讀（59）- 查詢語句#44（make_one_rel函式#9-B...
本小節繼續介紹查詢物理最佳化中的create_index_paths->generate_bitmap_or_paths函式,該函式從條件子句連結串列中尋找OR子句,如找到並且可以處理則生成BitmapOrPath。
關於Bitmap Scan的相關知識,請參照PostgreSQL DBA(6) - SeqScan vs IndexScan vs BitmapHeapScan這篇文章。
下面是BitmapOrPath訪問路徑樣例:
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)
一、資料結構
Cost相關
注意:實際使用的引數值透過系統配置檔案定義,而不是這裡的常量定義!
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:實際值透過系統配置檔案定義,而不是這裡的常量定義! */
/* If you change these, update backend/utils/misc/postgresql.sample.conf */
#define DEFAULT_SEQ_PAGE_COST 1.0 //順序掃描page的成本
#define DEFAULT_RANDOM_PAGE_COST 4.0 //隨機掃描page的成本
#define DEFAULT_CPU_TUPLE_COST 0.01 //處理一個元組的CPU成本
#define DEFAULT_CPU_INDEX_TUPLE_COST 0.005 //處理一個索引元組的CPU成本
#define DEFAULT_CPU_OPERATOR_COST 0.0025 //執行一次操作或函式的CPU成本
#define DEFAULT_PARALLEL_TUPLE_COST 0.1 //並行執行,從一個worker傳輸一個元組到另一個worker的成本
#define DEFAULT_PARALLEL_SETUP_COST 1000.0 //構建並行執行環境的成本
#define DEFAULT_EFFECTIVE_CACHE_SIZE 524288 /*先前已有介紹, 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後面10個0,透過設定一個巨大的成本,讓最佳化器自動放棄此路徑
int max_parallel_workers_per_gather = 2;//每次gather使用的worker數
二、原始碼解讀
generate_bitmap_or_paths函式
create_index_paths->generate_bitmap_or_paths函式從條件子句連結串列中尋找OR子句,如找到並且可以處理則生成BitmapOrPath.函式返回生成的連結串列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.
* 從條件子句連結串列中尋找OR子句,如找到並且可以處理則生成BitmapOrPath.
* 函式返回生成的連結串列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是一個附加子句連結串列，
* 為了生成索引條件，可以假定為true，但不能用於搜尋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.
* 使用當前和其他子句作為build_paths_for_OR函式的輸入引數
* 從而不需要從列表中刪除OR子句。
*/
all_clauses = list_concat(list_copy(clauses), other_clauses);//合併到連結串列中
foreach(lc, clauses)//遍歷子句連結串列
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);//約束條件
List *pathlist;//路徑連結串列
Path *bitmapqual;//
ListCell *j;
/* Ignore RestrictInfos that aren't ORs */
if (!restriction_is_or_clause(rinfo))//不是OR子句,處理下一個子句
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.
* 必須能夠將至少一個索引匹配到OR的某個分支，否則無法使用索引。
*/
pathlist = NIL;
foreach(j, ((BoolExpr *) rinfo->orclause)->args)//遍歷OR子句引數
{
Node *orarg = (Node *) lfirst(j);//引數節點
List *indlist;
/* OR arguments should be ANDs or sub-RestrictInfos */
//OR子句的引數必須是AND子句或者是子約束條件
if (and_clause(orarg))//如為AND子句
{
List *andargs = ((BoolExpr *) orarg)->args;//獲取AND子句的引數
indlist = build_paths_for_OR(root, rel,
andargs,
all_clauses);//構建路徑
/* Recurse in case there are sub-ORs */
//遞迴呼叫generate_bitmap_or_paths,並新增到訪問路徑連結串列中
indlist = list_concat(indlist,
generate_bitmap_or_paths(root, rel,
andargs,
all_clauses));
}
else
{
RestrictInfo *rinfo = castNode(RestrictInfo, orarg);//不是AND,則為約束條件
List *orargs;
Assert(!restriction_is_or_clause(rinfo));
orargs = list_make1(rinfo);
indlist = build_paths_for_OR(root, rel,
orargs,
all_clauses);//構建訪問路徑
}
/*
* 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.
* 選擇最有希望的組合，並將其新增到路徑列表中。
*/
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.
* 如果左右兩邊都匹配，那麼將它們轉換為BitmapOrPath，並新增到結果列表中。
*/
if (pathlist != NIL)
{
//建立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.
* 給定OR子句的約束條件子句,構建該Relation所有匹配的索引訪問路徑.
*
* Here we must scan all indexes of the relation, since a bitmap OR tree
* can use multiple indexes.
* BitmapOr可能會使用多個索引,因此需要訪問該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.
* 函式呼叫方提供了2個約束條件子句連結串列,一個是"current",另外一個是"other".
* 這兩個連結串列都可以用於資源匹配索引鍵,但是索引必須使用至少一個存在於"current"中的子句.
* 舉個例子,有下面的條件語句:
* WHERE (x = 42) AND (... OR (y = 52 AND z = 77) OR ....)
* 在考察OR中的x/z子句時,可以使用"x = 42"作為可用的索引條件,但
* 但不應該將子句單獨與x上的任何索引進行匹配，因為這樣的訪問路徑已經在上層生成。
* 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.
