本篇内容介绍了“PostgreSQL中函数reconsider_outer_join_clauses的主要实现逻辑是什么”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
query_planner代码片段:
//... /* * Examine the targetlist and join tree, adding entries to baserel * targetlists for all referenced Vars, and generating PlaceHolderInfo * entries for all referenced PlaceHolderVars. Restrict and join clauses * are added to appropriate lists belonging to the mentioned relations. We * also build EquivalenceClasses for provably equivalent expressions. The * SpecialJoinInfo list is also built to hold information about join order * restrictions. Finally, we form a target joinlist for make_one_rel() to * work from. */ build_base_rel_tlists(root, tlist);//构建"base rels"的投影列 find_placeholders_in_jointree(root);//处理jointree中的PHI find_lateral_references(root);//处理jointree中Lateral依赖 joinlist = deconstruct_jointree(root);//分解jointree /* * Reconsider any postponed outer-join quals now that we have built up * equivalence classes. (This could result in further additions or * mergings of classes.) */ reconsider_outer_join_clauses(root);//已创建等价类,那么需要重新考虑被下推后处理的外连接表达式 /* * If we formed any equivalence classes, generate additional restriction * clauses as appropriate. (Implied join clauses are formed on-the-fly * later.) */ generate_base_implied_equalities(root);//等价类构建后,生成因此外加的约束语句 //...
一、重要的数据结构
RelOptInfo
与上节一样,RelOptInfo结构体贯彻逻辑优化和物理优化过程的始终,需不时Review.
typedef struct RelOptInfo
{
NodeTag type;//节点标识
RelOptKind reloptkind;//RelOpt类型
/* all relations included in this RelOptInfo */
Relids relids; /*Relids(rtindex)集合 set of base relids (rangetable indexes) */
/* size estimates generated by planner */
double rows; /*结果元组的估算数量 estimated number of result tuples */
/* per-relation planner control flags */
bool consider_startup; /*是否考虑启动成本?是,需要保留启动成本低的路径 keep cheap-startup-cost paths? */
bool consider_param_startup; /*是否考虑参数化?的路径 ditto, for parameterized paths? */
bool consider_parallel; /*是否考虑并行处理路径 consider parallel paths? */
/* default result targetlist for Paths scanning this relation */
struct PathTarget *reltarget; /*扫描该Relation时默认的结果 list of Vars/Exprs, cost, width */
/* materialization information */
List *pathlist; /*访问路径链表 Path structures */
List *ppilist; /*路径链表中使用参数化路径进行 ParamPathInfos used in pathlist */
List *partial_pathlist; /* partial Paths */
struct Path *cheapest_startup_path;//代价最低的启动路径
struct Path *cheapest_total_path;//代价最低的整体路径
struct Path *cheapest_unique_path;//代价最低的获取唯一值的路径
List *cheapest_parameterized_paths;//代价最低的参数化?路径链表
/* parameterization information needed for both base rels and join rels */
/* (see also lateral_vars and lateral_referencers) */
Relids direct_lateral_relids; /*使用lateral语法,需依赖的Relids rels directly laterally referenced */
Relids lateral_relids; /* minimum parameterization of rel */
/* information about a base rel (not set for join rels!) */
//reloptkind=RELOPT_BASEREL时使用的数据结构
Index relid; /* Relation ID */
Oid reltablespace; /* 表空间 containing tablespace */
RTEKind rtekind; /* 基表?子查询?还是函数等等?RELATION, SUBQUERY, FUNCTION, etc */
AttrNumber min_attr; /* 最小的属性编号 smallest attrno of rel (often <0) */
AttrNumber max_attr; /* 最大的属性编号 largest attrno of rel */
Relids *attr_needed; /* 数组 array indexed [min_attr .. max_attr] */
int32 *attr_widths; /* 属性宽度 array indexed [min_attr .. max_attr] */
List *lateral_vars; /* 关系依赖的Vars/PHVs LATERAL Vars and PHVs referenced by rel */
Relids lateral_referencers; /*依赖该关系的Relids rels that reference me laterally */
List *indexlist; /* 该关系的IndexOptInfo链表 list of IndexOptInfo */
List *statlist; /* 统计信息链表 list of StatisticExtInfo */
BlockNumber pages; /* 块数 size estimates derived from pg_class */
double tuples; /* 元组数 */
double allvisfrac; /* ? */
PlannerInfo *subroot; /* 如为子查询,存储子查询的root if subquery */
List *subplan_params; /* 如为子查询,存储子查询的参数 if subquery */
