PostgreSQL 原始碼解讀（63）- 查詢語句#48（make_one_rel函式#13-...
本節大體介紹了make_one_rel中的make_rel_from_joinlist->standard_join_search函式的實現邏輯，該函式是PG使用動態規劃演算法構造連線路徑的實現。
一、原始碼解讀
上節已解讀了make_rel_from_joinlist->standard_join_search函式的主實現邏輯,下面重點介紹該函式中的join_search_one_level函式.
/*
* join_search_one_level
* Consider ways to produce join relations containing exactly 'level'
* jointree items. (This is one step of the dynamic-programming method
* embodied in standard_join_search.) Join rel nodes for each feasible
* combination of lower-level rels are created and returned in a list.
* Implementation paths are created for each such joinrel, too.
* 規劃如何生成包含匹配Leve(比如2個關係的連線/3個關係的連線等)連線關係。
* (這是在standard_join_search中體現的動態規劃演算法的一個步驟。)
* 為較低Leve的關係建立新的連線關係亦即訪問路徑,透過連結串列的方式返回(root->join_rel_level)。
*
* level: level of rels we want to make this time
* root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
* level:關係的level,比如是2個關係還是3個關係的連線
*
* The result is returned in root->join_rel_level[level].
* 結果透過root->join_rel_level[level]
*/
void
join_search_one_level(PlannerInfo *root, int level)
{
List **joinrels = root->join_rel_level;
ListCell *r;
int k;
Assert(joinrels[level] == NIL);
/* Set join_cur_level so that new joinrels are added to proper list */
root->join_cur_level = level;//當前的Level
/*
* First, consider left-sided and right-sided plans, in which rels of
* exactly level-1 member relations are joined against initial relations.
* We prefer to join using join clauses, but if we find a rel of level-1
* members that has no join clauses, we will generate Cartesian-product
* joins against all initial rels not already contained in it.
* 首先,規劃left-sided和right-sided的計劃,這些計劃已由初始關係連線為level-1級的Relation.
* PG使用連線條件進行連線,但如果發現level-1成員中沒有連線條件,那麼PG將會
* 為未包含此條件的初始關係生成笛卡爾積.
*/
foreach(r, joinrels[level - 1])//遍歷上一級生成的關係
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);//獲取上一級的RelOptInfo
if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
has_join_restriction(root, old_rel))//存在連線條件
{
/*
* There are join clauses or join order restrictions relevant to
* this rel, so consider joins between this rel and (only) those
* initial rels it is linked to by a clause or restriction.
* 存在與此rel相關的連線條件或連線順序限制，
* 因此僅規劃此rel與透過條件子句或約束條件連結在一起的初始rels.
*
* At level 2 this condition is symmetric, so there is no need to
* look at initial rels before this one in the list; we already
* considered such joins when we were at the earlier rel. (The
* mirror-image joins are handled automatically by make_join_rel.)
* In later passes (level > 2), we join rels of the previous level
* to each initial rel they don't already include but have a join
* clause or restriction with.
* leve=2時，這個條件是對稱的，所以不需要在關注連結串列中此rel前的rels;
* 在處理在此rel前的rels時,已處理這樣的連線.(make_join_rel函式自動處理映象連線)。
* level>2時，PG將上一級別生成的rels逐一與尚未處理的初始rel(存在連線條件或約束條件)進行連線.
*
*/
ListCell *other_rels;
if (level == 2) /* consider remaining initial rels */
other_rels = lnext(r);//level = 2,只需關注此rel之後的rel
else /* consider all initial rels */
other_rels = list_head(joinrels[1]);//level > 2,從第1級開始嘗試
make_rels_by_clause_joins(root,
old_rel,
other_rels);//建立連線
}
else//不存在連線條件
{
/*
* Oops, we have a relation that is not joined to any other
* relation, either directly or by join-order restrictions.
* Cartesian product time.
* 有一個relation與其他relation沒有連線條件(直接或透過join-order約束)
* 笛卡爾時間到了!
*
* We consider a cartesian product with each not-already-included
* initial rel, whether it has other join clauses or not. At
* level 2, if there are two or more clauseless initial rels, we
* will redundantly consider joining them in both directions; but
* such cases aren't common enough to justify adding complexity to
* avoid the duplicated effort.
* 考察每一個尚未處理的初始rel(無論其是否有約束條件).
* 在level 2,如存在2個或以上的無條件初始rels,PG可能會出現重複處理的情況.
*/
make_rels_by_clauseless_joins(root,
old_rel,
list_head(joinrels[1]));//建立無條件連線
}
}
/*
* Now, consider "bushy plans" in which relations of k initial rels are
* joined to relations of level-k initial rels, for 2 <= k <= level-2.
* 現在考察"稠密計劃",其中k level的rels與level - k的rel想連線.其中:2 <= k <= level-2
*
* We only consider bushy-plan joins for pairs of rels where there is a
* suitable join clause (or join order restriction), in order to avoid
* unreasonable growth of planning time.
