本节介绍了创建计划create_plan函数中连接(join)计划的实现过程，主要的逻辑在函数create_join_plan中实现。
一、数据结构
Plan
所有计划节点通过将Plan结构作为第一个字段从Plan结构“派生”。这确保了在将节点转换为计划节点时能正常工作。(在执行器中以通用方式传递时，节点指针经常被转换为Plan *)
/* ----------------
* Plan node
*
* All plan nodes "derive" from the Plan structure by having the
* Plan structure as the first field. This ensures that everything works
* when nodes are cast to Plan's. (node pointers are frequently cast to Plan*
* when passed around generically in the executor)
* 所有计划节点通过将Plan结构作为第一个字段从Plan结构“派生”。
* 这确保了在将节点转换为计划节点时，一切都能正常工作。
* (在执行器中以通用方式传递时，节点指针经常被转换为Plan *)
*
* We never actually instantiate any Plan nodes; this is just the common
* abstract superclass for all Plan-type nodes.
* 从未实例化任何Plan节点;这只是所有Plan-type节点的通用抽象超类。
* ----------------
*/
typedef struct Plan
{
NodeTag type;//节点类型
/*
* 成本估算信息;estimated execution costs for plan (see costsize.c for more info)
*/
Cost startup_cost; /* 启动成本;cost expended before fetching any tuples */
Cost total_cost; /* 总成本;total cost (assuming all tuples fetched) */
/*
* 优化器估算信息;planner's estimate of result size of this plan step
*/
double plan_rows; /* 行数;number of rows plan is expected to emit */
int plan_width; /* 平均行大小(Byte为单位);average row width in bytes */
/*
* 并行执行相关的信息;information needed for parallel query
*/
bool parallel_aware; /* 是否参与并行执行逻辑?engage parallel-aware logic? */
bool parallel_safe; /* 是否并行安全;OK to use as part of parallel plan? */
/*
* Plan类型节点通用的信息.Common structural data for all Plan types.
*/
int plan_node_id; /* unique across entire final plan tree */
List *targetlist; /* target list to be computed at this node */
List *qual; /* implicitly-ANDed qual conditions */
struct Plan *lefttree; /* input plan tree(s) */
struct Plan *righttree;
List *initPlan; /* Init Plan nodes (un-correlated expr
* subselects) */
/*
* Information for management of parameter-change-driven rescanning
* parameter-change-driven重扫描的管理信息.
*
* extParam includes the paramIDs of all external PARAM_EXEC params
* affecting this plan node or its children. setParam params from the
* node's initPlans are not included, but their extParams are.
*
* allParam includes all the extParam paramIDs, plus the IDs of local
* params that affect the node (i.e., the setParams of its initplans).
* These are _all_ the PARAM_EXEC params that affect this node.
*/
Bitmapset *extParam;
Bitmapset *allParam;
} Plan;
二、源码解读
create_join_plan函数创建Join Plan节点.Join可以分为Merge Join/Hash Join/NestLoop Join三种,相应的实现函数是create_nestloop_plan/create_mergejoin_plan/create_hashjoin_plan.
//------------------------------------------------------------------ create_join_plan
/*
* create_join_plan
* Create a join plan for 'best_path' and (recursively) plans for its
* inner and outer paths.
* 创建连接计划Plan节点.
*/
static Plan *
create_join_plan(PlannerInfo *root, JoinPath *best_path)
{
Plan *plan;
List *gating_clauses;
switch (best_path->path.pathtype)
{
case T_MergeJoin://Merge Join
plan = (Plan *) create_mergejoin_plan(root,
(MergePath *) best_path);
break;
case T_HashJoin://Hash Join
plan = (Plan *) create_hashjoin_plan(root,
(HashPath *) best_path);
break;
case T_NestLoop://NestLoop Join
plan = (Plan *) create_nestloop_plan(root,
(NestPath *) best_path);
break;
default://目前仅支持上述三种
elog(ERROR, "unrecognized node type: %d",
(int) best_path->path.pathtype);
plan = NULL; /* keep compiler quiet */
break;
}
/*
* If there are any pseudoconstant clauses attached to this node, insert a
* gating Result node that evaluates the pseudoconstants as one-time
* quals.