int rel_parallel_workers; /* 并行执行,需要多少个workers? wanted number of parallel workers */
/* Information about foreign tables and foreign joins */
//FWD相关信息
Oid serverid; /* identifies server for the table or join */
Oid userid; /* identifies user to check access as */
bool useridiscurrent; /* join is only valid for current user */
/* use "struct FdwRoutine" to avoid including fdwapi.h here */
struct FdwRoutine *fdwroutine;
void *fdw_private;
/* cache space for remembering if we have proven this relation unique */
//已知的,可保证唯一的Relids链表
List *unique_for_rels; /* known unique for these other relid
* set(s) */
List *non_unique_for_rels; /* 已知的,不唯一的Relids链表 known not unique for these set(s) */
/* used by various scans and joins: */
List *baserestrictinfo; /* 如为基本关系,存储约束条件 RestrictInfo structures (if base rel) */
QualCost baserestrictcost; /* 解析约束表达式的成本? cost of evaluating the above */
Index baserestrict_min_security; /* 最低安全等级 min security_level found in
* baserestrictinfo */
List *joininfo; /* 连接语句的约束条件信息 RestrictInfo structures for join clauses
* involving this rel */
bool has_eclass_joins; /* 是否存在等价类连接? T means joininfo is incomplete */
/* used by partitionwise joins: */
bool consider_partitionwise_join; /* 分区? consider partitionwise
* join paths? (if
* partitioned rel) */
Relids top_parent_relids; /* Relids of topmost parents (if "other"
* rel) */
/* used for partitioned relations */
//分区表使用
PartitionScheme part_scheme; /* 分区的schema Partitioning scheme. */
int nparts; /* 分区数 number of partitions */
struct PartitionBoundInfoData *boundinfo; /* 分区边界信息 Partition bounds */
List *partition_qual; /* 分区约束 partition constraint */
struct RelOptInfo **part_rels; /* 分区的RelOptInfo数组 Array of RelOptInfos of partitions,
* stored in the same order of bounds */
List **partexprs; /* 非空分区键表达式 Non-nullable partition key expressions. */
List **nullable_partexprs; /* 可为空的分区键表达式 Nullable partition key expressions. */
List *partitioned_child_rels; /* RT Indexes链表 List of RT indexes. */
} RelOptInfo;
二、源码解读
reconsider_outer_join_clauses函数
该函数遍历优化器信息(PlannerInfo)中的外连接子句(left_join_clauses),把条件分发到合适的地方,其中限制条件(Where子句中的条件)分发到RelOptInfo->baserestrictinfo中,连接条件(连接语句中的条件ON XX)分发到joininfo中
/*
* reconsider_outer_join_clauses
* Re-examine any outer-join clauses that were set aside by
* distribute_qual_to_rels(), and see if we can derive any
* EquivalenceClasses from them. Then, if they were not made
* redundant, push them out into the regular join-clause lists.
*
* When we have mergejoinable clauses A = B that are outer-join clauses,
* we can't blindly combine them with other clauses A = C to deduce B = C,
* since in fact the "equality" A = B won't necessarily hold above the
* outer join (one of the variables might be NULL instead). Nonetheless
* there are cases where we can add qual clauses using transitivity.
*
* One case that we look for here is an outer-join clause OUTERVAR = INNERVAR
* for which there is also an equivalence clause OUTERVAR = CONSTANT.
* It is safe and useful to push a clause INNERVAR = CONSTANT into the
* evaluation of the inner (nullable) relation, because any inner rows not
* meeting this condition will not contribute to the outer-join result anyway.
* (Any outer rows they could join to will be eliminated by the pushed-down
* equivalence clause.)
*
* Note that the above rule does not work for full outer joins; nor is it
* very interesting to consider cases where the generated equivalence clause
* would involve relations outside the outer join, since such clauses couldn't
* be pushed into the inner side's scan anyway. So the restriction to
* outervar = pseudoconstant is not really giving up anything.
*
* For full-join cases, we can only do something useful if it's a FULL JOIN
* USING and a merged column has an equivalence MERGEDVAR = CONSTANT.