* 這裡只考慮存在連線條件(或者join-order限制)的關係對,以避免計劃時間的大幅增加
*/
for (k = 2;; k++)
{
int other_level = level - k;
/*
* Since make_join_rel(x, y) handles both x,y and y,x cases, we only
* need to go as far as the halfway point.
*/
if (k > other_level)
break;
foreach(r, joinrels[k])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
ListCell *r2;
/*
* We can ignore relations without join clauses here, unless they
* participate in join-order restrictions --- then we might have
* to force a bushy join plan.
*/
if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
!has_join_restriction(root, old_rel))
continue;
if (k == other_level)
other_rels = lnext(r); /*同一層次,只考慮餘下的rel,only consider remaining rels */
else
other_rels = list_head(joinrels[other_level]);//不同層次,嘗試所有的
for_each_cell(r2, other_rels)
{
RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
if (!bms_overlap(old_rel->relids, new_rel->relids))//relids不存在包含關係
{
/*
* OK, we can build a rel of the right level from this
* pair of rels. Do so if there is at least one relevant
* join clause or join order restriction.
*/
if (have_relevant_joinclause(root, old_rel, new_rel) ||
have_join_order_restriction(root, old_rel, new_rel))//存在連線條件或者join-order約束
{
(void) make_join_rel(root, old_rel, new_rel);//建立連線
}
}
}
}
}
/*----------
* Last-ditch effort: if we failed to find any usable joins so far, force
* a set of cartesian-product joins to be generated. This handles the
* special case where all the available rels have join clauses but we
* cannot use any of those clauses yet. This can only happen when we are
* considering a join sub-problem (a sub-joinlist) and all the rels in the
* sub-problem have only join clauses with rels outside the sub-problem.
* An example is
*
* SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
* WHERE a.w = c.x and b.y = d.z;
*
* If the "a INNER JOIN b" sub-problem does not get flattened into the
* upper level, we must be willing to make a cartesian join of a and b;
* but the code above will not have done so, because it thought that both
* a and b have joinclauses. We consider only left-sided and right-sided
* cartesian joins in this case (no bushy).
*----------
*/
if (joinrels[level] == NIL)
{
/*
* This loop is just like the first one, except we always call
* make_rels_by_clauseless_joins().
*/
foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
make_rels_by_clauseless_joins(root,
old_rel,
list_head(joinrels[1]));
}
/*----------
* When special joins are involved, there may be no legal way
* to make an N-way join for some values of N. For example consider
*
* SELECT ... FROM t1 WHERE
* x IN (SELECT ... FROM t2,t3 WHERE ...) AND
* y IN (SELECT ... FROM t4,t5 WHERE ...)
*
* We will flatten this query to a 5-way join problem, but there are
* no 4-way joins that join_is_legal() will consider legal. We have
* to accept failure at level 4 and go on to discover a workable
* bushy plan at level 5.
*
* However, if there are no special joins and no lateral references
* then join_is_legal() should never fail, and so the following sanity
* check is useful.
*----------
*/
if (joinrels[level] == NIL &&
root->join_info_list == NIL &&
!root->hasLateralRTEs)
elog(ERROR, "failed to build any %d-way joins", level);
}
}
//------------------------------------------------------------------- has_join_restriction
/*
* has_join_restriction
* Detect whether the specified relation has join-order restrictions,
* due to being inside an outer join or an IN (sub-SELECT),
* or participating in any LATERAL references or multi-rel PHVs.
* 判斷傳入的relation是否含有join-order限制條件.存在於外連線/IN(sub-SELECT)子查詢/LATERAL依賴/多關係PHVs
*
* Essentially, this tests whether have_join_order_restriction() could
* succeed with this rel and some other one. It's OK if we sometimes
* say "true" incorrectly. (Therefore, we don't bother with the relatively
* expensive has_legal_joinclause test.)
*/
static bool
has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
{
ListCell *l;
if (rel->lateral_relids != NULL || rel->lateral_referencers != NULL)
return true;//存在lateral
foreach(l, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
if (bms_is_subset(rel->relids, phinfo->ph_eval_at) &&
!bms_equal(rel->relids, phinfo->ph_eval_at))
return true;//PHVs
}
foreach(l, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms preserve their ordering */
if (sjinfo->jointype == JOIN_FULL)
continue;//不考慮全外連線
/* ignore if SJ is already contained in rel */
if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
bms_is_subset(sjinfo->min_righthand, rel->relids))
continue;//SJ在rel中,不考慮
/* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
bms_overlap(sjinfo->min_righthand, rel->relids))
return true;
}
return false;
}
//------------------------------------------------------------------- make_rels_by_clause_joins
/*
* make_rels_by_clause_joins
* Build joins between the given relation 'old_rel' and other relations
* that participate in join clauses that 'old_rel' also participates in
* (or participate in join-order restrictions with it).
* The join rels are returned in root->join_rel_level[join_cur_level].
* 建立old_rel和其他rel的連線(兩者存在連線條件)
*
* Note: at levels above 2 we will generate the same joined relation in
* multiple ways --- for example (a join b) join c is the same RelOptInfo as
* (b join c) join a, though the second case will add a different set of Paths
* to it. This is the reason for using the join_rel_level mechanism, which
* automatically ensures that each new joinrel is only added to the list once.