* 如果这个节点上附加了伪常量子句，插入一个gating Result节点，该节点将伪常量计算为一次性条件quals。
*/
gating_clauses = get_gating_quals(root, best_path->joinrestrictinfo);
if (gating_clauses)
plan = create_gating_plan(root, (Path *) best_path, plan,
gating_clauses);
#ifdef NOT_USED
/*
* * Expensive function pullups may have pulled local predicates * into
* this path node. Put them in the qpqual of the plan node. * JMH,
* 6/15/92
* pullups函数可能已经把本地谓词上拉到该访问路径节点中,把这些信息放在Plan节点的qpqual中
*/
if (get_loc_restrictinfo(best_path) != NIL)
set_qpqual((Plan) plan,
list_concat(get_qpqual((Plan) plan),
get_actual_clauses(get_loc_restrictinfo(best_path))));
#endif
return plan;
}
//------------------------------------------ create_nestloop_plan
static NestLoop *
create_nestloop_plan(PlannerInfo *root,
NestPath *best_path)
{
NestLoop *join_plan;
Plan *outer_plan;
Plan *inner_plan;
List *tlist = build_path_tlist(root, &best_path->path);
List *joinrestrictclauses = best_path->joinrestrictinfo;
List *joinclauses;
List *otherclauses;
Relids outerrelids;
List *nestParams;
Relids saveOuterRels = root->curOuterRels;
ListCell *cell;
ListCell *prev;
ListCell *next;
/* NestLoop can project, so no need to be picky about child tlists */
//NestLoop可以执行投影操作,所以不需要关心子计划的tlists
//递归调用生成外表计划
outer_plan = create_plan_recurse(root, best_path->outerjoinpath, 0);
/* For a nestloop, include outer relids in curOuterRels for inner side */
//对于nestloop,对应内侧的curOuterRels中需要包含外表的relids
root->curOuterRels = bms_union(root->curOuterRels,
best_path->outerjoinpath->parent->relids);
//递归调用生成内表计划
inner_plan = create_plan_recurse(root, best_path->innerjoinpath, 0);
/* Restore curOuterRels */
//恢复curOuterRels
bms_free(root->curOuterRels);
root->curOuterRels = saveOuterRels;
/* Sort join qual clauses into best execution order */
//排序连接条件
joinrestrictclauses = order_qual_clauses(root, joinrestrictclauses);
/* Get the join qual clauses (in plain expression form) */
/* Any pseudoconstant clauses are ignored here */
//获取连接条件子句,在这里,会忽略伪常量
if (IS_OUTER_JOIN(best_path->jointype))
{
extract_actual_join_clauses(joinrestrictclauses,
best_path->path.parent->relids,
&joinclauses, &otherclauses);//外连接
}
else
{
/* We can treat all clauses alike for an inner join */
//内连接
joinclauses = extract_actual_clauses(joinrestrictclauses, false);
otherclauses = NIL;
}
/* Replace any outer-relation variables with nestloop params */
//使用nestloop参数替代外表变量
if (best_path->path.param_info)
{
joinclauses = (List *)
replace_nestloop_params(root, (Node *) joinclauses);
otherclauses = (List *)
replace_nestloop_params(root, (Node *) otherclauses);
}
/*
* Identify any nestloop parameters that should be supplied by this join
* node, and move them from root->curOuterParams to the nestParams list.
* 确定这个连接节点应该提供的所有nestloop连接参数，
* 并将它们从root->curOuterParams移动到nestParams链表中。
*/
outerrelids = best_path->outerjoinpath->parent->relids;
nestParams = NIL;
prev = NULL;
for (cell = list_head(root->curOuterParams); cell; cell = next)//遍历curOuterParams
{
NestLoopParam *nlp = (NestLoopParam *) lfirst(cell);//获取参数
next = lnext(cell);
if (IsA(nlp->paramval, Var) &&
bms_is_member(nlp->paramval->varno, outerrelids))//Var变量,而且是外层的relids
{
root->curOuterParams = list_delete_cell(root->curOuterParams,
cell, prev);
nestParams = lappend(nestParams, nlp);
}
else if (IsA(nlp->paramval, PlaceHolderVar) &&//PHV
bms_overlap(((PlaceHolderVar *) nlp->paramval)->phrels,
outerrelids) &&
bms_is_subset(find_placeholder_info(root,
(PlaceHolderVar *) nlp->paramval,
false)->ph_eval_at,
outerrelids))
{
root->curOuterParams = list_delete_cell(root->curOuterParams,
cell, prev);
nestParams = lappend(nestParams, nlp);
}
else
prev = cell;//直接赋值
}
join_plan = make_nestloop(tlist,
joinclauses,
otherclauses,
nestParams,
outer_plan,
inner_plan,
best_path->jointype,
best_path->inner_unique);//构造nestloop访问节点
copy_generic_path_info(&join_plan->join.plan, &best_path->path);
return join_plan;
}
//------------------------------------------ create_mergejoin_plan
static MergeJoin *
create_mergejoin_plan(PlannerInfo *root,
MergePath *best_path)
{
MergeJoin *join_plan;
Plan *outer_plan;
Plan *inner_plan;
List *tlist = build_path_tlist(root, &best_path->jpath.path);
List *joinclauses;
List *otherclauses;
List *mergeclauses;
List *outerpathkeys;
List *innerpathkeys;
int nClauses;
Oid *mergefamilies;
Oid *mergecollations;
int *mergestrategies;
bool *mergenullsfirst;
PathKey *opathkey;
EquivalenceClass *opeclass;
int i;
ListCell *lc;
ListCell *lop;
ListCell *lip;
Path *outer_path = best_path->jpath.outerjoinpath;
Path *inner_path = best_path->jpath.innerjoinpath;
/*
* MergeJoin can project, so we don't have to demand exact tlists from the
* inputs. However, if we're intending to sort an input's result, it's
* best to request a small tlist so we aren't sorting more data than
* necessary.