* By the time it gets here, the merged column will look like
* COALESCE(LEFTVAR, RIGHTVAR)
* and we will have a full-join clause LEFTVAR = RIGHTVAR that we can match
* the COALESCE expression to. In this situation we can push LEFTVAR = CONSTANT
* and RIGHTVAR = CONSTANT into the input relations, since any rows not
* meeting these conditions cannot contribute to the join result.
*
* Again, there isn't any traction to be gained by trying to deal with
* clauses comparing a mergedvar to a non-pseudoconstant. So we can make
* use of the EquivalenceClasses to search for matching variables that were
* equivalenced to constants. The interesting outer-join clauses were
* accumulated for us by distribute_qual_to_rels.
*
* When we find one of these cases, we implement the changes we want by
* generating a new equivalence clause INNERVAR = CONSTANT (or LEFTVAR, etc)
* and pushing it into the EquivalenceClass structures. This is because we
* may already know that INNERVAR is equivalenced to some other var(s), and
* we'd like the constant to propagate to them too. Note that it would be
* unsafe to merge any existing EC for INNERVAR with the OUTERVAR's EC ---
* that could result in propagating constant restrictions from
* INNERVAR to OUTERVAR, which would be very wrong.
*
* It's possible that the INNERVAR is also an OUTERVAR for some other
* outer-join clause, in which case the process can be repeated. So we repeat
* looping over the lists of clauses until no further deductions can be made.
* Whenever we do make a deduction, we remove the generating clause from the
* lists, since we don't want to make the same deduction twice.
*
* If we don't find any match for a set-aside outer join clause, we must
* throw it back into the regular joinclause processing by passing it to
* distribute_restrictinfo_to_rels(). If we do generate a derived clause,
* however, the outer-join clause is redundant. We still throw it back,
* because otherwise the join will be seen as a clauseless join and avoided
* during join order searching; but we mark it as redundant to keep from
* messing up the joinrel's size estimate. (This behavior means that the
* API for this routine is uselessly complex: we could have just put all
* the clauses into the regular processing initially. We keep it because
* someday we might want to do something else, such as inserting "dummy"
* joinclauses instead of real ones.)
*
* Outer join clauses that are marked outerjoin_delayed are special: this
* condition means that one or both VARs might go to null due to a lower
* outer join. We can still push a constant through the clause, but only
* if its operator is strict; and we *have to* throw the clause back into
* regular joinclause processing. By keeping the strict join clause,
* we ensure that any null-extended rows that are mistakenly generated due
* to suppressing rows not matching the constant will be rejected at the
* upper outer join. (This doesn't work for full-join clauses.)
*/
void
reconsider_outer_join_clauses(PlannerInfo *root)
{
bool found;
ListCell *cell;
ListCell *prev;
ListCell *next;
/* Outer loop repeats until we find no more deductions */
do
{
found = false;
/* Process the LEFT JOIN clauses */
prev = NULL;
for (cell = list_head(root->left_join_clauses); cell; cell = next)//遍历left_join_clauses
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
next = lnext(cell);
if (reconsider_outer_join_clause(root, rinfo, true))
{
found = true;
/* remove it from the list */
root->left_join_clauses =
list_delete_cell(root->left_join_clauses, cell, prev);//如可以,则去掉连接条件(移到约束条件中)
/* we throw it back anyway (see notes above) */
/* but the thrown-back clause has no extra selectivity */
rinfo->norm_selec = 2.0;
rinfo->outer_selec = 1.0;
distribute_restrictinfo_to_rels(root, rinfo);//分发到RelOptInfo中
}
else
prev = cell;
}
/* Process the RIGHT JOIN clauses */
prev = NULL;
for (cell = list_head(root->right_join_clauses); cell; cell = next)//处理右连接
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
next = lnext(cell);
if (reconsider_outer_join_clause(root, rinfo, false))
{
found = true;
/* remove it from the list */
root->right_join_clauses =
list_delete_cell(root->right_join_clauses, cell, prev);
/* we throw it back anyway (see notes above) */
/* but the thrown-back clause has no extra selectivity */
rinfo->norm_selec = 2.0;
rinfo->outer_selec = 1.0;
distribute_restrictinfo_to_rels(root, rinfo);
}
else
prev = cell;
}
/* Process the FULL JOIN clauses */
prev = NULL;
for (cell = list_head(root->full_join_clauses); cell; cell = next)//全连接
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
next = lnext(cell);
if (reconsider_full_join_clause(root, rinfo))
{
found = true;
/* remove it from the list */
root->full_join_clauses =
list_delete_cell(root->full_join_clauses, cell, prev);
/* we throw it back anyway (see notes above) */
/* but the thrown-back clause has no extra selectivity */
rinfo->norm_selec = 2.0;
rinfo->outer_selec = 1.0;
distribute_restrictinfo_to_rels(root, rinfo);
}
else
prev = cell;
}
} while (found);
//处理连接条件链表中余下的条件
/* Now, any remaining clauses have to be thrown back */
foreach(cell, root->left_join_clauses)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
distribute_restrictinfo_to_rels(root, rinfo);
}
foreach(cell, root->right_join_clauses)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
distribute_restrictinfo_to_rels(root, rinfo);
}
foreach(cell, root->full_join_clauses)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
distribute_restrictinfo_to_rels(root, rinfo);
}
}
/*
* reconsider_outer_join_clauses for a single LEFT/RIGHT JOIN clause
*
* Returns true if we were able to propagate a constant through the clause.