* 注意:在level > 2時,PG會透過多種方式生成同樣的連線rel(joined relation).
* 比如:(a join b) join c與(b join c) join a最終結果是一樣的RelOptInfo,雖然第
* 2種方法會新增一些不同的訪問路徑集合在其中.
* 這其實是使用join_rel_level的原因,確保每個新joinrel只加入到合適的連結串列中
*
* 'old_rel' is the relation entry for the relation to be joined
* 'other_rels': the first cell in a linked list containing the other
* rels to be considered for joining
* old-rel:需要連線的rel
* other-rel:候選關係連結串列中的的第一個cell
*
* Currently, this is only used with initial rels in other_rels, but it
* will work for joining to joinrels too.
* 看起來似乎只對other_rels中的初始rels有用,但其實對於連線生成的joinrels同樣會生效.
*/
static void
make_rels_by_clause_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels)
{
ListCell *l;
for_each_cell(l, other_rels)//遍歷連結串列
{
RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);//獲取其中的RelOptInfo
if (!bms_overlap(old_rel->relids, other_rel->relids) &&
(have_relevant_joinclause(root, old_rel, other_rel) ||
have_join_order_restriction(root, old_rel, other_rel)))//reldis不同而且存在連線關係&連線順序約束
{
(void) make_join_rel(root, old_rel, other_rel);//建立連線
}
}
}
//---------------------------------------------------- have_relevant_joinclause
/*
* have_relevant_joinclause
* Detect whether there is a joinclause that involves
* the two given relations.
* 給定兩個relations,檢查兩者是否存在連線條件
*
* Note: the joinclause does not have to be evaluable with only these two
* relations. This is intentional. For example consider
* SELECT * FROM a, b, c WHERE a.x = (b.y + c.z)
* If a is much larger than the other tables, it may be worthwhile to
* cross-join b and c and then use an inner indexscan on a.x. Therefore
* we should consider this joinclause as reason to join b to c, even though
* it can't be applied at that join step.
* 注意:連線條件不一定是等值連線,
* 比如:SELECT * FROM a, b, c WHERE a.x = (b.y + c.z),只要a.x大於b.y + c.z即可
*/
bool
have_relevant_joinclause(PlannerInfo *root,
RelOptInfo *rel1, RelOptInfo *rel2)
{
bool result = false;
List *joininfo;
Relids other_relids;
ListCell *l;
/*
* We could scan either relation's joininfo list; may as well use the
* shorter one.
* 獲取relation中joininfo連結串列較少的那個
*/
if (list_length(rel1->joininfo) <= list_length(rel2->joininfo))
{
joininfo = rel1->joininfo;
other_relids = rel2->relids;
}
else
{
joininfo = rel2->joininfo;
other_relids = rel1->relids;
}
foreach(l, joininfo)//遍歷
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
if (bms_overlap(other_relids, rinfo->required_relids))//存在交集
{
result = true;//存在連線條件
break;
}
}
/*
* We also need to check the EquivalenceClass data structure, which might
* contain relationships not emitted into the joininfo lists.
* 檢查等價類
*/
if (!result && rel1->has_eclass_joins && rel2->has_eclass_joins)
result = have_relevant_eclass_joinclause(root, rel1, rel2);//存在等價類連線條件
return result;
}
//---------------------------------------------------- have_join_order_restriction
/*
* have_join_order_restriction
* Detect whether the two relations should be joined to satisfy
* a join-order restriction arising from special or lateral joins.
* 檢查兩個relations是否需要連線以滿足join-order限制(由於special/lateral連線引起)
*
* In practice this is always used with have_relevant_joinclause(), and so
* could be merged with that function, but it seems clearer to separate the
* two concerns. We need this test because there are degenerate cases where
* a clauseless join must be performed to satisfy join-order restrictions.
* Also, if one rel has a lateral reference to the other, or both are needed
* to compute some PHV, we should consider joining them even if the join would
* be clauseless.
* 在實踐中，這通常與have_relevance _join子()一起使用，因此可以與該函式合併，
* 但分離這兩個關注點似乎更為清晰。在一些退化的情況下需要這個測試，
* 必須執行無語法連線以滿足連線順序限制。
* 另外，如果一個rel與另一個rel有一個lateral引用，
* 或者兩者都需要計算一些PHV，那麼我們應該考慮加入它們，即使連線是無連線條件的。
*
* Note: this is only a problem if one side of a degenerate outer join
* contains multiple rels, or a clauseless join is required within an
* IN/EXISTS RHS; else we will find a join path via the "last ditch" case in
* join_search_one_level(). We could dispense with this test if we were
* willing to try bushy plans in the "last ditch" case, but that seems much
* less efficient.
* 注意:只有當簡併外部連線的一側包含多個rels時，
* 或者在IN/EXISTS RHS中需要一個無修飾的連線時，才會出現這個問題;
* 否則，將透過join_search_one_level()中的“last ditch”
* 找到連線路徑。如果願意在“稠密計劃”的情況下進行大量的嘗試，
* 那麼可以省去這個測試，但這似乎效率要低得多。
*/
bool
have_join_order_restriction(PlannerInfo *root,
RelOptInfo *rel1, RelOptInfo *rel2)
{
bool result = false;
ListCell *l;
/*
* If either side has a direct lateral reference to the other, attempt the
* join regardless of outer-join considerations.