* MergeJoin可以进行投影运算，因此不必从输入中要求精确的tlist。
* 然而，如果打算对输入的结果进行排序，最好是请求一个小的tlist，这样就不会对多余的数据进行排序。
*/
//对外表生成计划Plan
outer_plan = create_plan_recurse(root, best_path->jpath.outerjoinpath,
(best_path->outersortkeys != NIL) ? CP_SMALL_TLIST : 0);
//对内部生成计划Plan
inner_plan = create_plan_recurse(root, best_path->jpath.innerjoinpath,
(best_path->innersortkeys != NIL) ? CP_SMALL_TLIST : 0);
/* Sort join qual clauses into best execution order */
/* NB: do NOT reorder the mergeclauses */
//排序连接条件
joinclauses = order_qual_clauses(root, best_path->jpath.joinrestrictinfo);
/* Get the join qual clauses (in plain expression form) */
/* Any pseudoconstant clauses are ignored here */
//获取连接约束条件子句(以扁平化的形式)
if (IS_OUTER_JOIN(best_path->jpath.jointype))
{
extract_actual_join_clauses(joinclauses,
best_path->jpath.path.parent->relids,
&joinclauses, &otherclauses);
}
else
{
/* We can treat all clauses alike for an inner join */
//以内连接的方式处理所有条件子句
joinclauses = extract_actual_clauses(joinclauses, false);
otherclauses = NIL;
}
/*
* Remove the mergeclauses from the list of join qual clauses, leaving the
* list of quals that must be checked as qpquals.
* 从join qual子句链表中删除mergeclauses，将必须检查为qpquals的quals链表保留下来。
*/
mergeclauses = get_actual_clauses(best_path->path_mergeclauses);
joinclauses = list_difference(joinclauses, mergeclauses);
/*
* Replace any outer-relation variables with nestloop params. There
* should not be any in the mergeclauses.
* 使用nestloop参数替代外表变量.这些变量不应在mergeclauses中出现.
*/
if (best_path->jpath.path.param_info)
{
joinclauses = (List *)
replace_nestloop_params(root, (Node *) joinclauses);//连接条件
otherclauses = (List *)
replace_nestloop_params(root, (Node *) otherclauses);//其他条件
}
/*
* Rearrange mergeclauses, if needed, so that the outer variable is always
* on the left; mark the mergeclause restrictinfos with correct
* outer_is_left status.
* 如果需要，重新安排mergeclauses，使外部变量总是在左边;
* 用正确的outer_is_left状态标记mergeclause restrictinfos。
*/
mergeclauses = get_switched_clauses(best_path->path_mergeclauses,
best_path->jpath.outerjoinpath->parent->relids);
/*
* Create explicit sort nodes for the outer and inner paths if necessary.
* 如需要创建显式的Sort节点
*/
if (best_path->outersortkeys)
{
Relids outer_relids = outer_path->parent->relids;
Sort *sort = make_sort_from_pathkeys(outer_plan,
best_path->outersortkeys,
outer_relids);
label_sort_with_costsize(root, sort, -1.0);
outer_plan = (Plan *) sort;
outerpathkeys = best_path->outersortkeys;
}
else
outerpathkeys = best_path->jpath.outerjoinpath->pathkeys;
if (best_path->innersortkeys)
{
Relids inner_relids = inner_path->parent->relids;
Sort *sort = make_sort_from_pathkeys(inner_plan,
best_path->innersortkeys,
inner_relids);
label_sort_with_costsize(root, sort, -1.0);
inner_plan = (Plan *) sort;
innerpathkeys = best_path->innersortkeys;
}
else
innerpathkeys = best_path->jpath.innerjoinpath->pathkeys;
/*
* If specified, add a materialize node to shield the inner plan from the
* need to handle mark/restore.
* 如指定物化,则添加物化节点
*/
if (best_path->materialize_inner)
{
Plan *matplan = (Plan *) make_material(inner_plan);
/*
* We assume the materialize will not spill to disk, and therefore
* charge just cpu_operator_cost per tuple. (Keep this estimate in
* sync with final_cost_mergejoin.)
* 假设materialize不会溢出到磁盘，因此每个元组的成本为cpu_operator_cost。
* (让这个估计与final_cost_mergejoin保持同步。)
*/
copy_plan_costsize(matplan, inner_plan);
matplan->total_cost += cpu_operator_cost * matplan->plan_rows;
inner_plan = matplan;
}
/*
* Compute the opfamily/collation/strategy/nullsfirst arrays needed by the
* executor. The information is in the pathkeys for the two inputs, but
* we need to be careful about the possibility of mergeclauses sharing a
* pathkey, as well as the possibility that the inner pathkeys are not in
* an order matching the mergeclauses.
* 计算执行器需要的opfamily/collation/strategy/nullsfirst数组。
* 信息在这两个输入的pathkeys中，但是需要注意mergeclauses共享一个pathkey的可能性，
* 以及内表路径键不符合mergeclauses顺序的可能性。
*/
nClauses = list_length(mergeclauses);
Assert(nClauses == list_length(best_path->path_mergeclauses));
mergefamilies = (Oid *) palloc(nClauses * sizeof(Oid));//申请内存
mergecollations = (Oid *) palloc(nClauses * sizeof(Oid));
mergestrategies = (int *) palloc(nClauses * sizeof(int));
mergenullsfirst = (bool *) palloc(nClauses * sizeof(bool));
opathkey = NULL;
opeclass = NULL;
lop = list_head(outerpathkeys);
lip = list_head(innerpathkeys);
i = 0;
foreach(lc, best_path->path_mergeclauses)//遍历条件
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
EquivalenceClass *oeclass;
EquivalenceClass *ieclass;
PathKey *ipathkey = NULL;
EquivalenceClass *ipeclass = NULL;
bool first_inner_match = false;
/* fetch outer/inner eclass from mergeclause */
//从mergeclause中获取outer/inner等价类
if (rinfo->outer_is_left)
{
oeclass = rinfo->left_ec;
ieclass = rinfo->right_ec;
}
else
{
oeclass = rinfo->right_ec;
ieclass = rinfo->left_ec;
}
Assert(oeclass != NULL);
Assert(ieclass != NULL);
/*
* We must identify the pathkey elements associated with this clause
* by matching the eclasses (which should give a unique match, since
* the pathkey lists should be canonical). In typical cases the merge
* clauses are one-to-one with the pathkeys, but when dealing with
* partially redundant query conditions, things are more complicated.