*/
static bool
reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
bool outer_on_left)
{
Expr *outervar,
*innervar;
Oid opno,
collation,
left_type,
right_type,
inner_datatype;
Relids inner_relids,
inner_nullable_relids;
ListCell *lc1;
Assert(is_opclause(rinfo->clause));
opno = ((OpExpr *) rinfo->clause)->opno;
collation = ((OpExpr *) rinfo->clause)->inputcollid;
/* If clause is outerjoin_delayed, operator must be strict */
if (rinfo->outerjoin_delayed && !op_strict(opno))
return false;
/* Extract needed info from the clause */
op_input_types(opno, &left_type, &right_type);
if (outer_on_left)
{
outervar = (Expr *) get_leftop(rinfo->clause);
innervar = (Expr *) get_rightop(rinfo->clause);
inner_datatype = right_type;
inner_relids = rinfo->right_relids;
}
else
{
outervar = (Expr *) get_rightop(rinfo->clause);
innervar = (Expr *) get_leftop(rinfo->clause);
inner_datatype = left_type;
inner_relids = rinfo->left_relids;
}
inner_nullable_relids = bms_intersect(inner_relids,
rinfo->nullable_relids);
/* Scan EquivalenceClasses for a match to outervar */
foreach(lc1, root->eq_classes)//遍历等价类
{
EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
bool match;
ListCell *lc2;
/* Ignore EC unless it contains pseudoconstants */
if (!cur_ec->ec_has_const)
continue;
/* Never match to a volatile EC */
if (cur_ec->ec_has_volatile)
continue;
/* It has to match the outer-join clause as to semantics, too */
if (collation != cur_ec->ec_collation)
continue;
if (!equal(rinfo->mergeopfamilies, cur_ec->ec_opfamilies))
continue;
/* Does it contain a match to outervar? */
match = false;
foreach(lc2, cur_ec->ec_members)
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
Assert(!cur_em->em_is_child); /* no children yet */
if (equal(outervar, cur_em->em_expr))
{
match = true;
break;
}
}
if (!match)
continue; /* no match, so ignore this EC */
/*
* Yes it does! Try to generate a clause INNERVAR = CONSTANT for each
* CONSTANT in the EC. Note that we must succeed with at least one
* constant before we can decide to throw away the outer-join clause.
*/
match = false;
foreach(lc2, cur_ec->ec_members)
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
Oid eq_op;
RestrictInfo *newrinfo;
if (!cur_em->em_is_const)
continue; /* ignore non-const members */
eq_op = select_equality_operator(cur_ec,
inner_datatype,
cur_em->em_datatype);
if (!OidIsValid(eq_op))
continue; /* can't generate equality */
newrinfo = build_implied_join_equality(eq_op,
cur_ec->ec_collation,
innervar,
cur_em->em_expr,
bms_copy(inner_relids),
bms_copy(inner_nullable_relids),
cur_ec->ec_min_security);
if (process_equivalence(root, &newrinfo, true))
match = true;
}
/*
* If we were able to equate INNERVAR to any constant, report success.
* Otherwise, fall out of the search loop, since we know the OUTERVAR
* appears in at most one EC.
*/
if (match)
return true;
else
break;
}
return false; /* failed to make any deduction */
}
generate_base_implied_equalities函数
该函数遍历所有的等价类,找出一个隐含的条件然后分发到RelOptInfo中,这样做的目的是为了在连接(join)前过滤元组,减少参与运算的元组数量.