*/
if (bms_overlap(rel1->relids, rel2->direct_lateral_relids) ||
bms_overlap(rel2->relids, rel1->direct_lateral_relids))
return true;//relids與lateral relids存在交集,返回T
/*
* Likewise, if both rels are needed to compute some PlaceHolderVar,
* attempt the join regardless of outer-join considerations. (This is not
* very desirable, because a PHV with a large eval_at set will cause a lot
* of probably-useless joins to be considered, but failing to do this can
* cause us to fail to construct a plan at all.)
*/
foreach(l, root->placeholder_list)//遍歷PHV
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
if (bms_is_subset(rel1->relids, phinfo->ph_eval_at) &&
bms_is_subset(rel2->relids, phinfo->ph_eval_at))
return true;
}
/*
* It's possible that the rels correspond to the left and right sides of a
* degenerate outer join, that is, one with no joinclause mentioning the
* non-nullable side; in which case we should force the join to occur.
*
* Also, the two rels could represent a clauseless join that has to be
* completed to build up the LHS or RHS of an outer join.
*/
foreach(l, root->join_info_list)//遍歷連線連結串列
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms handle them */
if (sjinfo->jointype == JOIN_FULL)
continue;
/* Can we perform the SJ with these rels? */
if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
bms_is_subset(sjinfo->min_righthand, rel2->relids))
{
result = true;
break;
}
if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
bms_is_subset(sjinfo->min_righthand, rel1->relids))
{
result = true;
break;
}
/*
* Might we need to join these rels to complete the RHS? We have to
* use "overlap" tests since either rel might include a lower SJ that
* has been proven to commute with this one.
*/
if (bms_overlap(sjinfo->min_righthand, rel1->relids) &&
bms_overlap(sjinfo->min_righthand, rel2->relids))
{
result = true;
break;
}
/* Likewise for the LHS. */
if (bms_overlap(sjinfo->min_lefthand, rel1->relids) &&
bms_overlap(sjinfo->min_lefthand, rel2->relids))
{
result = true;
break;
}
}
/*
* We do not force the join to occur if either input rel can legally be
* joined to anything else using joinclauses. This essentially means that
* clauseless bushy joins are put off as long as possible. The reason is
* that when there is a join order restriction high up in the join tree
* (that is, with many rels inside the LHS or RHS), we would otherwise
* expend lots of effort considering very stupid join combinations within
* its LHS or RHS.
*/
if (result)
{
if (has_legal_joinclause(root, rel1) ||
has_legal_joinclause(root, rel2))
result = false;
}
return result;
}
二、跟蹤分析
建立測試資料表並生成測試資料:
drop table if exists a;
drop table if exists b;
drop table if exists c;
drop table if exists d;
drop table if exists e;
drop table if exists f;
create table a(c1 int,c2 varchar(20));
create table b(c1 int,c2 varchar(20));
create table c(c1 int,c2 varchar(20));
create table d(c1 int,c2 varchar(20));
create table e(c1 int,c2 varchar(20));
create table f(c1 int,c2 varchar(20));
insert into a select generate_series(1,100),'TEST'||generate_series(1,100);
insert into b select generate_series(1,1000),'TEST'||generate_series(1,1000);
insert into c select generate_series(1,10000),'TEST'||generate_series(1,10000);
insert into d select generate_series(1,200),'TEST'||generate_series(1,200);
insert into e select generate_series(1,4000),'TEST'||generate_series(1,4000);
insert into f select generate_series(1,100000),'TEST'||generate_series(1,100000);
測試指令碼:
testdb=# explain verbose select a.*,b.c1,c.c2,d.c2,e.c1,f.c2
from a inner join b on a.c1=b.c1,c,d,e inner join f on e.c1 = f.c1 and e.c1 < 100
where a.c1=f.c1 and b.c1=c.c1 and c.c1 = d.c1 and d.c1 = e.c1;
QUERY PLAN
----------------------------------------------------------------------------------------------------------
Nested Loop (cost=101.17..2218.24 rows=2 width=42)
Output: a.c1, a.c2, b.c1, c.c2, d.c2, e.c1, f.c2
Join Filter: (a.c1 = b.c1)
-> Hash Join (cost=3.25..196.75 rows=100 width=22)
Output: a.c1, a.c2, c.c2, c.c1
Hash Cond: (c.c1 = a.c1)