* 必须通过匹配等价类eclasses来标识与此子句关联的pathkey元素
* (它应该提供唯一的匹配，因为pathkey链表应该是规范的)。
* 在典型的情况下，merge子句与pathkey是一对一的，但是在处理部分冗余查询条件时，事情就有些复杂了。
*
* lop and lip reference the first as-yet-unmatched pathkey elements.
* If they're NULL then all pathkey elements have been matched.
* lop和lip引用第一个尚未匹配的pathkey元素。如果它们为空，那么所有的pathkey元素都已匹配。
*
* The ordering of the outer pathkeys should match the mergeclauses,
* by construction (see find_mergeclauses_for_outer_pathkeys()). There
* could be more than one mergeclause for the same outer pathkey, but
* no pathkey may be entirely skipped over.
* 通过处理，外表pathkey顺序应该与mergeclauses匹配(参见find_mergeclauses_for_outer_pathkeys()函数)。
* 同一个外表pathkey可以有多个mergeclause，但是不能完全跳过所有pathkey。
*/
if (oeclass != opeclass) /* multiple matches are not interesting */
{
/* doesn't match the current opathkey, so must match the next */
//与当前的opathkey不匹配,那么必须与接下来的匹配
if (lop == NULL)
elog(ERROR, "outer pathkeys do not match mergeclauses");
opathkey = (PathKey *) lfirst(lop);
opeclass = opathkey->pk_eclass;
lop = lnext(lop);
if (oeclass != opeclass)
elog(ERROR, "outer pathkeys do not match mergeclauses");
}
/*
* The inner pathkeys likewise should not have skipped-over keys, but
* it's possible for a mergeclause to reference some earlier inner
* pathkey if we had redundant pathkeys. For example we might have
* mergeclauses like "o.a = i.x AND o.b = i.y AND o.c = i.x". The
* implied inner ordering is then "ORDER BY x, y, x", but the pathkey
* mechanism drops the second sort by x as redundant, and this code
* must cope.
* 同样，内表pathkey也不应该有skipped-over keys，但是如果我们有冗余的路径键，
* mergeclause可以引用一些早期的内部路径键。
* 例如，我们可能存在下面的mergeclauses，比如"o.a = i.x AND o.b = i.y AND o.c = i.x"。
* 隐含的内部排序是“x, y, x的排序”，但是pathkey机制将按x排序视为多余并删除，在这里必须处理这种情况。
*
* It's also possible for the implied inner-rel ordering to be like
* "ORDER BY x, y, x DESC". We still drop the second instance of x as
* redundant; but this means that the sort ordering of a redundant
* inner pathkey should not be considered significant. So we must
* detect whether this is the first clause matching an inner pathkey.
* 对于隐含的内表排序，也有可能是“ORDER BY x, y, x DESC”。
* 仍然将x的第二个实例视为冗余并删除;
* 但是这意味着冗余的内表pathkey的排序顺序不应该被认为是重要的。
* 因此，我们必须检测这是否是与内表pathkey匹配的第一个子句。
*
*/
if (lip)
{
ipathkey = (PathKey *) lfirst(lip);
ipeclass = ipathkey->pk_eclass;
if (ieclass == ipeclass)
{
/* successful first match to this inner pathkey */
//成功匹配
lip = lnext(lip);
first_inner_match = true;
}
}
if (!first_inner_match)
{
/* redundant clause ... must match something before lip */
//多余的条件子句,必须在lip前匹配某些pathkey
ListCell *l2;
foreach(l2, innerpathkeys)
{
if (l2 == lip)
break;
ipathkey = (PathKey *) lfirst(l2);
ipeclass = ipathkey->pk_eclass;
if (ieclass == ipeclass)
break;
}
if (ieclass != ipeclass)
elog(ERROR, "inner pathkeys do not match mergeclauses");
}
/*
* The pathkeys should always match each other as to opfamily and
* collation (which affect equality), but if we're considering a
* redundant inner pathkey, its sort ordering might not match. In
* such cases we may ignore the inner pathkey's sort ordering and use
* the outer's. (In effect, we're lying to the executor about the
* sort direction of this inner column, but it does not matter since
* the run-time row comparisons would only reach this column when
* there's equality for the earlier column containing the same eclass.
* There could be only one value in this column for the range of inner
* rows having a given value in the earlier column, so it does not
* matter which way we imagine this column to be ordered.) But a
* non-redundant inner pathkey had better match outer's ordering too.