/*
* generate_base_implied_equalities
* Generate any restriction clauses that we can deduce from equivalence
* classes.
*
* When an EC contains pseudoconstants, our strategy is to generate
* "member = const1" clauses where const1 is the first constant member, for
* every other member (including other constants). If we are able to do this
* then we don't need any "var = var" comparisons because we've successfully
* constrained all the vars at their points of creation. If we fail to
* generate any of these clauses due to lack of cross-type operators, we fall
* back to the "ec_broken" strategy described below. (XXX if there are
* multiple constants of different types, it's possible that we might succeed
* in forming all the required clauses if we started from a different const
* member; but this seems a sufficiently hokey corner case to not be worth
* spending lots of cycles on.)
*
* For ECs that contain no pseudoconstants, we generate derived clauses
* "member1 = member2" for each pair of members belonging to the same base
* relation (actually, if there are more than two for the same base relation,
* we only need enough clauses to link each to each other). This provides
* the base case for the recursion: each row emitted by a base relation scan
* will constrain all computable members of the EC to be equal. As each
* join path is formed, we'll add additional derived clauses on-the-fly
* to maintain this invariant (see generate_join_implied_equalities).
*
* If the opfamilies used by the EC do not provide complete sets of cross-type
* equality operators, it is possible that we will fail to generate a clause
* that must be generated to maintain the invariant. (An example: given
* "WHERE a.x = b.y AND b.y = a.z", the scheme breaks down if we cannot
* generate "a.x = a.z" as a restriction clause for A.) In this case we mark
* the EC "ec_broken" and fall back to regurgitating its original source
* RestrictInfos at appropriate times. We do not try to retract any derived
* clauses already generated from the broken EC, so the resulting plan could
* be poor due to bad selectivity estimates caused by redundant clauses. But
* the correct solution to that is to fix the opfamilies ...
*
* Equality clauses derived by this function are passed off to
* process_implied_equality (in plan/initsplan.c) to be inserted into the
* restrictinfo datastructures. Note that this must be called after initial
* scanning of the quals and before Path construction begins.
*
* We make no attempt to avoid generating duplicate RestrictInfos here: we
* don't search ec_sources for matches, nor put the created RestrictInfos
* into ec_derives. Doing so would require some slightly ugly changes in
* initsplan.c's API, and there's no real advantage, because the clauses
* generated here can't duplicate anything we will generate for joins anyway.
*/
void
generate_base_implied_equalities(PlannerInfo *root)
{
ListCell *lc;
Index rti;
foreach(lc, root->eq_classes)//遍历等价类
{
EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc);
Assert(ec->ec_merged == NULL); /* else shouldn't be in list */
Assert(!ec->ec_broken); /* not yet anyway... */
/* Single-member ECs won't generate any deductions */
if (list_length(ec->ec_members) <= 1)//小于1个成员,无需处理类
continue;
if (ec->ec_has_const)//有常量
generate_base_implied_equalities_const(root, ec);
else//无常量
generate_base_implied_equalities_no_const(root, ec);
/* Recover if we failed to generate required derived clauses */
if (ec->ec_broken)//处理失败个案
generate_base_implied_equalities_broken(root, ec);
}
/*
* This is also a handy place to mark base rels (which should all exist by
* now) with flags showing whether they have pending eclass joins.
*/
for (rti = 1; rti < root->simple_rel_array_size; rti++)//设置标记
{
RelOptInfo *brel = root->simple_rel_array[rti];
if (brel == NULL)
continue;
brel->has_eclass_joins = has_relevant_eclass_joinclause(root, brel);
}
}
/*
* generate_base_implied_equalities when EC contains pseudoconstant(s)
*/
static void
generate_base_implied_equalities_const(PlannerInfo *root,
EquivalenceClass *ec)
{
EquivalenceMember *const_em = NULL;
ListCell *lc;
/*
* In the trivial case where we just had one "var = const" clause, push
* the original clause back into the main planner machinery. There is
* nothing to be gained by doing it differently, and we save the effort to
* re-build and re-analyze an equality clause that will be exactly
* equivalent to the old one.
*/
if (list_length(ec->ec_members) == 2 &&
list_length(ec->ec_sources) == 1)
{
RestrictInfo *restrictinfo = (RestrictInfo *) linitial(ec->ec_sources);
if (bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
{
distribute_restrictinfo_to_rels(root, restrictinfo);
return;
}
}
/*
* Find the constant member to use. We prefer an actual constant to
* pseudo-constants (such as Params), because the constraint exclusion
* machinery might be able to exclude relations on the basis of generated
* "var = const" equalities, but "var = param" won't work for that.