-> Seq Scan on public.c (cost=0.00..155.00 rows=10000 width=12)
Output: c.c1, c.c2
-> Hash (cost=2.00..2.00 rows=100 width=10)
Output: a.c1, a.c2
-> Seq Scan on public.a (cost=0.00..2.00 rows=100 width=10)
Output: a.c1, a.c2
-> Materialize (cost=97.92..2014.00 rows=5 width=32)
Output: b.c1, d.c2, d.c1, e.c1, f.c2, f.c1
-> Hash Join (cost=97.92..2013.97 rows=5 width=32)
Output: b.c1, d.c2, d.c1, e.c1, f.c2, f.c1
Hash Cond: (f.c1 = b.c1)
-> Seq Scan on public.f (cost=0.00..1541.00 rows=100000 width=13)
Output: f.c1, f.c2
-> Hash (cost=97.86..97.86 rows=5 width=19)
Output: b.c1, d.c2, d.c1, e.c1
-> Hash Join (cost=78.10..97.86 rows=5 width=19)
Output: b.c1, d.c2, d.c1, e.c1
Hash Cond: (b.c1 = e.c1)
-> Seq Scan on public.b (cost=0.00..16.00 rows=1000 width=4)
Output: b.c1, b.c2
-> Hash (cost=78.04..78.04 rows=5 width=15)
Output: d.c2, d.c1, e.c1
-> Hash Join (cost=73.24..78.04 rows=5 width=15)
Output: d.c2, d.c1, e.c1
Hash Cond: (d.c1 = e.c1)
-> Seq Scan on public.d (cost=0.00..4.00 rows=200 width=11)
Output: d.c1, d.c2
-> Hash (cost=72.00..72.00 rows=99 width=4)
Output: e.c1
-> Seq Scan on public.e (cost=0.00..72.00 rows=99 width=4)
Output: e.c1
Filter: (e.c1 < 100)
(38 rows)
測試SQL語句的連線關係:a-b,a-f,b-c,c-d,d-e,e-f
注:根據先前章節的知識,該SQL語句存在等價類{a.c1 b.c1 c.c1 d.c1 e.c1 f.c1}
啟動gdb跟蹤
(gdb) b join_search_one_level
Breakpoint 1 at 0x755667: file joinrels.c, line 67.
(gdb) c
Continuing.
Breakpoint 1, join_search_one_level (root=0x3006e28, level=2) at joinrels.c:67
67 List **joinrels = root->join_rel_level;
檢視最佳化器資訊(root)
(gdb) p *root
$13 = {type = T_PlannerInfo, parse = 0x2fa3410, glob = 0x3008578, query_level = 1, parent_root = 0x0, plan_params = 0x0,
outer_params = 0x0, simple_rel_array = 0x2f510e8, simple_rel_array_size = 9, simple_rte_array = 0x2f51178,
all_baserels = 0x2f53dd8, nullable_baserels = 0x0, join_rel_list = 0x2fcb5c8, join_rel_hash = 0x0,
join_rel_level = 0x2fcafe8, join_cur_level = 2, init_plans = 0x0, cte_plan_ids = 0x0, multiexpr_params = 0x0,
eq_classes = 0x2f52cb8, canon_pathkeys = 0x2fcb718, left_join_clauses = 0x0, right_join_clauses = 0x0,
full_join_clauses = 0x0, join_info_list = 0x0, append_rel_list = 0x0, rowMarks = 0x0, placeholder_list = 0x0,
fkey_list = 0x0, query_pathkeys = 0x0, group_pathkeys = 0x0, window_pathkeys = 0x0, distinct_pathkeys = 0x0,
sort_pathkeys = 0x0, part_schemes = 0x0, initial_rels = 0x2fcaf18, upper_rels = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
upper_targets = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, processed_tlist = 0x2f4f718, grouping_map = 0x0, minmax_aggs = 0x0,
planner_cxt = 0x2e87040, total_table_pages = 627, tuple_fraction = 0, limit_tuples = -1, qual_security_level = 0,
inhTargetKind = INHKIND_NONE, hasJoinRTEs = true, hasLateralRTEs = false, hasDeletedRTEs = false, hasHavingQual = false,
hasPseudoConstantQuals = false, hasRecursion = false, wt_param_id = -1, non_recursive_path = 0x0, curOuterRels = 0x0,
curOuterParams = 0x0, join_search_private = 0x0, partColsUpdated = false}
root->simple_rel_array_size=9,陣列中有9個元素,從1-8(下標為0的元素無用)分別是1->RTE_RELATION/16775,2->RTE_RELATION/16778,3->RTE_JOIN,4->RTE_RELATION/16781,5->RTE_RELATION/16784,6->RTE_RELATION/16787,7->RTE_RELATION/16790,8->RTE_JOIN
oid | relname
-------+---------
16775 | a -->1
16778 | b -->2
16781 | c -->4
16784 | d -->5
16787 | e -->6
16790 | f -->7
(6 rows)
進入join_search_one_level函式,level=2,開始迴圈遍歷joinrels
(gdb) n
74 root->join_cur_level = level;
(gdb)
83 foreach(r, joinrels[level - 1])
(gdb) n
85 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
(gdb)
87 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
(gdb)
105 if (level == 2) /* consider remaining initial rels */
(gdb)
106 other_rels = lnext(r);
(gdb)
110 make_rels_by_clause_joins(root,
[level=2]進入make_rels_by_clause_joins函式
(gdb) step
make_rels_by_clause_joins (root=0x3006e28, old_rel=0x3008258, other_rels=0x2fcaf48) at joinrels.c:280
280 for_each_cell(l, other_rels)
[level=2]由於存在等價類{a.c1 b.c1 c.c1 d.c1 e.c1 f.c1},因此這一步驟會兩兩連線構造新的關係,ab,ac,ad,ae,af,bc,bd,...