* 对于opfamily和collation(这会影响等式)，pathkey应该总是匹配的，
* 但是如果我们考虑一个冗余的内表pathkey，它的排序顺序可能不匹配。
* 在这种情况下，我们可以忽略内表pathkey的排序顺序，而使用外表访问路径。
* (实际上，是在内表列的排序方向上欺骗执行器，但这无关紧要，
* 因为运行时行比较只在包含相同eclass的前一列相等时才会到达这一列。
* 对于在前一列中具有给定值的内部行范围，在此列中只能有一个值，
* 因此我们认为该列的顺序如何并不重要。)
* 而一个非冗余的内部路径也最好与外部的排序匹配。
*/
if (opathkey->pk_opfamily != ipathkey->pk_opfamily ||
opathkey->pk_eclass->ec_collation != ipathkey->pk_eclass->ec_collation)
elog(ERROR, "left and right pathkeys do not match in mergejoin");
if (first_inner_match &&
(opathkey->pk_strategy != ipathkey->pk_strategy ||
opathkey->pk_nulls_first != ipathkey->pk_nulls_first))
elog(ERROR, "left and right pathkeys do not match in mergejoin");
/* OK, save info for executor */
mergefamilies[i] = opathkey->pk_opfamily;
mergecollations[i] = opathkey->pk_eclass->ec_collation;
mergestrategies[i] = opathkey->pk_strategy;
mergenullsfirst[i] = opathkey->pk_nulls_first;
i++;
}
/*
* Note: it is not an error if we have additional pathkey elements (i.e.,
* lop or lip isn't NULL here). The input paths might be better-sorted
* than we need for the current mergejoin.
* 注意:如果有额外的pathkey元素(例如， lop或lip在这里不是空的)。
* 输入路径可能比当前合并连接所需的排序更好。
*/
/*
* Now we can build the mergejoin node.
* 创建mergejoin节点
*/
join_plan = make_mergejoin(tlist,
joinclauses,
otherclauses,
mergeclauses,
mergefamilies,
mergecollations,
mergestrategies,
mergenullsfirst,
outer_plan,
inner_plan,
best_path->jpath.jointype,
best_path->jpath.inner_unique,
best_path->skip_mark_restore);
/* Costs of sort and material steps are included in path cost already */
//排序和物化步骤一包含在访问路径的成本中
copy_generic_path_info(&join_plan->join.plan, &best_path->jpath.path);
return join_plan;
}
//------------------------------------------ create_hashjoin_plan
static HashJoin *
create_hashjoin_plan(PlannerInfo *root,
HashPath *best_path)
{
HashJoin *join_plan;
Hash *hash_plan;
Plan *outer_plan;
Plan *inner_plan;
List *tlist = build_path_tlist(root, &best_path->jpath.path);
List *joinclauses;
List *otherclauses;
List *hashclauses;
Oid skewTable = InvalidOid;
AttrNumber skewColumn = InvalidAttrNumber;
bool skewInherit = false;
/*
* HashJoin can project, so we don't have to demand exact tlists from the
* inputs. However, it's best to request a small tlist from the inner
* side, so that we aren't storing more data than necessary. Likewise, if
* we anticipate batching, request a small tlist from the outer side so
* that we don't put extra data in the outer batch files.
* HashJoin可以进行投影运算，因此我们不必从输入中要求精确的tlist。
* 但是，最好从内部请求一个小tlist，这样就不需要存储过多的数据。
* 同样，如果我们进行预批处理，从外部请求一个小tlist，这样就不会在外部批处理文件中添加额外的数据。
*/
outer_plan = create_plan_recurse(root, best_path->jpath.outerjoinpath,
(best_path->num_batches > 1) ? CP_SMALL_TLIST : 0);
inner_plan = create_plan_recurse(root, best_path->jpath.innerjoinpath,
CP_SMALL_TLIST);
/* Sort join qual clauses into best execution order */
joinclauses = order_qual_clauses(root, best_path->jpath.joinrestrictinfo);
/* There's no point in sorting the hash clauses ... */
/* Get the join qual clauses (in plain expression form) */
/* Any pseudoconstant clauses are ignored here */
if (IS_OUTER_JOIN(best_path->jpath.jointype))
{
extract_actual_join_clauses(joinclauses,
best_path->jpath.path.parent->relids,
&joinclauses, &otherclauses);
}
else
{
/* We can treat all clauses alike for an inner join */
joinclauses = extract_actual_clauses(joinclauses, false);
otherclauses = NIL;
}
/*
* Remove the hashclauses from the list of join qual clauses, leaving the
* list of quals that must be checked as qpquals.
* 从join qual子句列表中删除hashclause，将必须检查为qpquals的quals列表保留下来。
*/
hashclauses = get_actual_clauses(best_path->path_hashclauses);
joinclauses = list_difference(joinclauses, hashclauses);
/*
* Replace any outer-relation variables with nestloop params. There
* should not be any in the hashclauses.
* 用nestloop参数替换任何外部关系变量。而且不应在hashclauses中出现。
*/
if (best_path->jpath.path.param_info)
{
joinclauses = (List *)
replace_nestloop_params(root, (Node *) joinclauses);
otherclauses = (List *)
replace_nestloop_params(root, (Node *) otherclauses);
}
/*
* Rearrange hashclauses, if needed, so that the outer variable is always
* on the left.
* 重新安排hashclausees,以便外表的Var出现在左侧
*/
hashclauses = get_switched_clauses(best_path->path_hashclauses,
best_path->jpath.outerjoinpath->parent->relids);
/*
* If there is a single join clause and we can identify the outer variable
* as a simple column reference, supply its identity for possible use in
* skew optimization. (Note: in principle we could do skew optimization
* with multiple join clauses, but we'd have to be able to determine the
* most common combinations of outer values, which we don't currently have
* enough stats for.)
