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這篇文章主要介紹“PostgreSQL中使用動態規劃算法構造連接路徑的實現函數是哪個”，在日常操作中，相信很多人在PostgreSQL中使用動態規劃算法構造連接路徑的實現函數是哪個問題上存在疑惑，小編查閱了各式資料，整理出簡單好用的操作方法，希望對大家解答”PostgreSQL中使用動態規劃算法構造連接路徑的實現函數是哪個”的疑惑有所幫助！接下來，請跟著小編一起來學習吧！
上節已解讀了make_rel_from_joinlist->standard_join_search函數的主實現邏輯,下面重點介紹該函數中的join_search_one_level函數.
/*
* 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個關系的連接/3個關系的連接等)連接關系。
* (這是在standard_join_search中體現的動態規劃算法的一個步驟。)
* 為較低Leve的關系創建新的連接關系亦即訪問路徑,通過鏈表的方式返回(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:關系的level,比如是2個關系還是3個關系的連接
*
* The result is returned in root->join_rel_level[level].
* 結果通過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系連接為level-1級的Relation.
* PG使用連接條件進行連接,但如果發現level-1成員中沒有連接條件,那么PG將會
* 為未包含此條件的初始關系生成笛卡爾積.
*/
foreach(r, joinrels[level - 1])//遍歷上一級生成的關系
{
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))//存在連接條件
{
/*
* 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相關的連接條件或連接順序限制，
* 因此僅規劃此rel與通過條件子句或約束條件鏈接在一起的初始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，所以不需要在關注鏈表中此rel前的rels;
* 在處理在此rel前的rels時,已處理這樣的連接.(make_join_rel函數自動處理鏡像連接)。
* level>2時，PG將上一級別生成的rels逐一與尚未處理的初始rel(存在連接條件或約束條件)進行連接.
*
*/
ListCell *other_rels;
if (level == 2) /* consider remaining initial rels */
other_rels = lnext(r);//level = 2,只需關注此rel之后的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);//創建連接
}
else//不存在連接條件
{
/*
* 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沒有連接條件(直接或通過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可能會出現重復處理的情況.
*/
make_rels_by_clauseless_joins(root,
old_rel,
list_head(joinrels[1]));//創建無條件連接
}
}
/*
* 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想連接.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.
* 這里只考慮存在連接條件(或者join-order限制)的關系對,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,只考慮余下的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不存在包含關系
{
/*
* 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))//存在連接條件或者join-order約束
{
(void) make_join_rel(root, old_rel, new_rel);//創建連接
}
}
}
}
}
/*----------
* 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.存在于外連接/IN(sub-SELECT)子查詢/LATERAL依賴/多關系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;//不考慮全外連接
/* 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].
* 創建old_rel和其他rel的連接(兩者存在連接條件)
*
* 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會通過多種方式生成同樣的連接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種方法會添加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只加入到合適的鏈表中
*
* '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:需要連接的rel
* other-rel:候選關系鏈表中的的第一個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,但其實對于連接生成的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)//遍歷鏈表
{
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不同而且存在連接關系&連接順序約束
{
(void) make_join_rel(root, old_rel, other_rel);//創建連接
}
}
}
//---------------------------------------------------- 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接條件
*
* 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:連接條件不一定是等值連接,
* 比如:SELECT * FROM a, b, c WHERE a.x = (b.y + c.z),只要a.x大于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鏈表較少的那個
*/
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;//存在連接條件
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);//存在等價類連接條件
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是否需要連接以滿足join-order限制(由于special/lateral連接引起)
*
* 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，因此可以與該函數合并，
* 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，
* 必須執行無語法連接以滿足連接順序限制。
* 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，那么我們應該考慮加入它們，即使連接是無連接條件的。
*
* 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:只有當簡并外部連接的一側包含多個rels時，
* 或者在IN/EXISTS RHS中需要一個無修飾的連接時，才會出現這個問題;
* 否則，將通過join_search_one_level()中的“last ditch”
* 找到連接路徑。如果愿意在“稠密計劃”的情況下進行大量的嘗試，
* 那么可以省去這個測試，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)//遍歷連接鏈表
{
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;
}創建測試數據表并生成測試數據:
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);
測試腳本:
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語句的連接關系: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;
查看優化器信息(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,數組中有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函數,level=2,開始循環遍歷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函數
(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]由于存在等價類{a.c1 b.c1 c.c1 d.c1 e.c1 f.c1},因此這一步驟會兩兩連接構造新的關系,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]調用make_join_rel函數后,查看root->join_rel_level[2],relids=6=2+4,這是1號(關系a)和2號(關系b)RTE的連接.
(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
$10 = 6[level=2]繼續循環,下幾組分別是ac,ad,ae,af
(gdb) p *$tmp->relids->words $12 = 18/34/66/130
[level=2]完成對關系a的兩兩連接
(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,兩兩形成連接,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的調用,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的調用
(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(兩兩連接形成的新關系)
(gdb) 83 foreach(r, joinrels[level - 1])
[level=3]與level=2不同,選擇初始的RelOptInfo進行連接,而不是同級的rels
... (gdb) 108 other_rels = list_head(joinrels[1]);
[level=3]完成第一輪的循環,root->join_rel_level[3]鏈表中有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]完成所有循環后的root->join_rel_level[3],構成連接的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,退出循環
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的調用,開始level 4調用
(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]完成第一輪循環調用,查看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]所有循環后的root->join_rel_level[4],構成連接的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級關系,k=other_level,同一層次的rel,兩兩組合,即1&2,3&4等嘗試兩兩配對連接
(gdb) n 153 foreach(r, joinrels[k]) ... (gdb) 168 if (k == other_level)
[level=4]如relids=6和relids=48的兩個關系
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]構造新的關系,但該關系無法通過合法連接形成或者已存在,因此沒有對root->join_rel_level[4]有所影響(調用前后均為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調用
(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]完成第一輪循環調用,查看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]所有循環后的root->join_rel_level[5],構成連接的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連接生成的關系 join 3個rels連接生成的關系
完成調用
(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調用
(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連接后,形成1個新的關系
(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連接生成的關系 join 4個rels連接生成的關系 & 3 join 3
完成調用,生成level=6的結果鏈表
(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]查看訪問路徑
(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
$99 = {path = {type = T_NestPath, pathtype = T_NestLoop, parent = 0x31047f8, pathtarget = 0x3104a08, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 2, startup_cost = 101.1725,
total_cost = 2218.2350000000001, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = false,
outerjoinpath = 0x2fccd80, innerjoinpath = 0x3107820, joinrestrictinfo = 0x3107ae0}該path的innerjoinpath(構造該連接inner關系的path)和outerjoinpath(構造該連接outer關系的path)
(gdb) p *$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}到此，關于“PostgreSQL中使用動態規劃算法構造連接路徑的實現函數是哪個”的學習就結束了，希望能夠解決大家的疑惑。理論與實踐的搭配能更好的幫助大家學習，快去試試吧！若想繼續學習更多相關知識，請繼續關注億速云網站，小編會繼續努力為大家帶來更多實用的文章！
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