(gdb) n
282 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
(gdb)
284 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
(gdb)
285 (have_relevant_joinclause(root, old_rel, other_rel) ||
(gdb)
284 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
(gdb)
288 (void) make_join_rel(root, old_rel, other_rel);
(gdb) n
280 for_each_cell(l, other_rels)
[level=2]呼叫make_join_rel函式後,檢視root->join_rel_level[2],relids=6=2+4,這是1號(關係a)和2號(關係b)RTE的連線.
(gdb) p *root->join_rel_level[2]
$6 = {type = T_List, length = 1, head = 0x2fcb5f8, tail = 0x2fcb5f8}
(gdb) p *(Node *)root->join_rel_level[2]->head->data.ptr_value
$7 = {type = T_RelOptInfo}
(gdb) p *(RelOptInfo *)root->join_rel_level[2]->head->data.ptr_value
$8 = {type = T_RelOptInfo, reloptkind = RELOPT_JOINREL, relids = 0x2fcb050, rows = 100, consider_startup = false,
consider_param_startup = false, consider_parallel = true, reltarget = 0x2fcb068, pathlist = 0x2fcba08, ppilist = 0x0,
partial_pathlist = 0x0, cheapest_startup_path = 0x0, cheapest_total_path = 0x0, cheapest_unique_path = 0x0,
cheapest_parameterized_paths = 0x0, direct_lateral_relids = 0x0, lateral_relids = 0x0, relid = 0, reltablespace = 0,
rtekind = RTE_JOIN, min_attr = 0, max_attr = 0, attr_needed = 0x0, attr_widths = 0x0, lateral_vars = 0x0,
lateral_referencers = 0x0, indexlist = 0x0, statlist = 0x0, pages = 0, tuples = 0, allvisfrac = 0, subroot = 0x0,
subplan_params = 0x0, rel_parallel_workers = -1, serverid = 0, userid = 0, useridiscurrent = false, fdwroutine = 0x0,
fdw_private = 0x0, unique_for_rels = 0x0, non_unique_for_rels = 0x0, baserestrictinfo = 0x0, baserestrictcost = {
startup = 0, per_tuple = 0}, baserestrict_min_security = 4294967295, joininfo = 0x0, has_eclass_joins = true,
top_parent_relids = 0x0, part_scheme = 0x0, nparts = 0, boundinfo = 0x0, partition_qual = 0x0, part_rels = 0x0,
partexprs = 0x0, nullable_partexprs = 0x0, partitioned_child_rels = 0x0}
(gdb) set $tmp=(RelOptInfo *)root->join_rel_level[2]->head->data.ptr_value
(gdb) p *$tmp->relids->words
$10 = 6
[level=2]繼續迴圈,下幾組分別是ac,ad,ae,af
(gdb) p *$tmp->relids->words
$12 = 18/34/66/130
[level=2]完成對關係a的兩兩連線
(gdb) n
291 }
(gdb)
join_search_one_level (root=0x3006e28, level=2) at joinrels.c:89
89 {
(gdb) n
83 foreach(r, joinrels[level - 1])
[level=2]類似的,處理b/c/d/e/f,兩兩形成連線,一共有15種組合(6!/(2!*(6-2)!))
(gdb)
83 foreach(r, joinrels[level - 1])
(gdb)
142 for (k = 2;; k++)
(gdb) p *root->join_rel_level[2]
$44 = {type = T_List, length = 15, head = 0x2fcb5f8, tail = 0x2fd7f78}
[level=2]完成level=2的呼叫,level2的relids組合有1&2,1&4,1&5,1&6,1&7,2&4,2&5,2&6,2&7,4&5,4&6,4&7,5&6,5&7,6&7
(gdb)
standard_join_search (root=0x3006e28, levels_needed=6, initial_rels=0x2fcaf18) at allpaths.c:2757
2757 foreach(lc, root->join_rel_level[lev])
開始level=3的呼叫
(gdb) c
Continuing.
Breakpoint 1, join_search_one_level (root=0x3006e28, level=3) at joinrels.c:67
67 List **joinrels = root->join_rel_level;
[level=3]遍歷level=2的RelOptInfo(兩兩連線形成的新關係)
(gdb)
83 foreach(r, joinrels[level - 1])
[level=3]與level=2不同,選擇初始的RelOptInfo進行連線,而不是同級的rels
...