* 如果有一个连接条件子句，并且可以将外表变量标识为一个简单的列引用，
* 那么可以通过提供它的标识以表在列数据倾斜优化中使用。
* (注意:原则上可以使用多个连接子句进行倾斜优化，
* 但我们必须能够确定最常见的外部值组合，目前我们还没有足够的统计数据。)
*/
if (list_length(hashclauses) == 1)
{
OpExpr *clause = (OpExpr *) linitial(hashclauses);
Node *node;
Assert(is_opclause(clause));
node = (Node *) linitial(clause->args);
if (IsA(node, RelabelType))
node = (Node *) ((RelabelType *) node)->arg;
if (IsA(node, Var))
{
Var *var = (Var *) node;
RangeTblEntry *rte;
rte = root->simple_rte_array[var->varno];
if (rte->rtekind == RTE_RELATION)
{
skewTable = rte->relid;
skewColumn = var->varattno;
skewInherit = rte->inh;
}
}
}
/*
* Build the hash node and hash join node.
* 创建hash节点和hash join节点
*/
hash_plan = make_hash(inner_plan,
skewTable,
skewColumn,
skewInherit);//为内表创建hash表
/*
* Set Hash node's startup & total costs equal to total cost of input
* plan; this only affects EXPLAIN display not decisions.
* 设置哈希节点的启动和总成本等于输入的计划总成本;
* 这只影响解释显示而不是决策。
*/
copy_plan_costsize(&hash_plan->plan, inner_plan);
hash_plan->plan.startup_cost = hash_plan->plan.total_cost;
/*
* If parallel-aware, the executor will also need an estimate of the total
* number of rows expected from all participants so that it can size the
* shared hash table.
* 如果需要并行，执行器还需要估计所有参与者预期的行数，以便对共享哈希表进行大小计算。
*/
if (best_path->jpath.path.parallel_aware)
{
hash_plan->plan.parallel_aware = true;
hash_plan->rows_total = best_path->inner_rows_total;
}
join_plan = make_hashjoin(tlist,
joinclauses,
otherclauses,
hashclauses,
outer_plan,
(Plan *) hash_plan,
best_path->jpath.jointype,
best_path->jpath.inner_unique);//创建hash join节点
copy_generic_path_info(&join_plan->join.plan, &best_path->jpath.path);
return join_plan;
}
三、跟踪分析
测试脚本如下
testdb=# explain select dw.*,grjf.grbh,grjf.xm,grjf.ny,grjf.je
testdb-# from t_dwxx dw,lateral (select gr.grbh,gr.xm,jf.ny,jf.je
testdb(# from t_grxx gr inner join t_jfxx jf
testdb(# on gr.dwbh = dw.dwbh
testdb(# and gr.grbh = jf.grbh) grjf
testdb-# where dw.dwbh in ('1001','1002')
testdb-# order by dw.dwbh;
QUERY PLAN
--------------------------------------------------------------------------------------------------
Sort (cost=2010.12..2010.17 rows=20 width=47)
Sort Key: dw.dwbh
-> Nested Loop (cost=14.24..2009.69 rows=20 width=47)
-> Hash Join (cost=13.95..2002.56 rows=20 width=32)
Hash Cond: ((gr.dwbh)::text = (dw.dwbh)::text)
-> Seq Scan on t_grxx gr (cost=0.00..1726.00 rows=100000 width=16)
-> Hash (cost=13.92..13.92 rows=2 width=20)
-> Index Scan using t_dwxx_pkey on t_dwxx dw (cost=0.29..13.92 rows=2 width=20)
Index Cond: ((dwbh)::text = ANY ('{1001,1002}'::text[]))
-> Index Scan using idx_t_jfxx_grbh on t_jfxx jf (cost=0.29..0.35 rows=1 width=20)
Index Cond: ((grbh)::text = (gr.grbh)::text)
启动gdb,设置断点,进入create_join_plan函数
(gdb) b create_join_plan
Breakpoint 1 at 0x7b8426: file createplan.c, line 973.
(gdb) c
Continuing.