* 在處理部分索引時,與索引謂詞匹配的"current"子句同樣可以使用此索引.
*
* '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
* 輸入引數:
* rel-需要生成訪問路徑的Relation
* clauses-"current"子句,節點型別為RestrictInfo
* other_clauses-"other"子句,上層子句已處理
*/
static List *
build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
List *clauses, List *other_clauses)
{
List *result = NIL;//返回結果
List *all_clauses = NIL; /* not computed till needed */
ListCell *lc;//臨時變數
foreach(lc, rel->indexlist)//遍歷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)//索引不支援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.
* 忽略不匹配查詢的部分索引。如predOK標記為T,則可考慮使用此索引.
* 否則，必須測試新增的子句是否足以包含索引謂詞.
* 在這種情況下才可以在當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.)
* 如驗證透過,則將useful_predicate設定為T。
* 這是為了避免predOK索引與OR的某個分支相匹配，這是一個合法但無意義的低效計劃。
* (只需要掃描部分索引就可以產生一個更好的計劃，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.
* 標記與索引匹配的約束條件子句
*/
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)//沒有合適的,繼續下一個索引
continue;
/*
* Add "other" restriction clauses to the clauseset.
*/
match_clauses_to_index(index, other_clauses, &clauseset);//新增到clauseset中
/*
* Construct paths if possible.
*/
indexpaths = build_index_paths(root, rel,
index, &clauseset,
useful_predicate,
ST_BITMAPSCAN,
NULL,
NULL);//構建索引訪問路徑
result = list_concat(result, indexpaths);
}
return result;
}
//------------------------------------------------------ create_bitmap_or_path
/*
* create_bitmap_or_path
* Creates a path node representing a BitmapOr.
* 建立BitmapOr路徑節點
*/
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);//計算成本
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.
* 我們估算或計算選擇率的前提是輸入不重疊，因為存在“x in (list)”這樣的情況。
* 當然，我們在最後調整為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.
* 對於所需的每個tbm_union操作,
* BitmapOr本身的執行時成本估計為100 x cpu_operator_cost。
* 這個估值是否太小，太簡單了?其實，當輸入是點陣圖索引掃描時，tbm_unions已被最佳化。
*/
totalCost = 0.0;//成本
selec = 0.0;//選擇率
foreach(l, path->bitmapquals)//遍歷條件
{
Path *subpath = (Path *) lfirst(l);//路徑
Cost subCost;//成本
Selectivity subselec;
cost_bitmap_tree_node(subpath, &subCost, &subselec);//遍歷路徑獲取成本&選擇率
selec += subselec;//
totalCost += subCost;
if (l != list_head(path->bitmapquals) &&
!IsA(subpath, IndexPath))
totalCost += 100.0 * cpu_operator_cost;//非單個條件而且不是索引訪問路徑,則新增執行期成本
}
path->bitmapselectivity = Min(selec, 1.0);//選擇率
path->path.rows = 0; /* per above, not used */
path->path.startup_cost = totalCost;
path->path.total_cost = totalCost;
}
三、跟蹤分析
測試指令碼如下
select t1.*
from t_dwxx t1
where (dwbh > '10000' and dwbh < '30000')
OR (dwdz between 'DWDZ10000' and 'DWDZ20000');
啟動gdb跟蹤
(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;
檢視輸入引數,clauses是連結串列,只有一個元素(BoolExpr型別,即OR子句);other_clauses為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}
遍歷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))
遍歷OR子句的引數
(gdb)
1292 foreach(j, ((BoolExpr *) rinfo->orclause)->args)
引數的第一個元素,BoolExpr,boolop運算子為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子句的引數
(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)
進入build_paths_for_OR函式
(gdb) step
build_paths_for_OR (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaea90, other_clauses=0x2aaf598) at indxpath.c:1170
1170 List *result = NIL;
遍歷索引,第一個索引是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)
--
與約束條件不匹配((dwbh > '10000' and dwbh < '30000')),繼續下一個索引
1229 if (!clauseset.nonempty && !useful_predicate)
(gdb) p clauseset
$20 = {nonempty = false, indexclauses = {0x0 <repeats 32 times>}}
(gdb) n
1230 continue;
下一個索引是idx_dwxx_predicate_dwmc/idx_dwxx_expr,同樣不匹配,繼續尋找索引,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>}}
構建索引訪問路徑
(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函式
1250 }
(gdb)
generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0) at indxpath.c:1307
1307 indlist = list_concat(indlist,
遞迴進入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;
#直接結束
(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
完成第一輪迴圈
(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}
這是第二個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;
完成第二輪迴圈
(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}
結束迴圈,構建BitmapOrPath
1347 if (pathlist != NIL)
(gdb)
1349 bitmapqual = (Path *) create_bitmap_or_path(root, rel, pathlist);
進入create_bitmap_or_path,呼叫函式cost_bitmap_or_node計算成本
(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
...
計算結果,與執行計劃中的資訊相匹配"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);
完成,DONE!
(gdb) n
1276 foreach(lc, clauses)
(gdb)
1354 return result;
(gdb)
1355 }
四、參考資料
allpaths.c
cost.h
costsize.c
PG Document:Query Planning
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/6906/viewspace-2374845/，如需轉載，請註明出處，否則將追究法律責任。
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