(gdb)
108 other_rels = list_head(joinrels[1]);
[level=3]完成第一輪的迴圈,root->join_rel_level[3]連結串列中有4個Node(RelOptInfo),其relids分別是22/38/70/134,即1&2&4,1&2&5,1&2&6,1&2&7
(gdb) p *((RelOptInfo *)root->join_rel_level[3]->head->data.ptr_value)->relids->words
$55 = 22
(gdb) p *((RelOptInfo *)root->join_rel_level[3]->head->next->data.ptr_value)->relids->words
$56 = 38
(gdb) p *((RelOptInfo *)root->join_rel_level[3]->head->next->next->data.ptr_value)->relids->words
$57 = 70
(gdb) p *((RelOptInfo *)root->join_rel_level[3]->head->next->next->next->data.ptr_value)->relids->words
$58 = 134
[level=3]完成所有迴圈後的root->join_rel_level[3],構成連線的relids組合,一共20個(請參照數學組合的計算),包括1&2&4,1&2&5,1&2&6,1&2&7,1&4&5,1&4&6,1&4&7,...
...
(gdb) p *root->join_rel_level[3]
$68 = {type = T_List, length = 20, head = 0x2fd90d8, tail = 0x2f7f248}
[level=3]嘗試bushy plans,達不到要求,退出迴圈
142 for (k = 2;; k++)
(gdb)
144 int other_level = level - k;
(gdb)
150 if (k > other_level)
150 if (k > other_level)
(gdb) n
151 break;
[level=3]完成level=3的呼叫,開始level 4呼叫
(gdb)
standard_join_search (root=0x3006e28, levels_needed=6, initial_rels=0x2fcaf18) at allpaths.c:2757
2757 foreach(lc, root->join_rel_level[lev])
(gdb) c
Continuing.
Breakpoint 1, join_search_one_level (root=0x3006e28, level=4) at joinrels.c:67
67 List **joinrels = root->join_rel_level;
[level=4]完成第一輪迴圈呼叫,檢視root->join_rel_level[4],relids分別是54/86/150,即1&2&4&5,1&2&4&6,1&2&4&7
...
89 {
(gdb)
83 foreach(r, joinrels[level - 1])
(gdb) p *root->join_rel_level[4]
$69 = {type = T_List, length = 3, head = 0x2f838e0, tail = 0x30654d8}
(gdb) p *((RelOptInfo *)root->join_rel_level[4]->head->data.ptr_value)->relids->words
$70 = 54
(gdb) p *((RelOptInfo *)root->join_rel_level[4]->head->next->data.ptr_value)->relids->words
$71 = 86
(gdb) p *((RelOptInfo *)root->join_rel_level[4]->head->next->next->data.ptr_value)->relids->words
$72 = 150
[level=4]所有迴圈後的root->join_rel_level[4],構成連線的relids組合,一共15個
(gdb) b joinrels.c:142
Breakpoint 2 at 0x75576a: file joinrels.c, line 142.
(gdb) c
Continuing.
Breakpoint 2, join_search_one_level (root=0x3006e28, level=4) at joinrels.c:142
142 for (k = 2;; k++)
(gdb) p *root->join_rel_level[4]
$73 = {type = T_List, length = 15, head = 0x2f838e0, tail = 0x307bd78}
[level=4]嘗試bushy plans
...
(gdb) p k
$74 = 2
(gdb) p other_level
$75 = 2
[level=4]遍歷k級關係,k=other_level,同一層次的rel,兩兩組合,即1&2,3&4等嘗試兩兩配對連線
(gdb) n
153 foreach(r, joinrels[k])
...
(gdb)
168 if (k == other_level)
[level=4]如relids=6和relids=48的兩個關係
177 if (!bms_overlap(old_rel->relids, new_rel->relids))
(gdb)
184 if (have_relevant_joinclause(root, old_rel, new_rel) ||
(gdb) p *old_rel->relids->words
$78 = 6
(gdb) p *new_rel->relids->words
$79 = 48
[level=4]構造新的關係,但該關係無法透過合法連線形成或者已存在,因此沒有對root->join_rel_level[4]有所影響(呼叫前後均為15個Node)
(gdb) n
187 (void) make_join_rel(root, old_rel, new_rel);
(gdb)
173 for_each_cell(r2, other_rels)
(gdb) p *root->join_rel_level[4]
$80 = {type = T_List, length = 15, head = 0x2f838e0, tail = 0x307bd78}
[level=4]完成bushy plans,root->join_rel_level[4]元素個數沒有變化
(gdb) c
Continuing.
Breakpoint 3, join_search_one_level (root=0x3006e28, level=4) at joinrels.c:213
213 if (joinrels[level] == NIL)
(gdb) p *root->join_rel_level[4]
$82 = {type = T_List, length = 15, head = 0x2f838e0, tail = 0x307bd78}
[level=5]進入level=5呼叫
(gdb) c
Continuing.
Breakpoint 1, join_search_one_level (root=0x3006e28, level=5) at joinrels.c:67
67 List **joinrels = root->join_rel_level;
[level=5]完成第一輪迴圈呼叫,檢視root->join_rel_level[5],relids分別是118/182,即1&2&4&5&6,1&2&4&6&7
(gdb) p *root->join_rel_level[5]
$83 = {type = T_List, length = 2, head = 0x30931d0, tail = 0x3093dc8}
(gdb) p *((RelOptInfo *)root->join_rel_level[5]->head->data.ptr_value)->relids->words
$85 = 118
(gdb) p *((RelOptInfo *)root->join_rel_level[5]->head->next->data.ptr_value)->relids->words
$86 = 182
[level=5]所有迴圈後的root->join_rel_level[5],構成連線的relids組合,一共6個
(gdb) p *root->join_rel_level[5]
$87 = {type = T_List, length = 6, head = 0x30931d0, tail = 0x309d188}
[level=5]嘗試bushy plans,即2個rels連線生成的關係 join 3個rels連線生成的關係
完成呼叫
(gdb) c
Continuing.