Breakpoint 1, create_join_plan (root=0x2ef8a00, best_path=0x2f5ad40) at createplan.c:973
973 switch (best_path->path.pathtype)
查看输入参数,pathtype为T_NestLoop
(gdb) p *best_path
$3 = {path = {type = T_NestPath, pathtype = T_NestLoop, parent = 0x2f5a570, pathtarget = 0x2f5a788, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 20, startup_cost = 14.241722117799656,
total_cost = 2009.6908721177995, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = false,
outerjoinpath = 0x2f58bb0, innerjoinpath = 0x2f56080, joinrestrictinfo = 0x0}
进入create_nestloop_plan
973 switch (best_path->path.pathtype)
(gdb) n
984 plan = (Plan *) create_nestloop_plan(root,
(gdb) step
create_nestloop_plan (root=0x2f49180, best_path=0x2f5ad40) at createplan.c:3678
3678 List *tlist = build_path_tlist(root, &best_path->path);
nestloop join->创建tlist,获取连接条件等
3678 List *tlist = build_path_tlist(root, &best_path->path);
(gdb) n
3679 List *joinrestrictclauses = best_path->joinrestrictinfo;
(gdb)
3684 Relids saveOuterRels = root->curOuterRels;
(gdb) p root->curOuterRels
$1 = (Relids) 0x0
nestloop join->调用create_plan_recurse创建outer_plan
(gdb) n
3690 outer_plan = create_plan_recurse(root, best_path->outerjoinpath, 0);
(gdb)
Breakpoint 1, create_join_plan (root=0x2f49180, best_path=0x2f58bb0) at createplan.c:973
973 switch (best_path->path.pathtype)
nestloop join->外表对应的outer_plan为T_HashJoin
(gdb) p *best_path
$2 = {path = {type = T_HashPath, pathtype = T_HashJoin, parent = 0x2f572d0, pathtarget = 0x2f57508, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 20, startup_cost = 13.949222117799655,
total_cost = 2002.5604721177997, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = true,
outerjoinpath = 0x2f512f0, innerjoinpath = 0x2f51e98, joinrestrictinfo = 0x2f577a8}
(gdb)
nestloop join->进入create_hashjoin_plan
(gdb) n
980 plan = (Plan *) create_hashjoin_plan(root,
(gdb) step
create_hashjoin_plan (root=0x2f49180, best_path=0x2f58bb0) at createplan.c:4093
4093 List *tlist = build_path_tlist(root, &best_path->jpath.path);
hash join->创建outer plan
(gdb)
4108 outer_plan = create_plan_recurse(root, best_path->jpath.outerjoinpath,
(gdb) p *best_path->jpath.outerjoinpath
$4 = {type = T_Path, pathtype = T_SeqScan, parent = 0x2f06090, pathtarget = 0x2f062c8, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000, startup_cost = 0, total_cost = 1726,
pathkeys = 0x0}
hash join->创建inner plan
(gdb) p *best_path->jpath.innerjoinpath
$5 = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2f04b60, pathtarget = 0x2f04d98, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 2, startup_cost = 0.28500000000000003,
total_cost = 13.924222117799655, pathkeys = 0x2f51e20}
hash join->获取连接条件
(gdb) n
4115 joinclauses = order_qual_clauses(root, best_path->jpath.joinrestrictinfo);
(gdb)
4120 if (IS_OUTER_JOIN(best_path->jpath.jointype))
(gdb) p *joinclauses
$6 = {type = T_List, length = 1, head = 0x2f57780, tail = 0x2f57780}
hash join->处理连接条件&hash条件
(gdb) n
4137 hashclauses = get_actual_clauses(best_path->path_hashclauses);
(gdb)
4138 joinclauses = list_difference(joinclauses, hashclauses);
(gdb)
4144 if (best_path->jpath.path.param_info)
(gdb) p *hashclauses
$8 = {type = T_List, length = 1, head = 0x2f5d690, tail = 0x2f5d690}
(gdb) p *joinclauses
Cannot access memory at address 0x0
hash join->变换位置,把外表的Var放在左侧
(gdb) n
4156 hashclauses = get_switched_clauses(best_path->path_hashclauses,
(gdb)
hash join->Hash连接条件只有一个,进行数据倾斜优化
(gdb)
4167 if (list_length(hashclauses) == 1)
(gdb) n
4169 OpExpr *clause = (OpExpr *) linitial(hashclauses);
(gdb) n
4172 Assert(is_opclause(clause));
(gdb)
4173 node = (Node *) linitial(clause->args);
(gdb)
4174 if (IsA(node, RelabelType))
(gdb)
4175 node = (Node *) ((RelabelType *) node)->arg;
(gdb)
4176 if (IsA(node, Var))
(gdb)
4178 Var *var = (Var *) node;
(gdb)
4181 rte = root->simple_rte_array[var->varno];
(gdb) p *node
$9 = {type = T_Var}
(gdb) p *(Var *)node
$10 = {xpr = {type = T_Var}, varno = 3, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 3, varoattno = 1, location = 208}
(gdb) n
4182 if (rte->rtekind == RTE_RELATION)
(gdb)
4184 skewTable = rte->relid;
(gdb)
4185 skewColumn = var->varattno;
(gdb)
4186 skewInherit = rte->inh;
(gdb)
hash join->开始创建创建hash节点和hash join节点
创建hash节点(构建Hash表)
4194 hash_plan = make_hash(inner_plan,
(gdb) n
4203 copy_plan_costsize(&hash_plan->plan, inner_plan);
(gdb)
4204 hash_plan->plan.startup_cost = hash_plan->plan.total_cost;
(gdb) p *hash_plan
$11 = {plan = {type = T_Hash, startup_cost = 0.28500000000000003, total_cost = 13.924222117799655, plan_rows = 2,
plan_width = 20, parallel_aware = false, parallel_safe = true, plan_node_id = 0, targetlist = 0x2f5d250, qual = 0x0,