Breakpoint 3, join_search_one_level (root=0x3006e28, level=5) at joinrels.c:213
213 if (joinrels[level] == NIL)
(gdb) p *root->join_rel_level[5]
$91 = {type = T_List, length = 6, head = 0x30931d0, tail = 0x309d188}
[level=6]進入level=6呼叫
(gdb) c
Continuing.
Breakpoint 1, join_search_one_level (root=0x3006e28, level=6) at joinrels.c:67
67 List **joinrels = root->join_rel_level;
[level=6]與level=1的rels連線後,形成1個新的關係
(gdb) c
Continuing.
Breakpoint 2, join_search_one_level (root=0x3006e28, level=6) at joinrels.c:142
142 for (k = 2;; k++)
(gdb) p *root->join_rel_level[6]
$92 = {type = T_List, length = 1, head = 0x3104cf8, tail = 0x3104cf8}
[level=6]嘗試bushy plans,即2個rels連線生成的關係 join 4個rels連線生成的關係 & 3 join 3
完成呼叫,生成level=6的結果連結串列
(gdb) c
Continuing.
Breakpoint 3, join_search_one_level (root=0x3006e28, level=6) at joinrels.c:213
213 if (joinrels[level] == NIL)
(gdb) p *root->join_rel_level[6]
$93 = {type = T_List, length = 1, head = 0x3104cf8, tail = 0x3104cf8}
(gdb) p *(RelOptInfo *)root->join_rel_level[6]->head->data.ptr_value
$94 = {type = T_RelOptInfo, reloptkind = RELOPT_JOINREL, relids = 0x3099a80, rows = 2, consider_startup = false,
consider_param_startup = false, consider_parallel = true, reltarget = 0x3104a08, pathlist = 0x3104ec0, ppilist = 0x0,
partial_pathlist = 0x0, cheapest_startup_path = 0x0, cheapest_total_path = 0x0, cheapest_unique_path = 0x0,
cheapest_parameterized_paths = 0x0, direct_lateral_relids = 0x0, lateral_relids = 0x0, relid = 0, reltablespace = 0,
rtekind = RTE_JOIN, min_attr = 0, max_attr = 0, attr_needed = 0x0, attr_widths = 0x0, lateral_vars = 0x0,
lateral_referencers = 0x0, indexlist = 0x0, statlist = 0x0, pages = 0, tuples = 0, allvisfrac = 0, subroot = 0x0,
subplan_params = 0x0, rel_parallel_workers = -1, serverid = 0, userid = 0, useridiscurrent = false, fdwroutine = 0x0,
fdw_private = 0x0, unique_for_rels = 0x0, non_unique_for_rels = 0x0, baserestrictinfo = 0x0, baserestrictcost = {
startup = 0, per_tuple = 0}, baserestrict_min_security = 4294967295, joininfo = 0x0, has_eclass_joins = false,
top_parent_relids = 0x0, part_scheme = 0x0, nparts = 0, boundinfo = 0x0, partit
[level=6]檢視訪問路徑
(gdb) set $roi=(RelOptInfo *)root->join_rel_level[6]->head->data.ptr_value
(gdb) p *$roi->pathlist
$97 = {type = T_List, length = 1, head = 0x3104ea0, tail = 0x3104ea0}
(gdb) p *(Node *)$roi->pathlist->head->data.ptr_value
$98 = {type = T_NestPath}
(gdb) p *(NestPath *)$roi->pathlist->head->data.ptr_value
$99 = {path = {type = T_NestPath, pathtype = T_NestLoop, parent = 0x31047f8, pathtarget = 0x3104a08, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 2, startup_cost = 101.1725,
total_cost = 2218.2350000000001, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = false,
outerjoinpath = 0x2fccd80, innerjoinpath = 0x3107820, joinrestrictinfo = 0x3107ae0}
該path的innerjoinpath(構造該連線inner關係的path)和outerjoinpath(構造該連線outer關係的path)
(gdb) p *$np->innerjoinpath
$109 = {type = T_MaterialPath, pathtype = T_Material, parent = 0x3077c70, pathtarget = 0x3077e80, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 5, startup_cost = 97.922499999999999,
total_cost = 2013.9974999999999, pathkeys = 0x0}
(gdb) p *$np->outerjoinpath
$110 = {type = T_HashPath, pathtype = T_HashJoin, parent = 0x2f54050, pathtarget = 0x2fcbf88, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100, startup_cost = 3.25, total_cost = 196.75,
pathkeys = 0x0}
DONE!
(gdb) c
Continuing.
三、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-2374837/，如需轉載，請註明出處，否則將追究法律責任。
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