lefttree = 0x2f58428, righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}, skewTable = 16742,
skewColumn = 1, skewInherit = false, rows_total = 0}
hash join->创建hash join节点
(gdb) n
4217 join_plan = make_hashjoin(tlist,
(gdb)
4226 copy_generic_path_info(&join_plan->join.plan, &best_path->jpath.path);
(gdb)
4228 return join_plan;
(gdb) p *join_plan
$13 = {join = {plan = {type = T_HashJoin, startup_cost = 13.949222117799655, total_cost = 2002.5604721177997,
plan_rows = 20, plan_width = 32, parallel_aware = false, parallel_safe = true, plan_node_id = 0,
targetlist = 0x2f5cb28, qual = 0x0, lefttree = 0x2f5ae98, righttree = 0x2f5d830, initPlan = 0x0, extParam = 0x0,
allParam = 0x0}, jointype = JOIN_INNER, inner_unique = true, joinqual = 0x0}, hashclauses = 0x2f5d7f8}
hash join->回到create_nestloop_plan
(gdb) n
create_nestloop_plan (root=0x2f49180, best_path=0x2f5ad40) at createplan.c:3694
3694 best_path->outerjoinpath->parent->relids);
(gdb) n
3693 root->curOuterRels = bms_union(root->curOuterRels,
nestloop join->创建内表Plan
(gdb) n
3696 inner_plan = create_plan_recurse(root, best_path->innerjoinpath, 0);
(gdb) p *best_path->innerjoinpath
$16 = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2f06858, pathtarget = 0x2f06a70, param_info = 0x2f56910,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 1, startup_cost = 0.29249999999999998,
total_cost = 0.34651999999999999, pathkeys = 0x2f56608}
nestloop join->获取连接条件子句
(gdb) n
3699 bms_free(root->curOuterRels);
(gdb)
3700 root->curOuterRels = saveOuterRels;
(gdb)
3703 joinrestrictclauses = order_qual_clauses(root, joinrestrictclauses);
(gdb)
3707 if (IS_OUTER_JOIN(best_path->jointype))
(gdb) p *joinrestrictclauses
Cannot access memory at address 0x0
nestloop join->获取连接条件&参数化处理(相关值为NULL)
(gdb) n
3716 joinclauses = extract_actual_clauses(joinrestrictclauses, false);
(gdb)
3717 otherclauses = NIL;
(gdb)
3721 if (best_path->path.param_info)
(gdb) p *joinclauses
Cannot access memory at address 0x0
(gdb) p *best_path->path.param_info
Cannot access memory at address 0x0
nestloop join->获取外表的relids(外表为1和3号RTE的连接)
(gdb) n
3733 outerrelids = best_path->outerjoinpath->parent->relids;
(gdb)
3734 nestParams = NIL;
(gdb) p *outerrelids
$17 = {nwords = 1, words = 0x2f574ec}
(gdb) p *outerrelids->words
$18 = 10
nestloop join->遍历当前的外表参数链表
(gdb) n
3735 prev = NULL;
(gdb)
3736 for (cell = list_head(root->curOuterParams); cell; cell = next)
(gdb) p *root->curOuterParams
$19 = {type = T_List, length = 1, head = 0x2f5df98, tail = 0x2f5df98}
nestloop join->查看该参数信息,3号RTE编号为2的字段(即grbh)
(gdb) n
3738 NestLoopParam *nlp = (NestLoopParam *) lfirst(cell);
(gdb)
3740 next = lnext(cell);
(gdb) p *(NestLoopParam *)nlp
$21 = {type = T_NestLoopParam, paramno = 0, paramval = 0x2f54e50}
(gdb) p *nlp->paramval
$22 = {xpr = {type = T_Var}, varno = 3, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 3, varoattno = 2, location = 273}
nestloop join->把条件从root->curOuterParams移动到nestParams链表中
(gdb) n
3741 if (IsA(nlp->paramval, Var) &&
(gdb) n
3742 bms_is_member(nlp->paramval->varno, outerrelids))
(gdb)
3741 if (IsA(nlp->paramval, Var) &&
(gdb)
3744 root->curOuterParams = list_delete_cell(root->curOuterParams,
(gdb)
3746 nestParams = lappend(nestParams, nlp);
(gdb)
3736 for (cell = list_head(root->curOuterParams); cell; cell = next)
(gdb) p *nestParams
$23 = {type = T_List, length = 1, head = 0x2f5df98, tail = 0x2f5df98}
(gdb) p *(Node *)nestParams->head->data.ptr_value
$24 = {type = T_NestLoopParam}
(gdb) p *(NestLoopParam *)nestParams->head->data.ptr_value
$25 = {type = T_NestLoopParam, paramno = 0, paramval = 0x2f54e50}
(gdb) set $nlp=(NestLoopParam *)nestParams->head->data.ptr_value
(gdb) p $nlp->paramval
$26 = (Var *) 0x2f54e50
(gdb) p *$nlp->paramval
$27 = {xpr = {type = T_Var}, varno = 3, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 3, varoattno = 2, location = 273}
(gdb)
nestloop join->创建nestloop join节点
(gdb) n
3771 best_path->inner_unique);
(gdb)
3764 join_plan = make_nestloop(tlist,
(gdb)
3773 copy_generic_path_info(&join_plan->join.plan, &best_path->path);
(gdb)
3775 return join_plan;
(gdb) p *join_plan
$28 = {join = {plan = {type = T_NestLoop, startup_cost = 14.241722117799656, total_cost = 2009.6908721177995,
plan_rows = 20, plan_width = 47, parallel_aware = false, parallel_safe = true, plan_node_id = 0,
targetlist = 0x2f5c770, qual = 0x0, lefttree = 0x2f5d8c8, righttree = 0x2f59ed0, initPlan = 0x0, extParam = 0x0,
allParam = 0x0}, jointype = JOIN_INNER, inner_unique = false, joinqual = 0x0}, nestParams = 0x2f5dfc0}
(gdb)
DONE!
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