*/
foreach(lc, ec->ec_members)//获取常量Member
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
if (cur_em->em_is_const)
{
const_em = cur_em;
if (IsA(cur_em->em_expr, Const))
break;
}
}
Assert(const_em != NULL);
/* Generate a derived equality against each other member */
foreach(lc, ec->ec_members)
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
Oid eq_op;
Assert(!cur_em->em_is_child); /* no children yet */
if (cur_em == const_em)
continue;
eq_op = select_equality_operator(ec,
cur_em->em_datatype,
const_em->em_datatype);
if (!OidIsValid(eq_op))
{
/* failed... */
ec->ec_broken = true;
break;
}
process_implied_equality(root, eq_op, ec->ec_collation,
cur_em->em_expr, const_em->em_expr,
bms_copy(ec->ec_relids),
bms_union(cur_em->em_nullable_relids,
const_em->em_nullable_relids),
ec->ec_min_security,
ec->ec_below_outer_join,
cur_em->em_is_const);//下推条件
}
}
/*
* generate_base_implied_equalities when EC contains no pseudoconstants
*/
static void
generate_base_implied_equalities_no_const(PlannerInfo *root,
EquivalenceClass *ec)
{
EquivalenceMember **prev_ems;
ListCell *lc;
/*
* We scan the EC members once and track the last-seen member for each
* base relation. When we see another member of the same base relation,
* we generate "prev_mem = cur_mem". This results in the minimum number
* of derived clauses, but it's possible that it will fail when a
* different ordering would succeed. XXX FIXME: use a UNION-FIND
* algorithm similar to the way we build merged ECs. (Use a list-of-lists
* for each rel.)
*/
prev_ems = (EquivalenceMember **)
palloc0(root->simple_rel_array_size * sizeof(EquivalenceMember *));
foreach(lc, ec->ec_members)
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
int relid;
Assert(!cur_em->em_is_child); /* no children yet */
if (!bms_get_singleton_member(cur_em->em_relids, &relid))
continue;
Assert(relid < root->simple_rel_array_size);
if (prev_ems[relid] != NULL)
{
EquivalenceMember *prev_em = prev_ems[relid];
Oid eq_op;
eq_op = select_equality_operator(ec,
prev_em->em_datatype,
cur_em->em_datatype);
if (!OidIsValid(eq_op))
{
/* failed... */
ec->ec_broken = true;
break;
}
process_implied_equality(root, eq_op, ec->ec_collation,
prev_em->em_expr, cur_em->em_expr,
bms_copy(ec->ec_relids),
bms_union(prev_em->em_nullable_relids,
cur_em->em_nullable_relids),
ec->ec_min_security,
ec->ec_below_outer_join,
false);
}
prev_ems[relid] = cur_em;
}
pfree(prev_ems);
/*
* We also have to make sure that all the Vars used in the member clauses
* will be available at any join node we might try to reference them at.
* For the moment we force all the Vars to be available at all join nodes
* for this eclass. Perhaps this could be improved by doing some
* pre-analysis of which members we prefer to join, but it's no worse than
* what happened in the pre-8.3 code.
*/
foreach(lc, ec->ec_members)
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
List *vars = pull_var_clause((Node *) cur_em->em_expr,
PVC_RECURSE_AGGREGATES |
PVC_RECURSE_WINDOWFUNCS |
PVC_INCLUDE_PLACEHOLDERS);
add_vars_to_targetlist(root, vars, ec->ec_relids, false);
list_free(vars);
}
}
/*
* generate_base_implied_equalities cleanup after failure
*
* What we must do here is push any zero- or one-relation source RestrictInfos
* of the EC back into the main restrictinfo datastructures. Multi-relation
* clauses will be regurgitated later by generate_join_implied_equalities().
* (We do it this way to maintain continuity with the case that ec_broken
* becomes set only after we've gone up a join level or two.) However, for
* an EC that contains constants, we can adopt a simpler strategy and just
* throw back all the source RestrictInfos immediately; that works because
* we know that such an EC can't become broken later. (This rule justifies
* ignoring ec_has_const ECs in generate_join_implied_equalities, even when
* they are broken.)
*/
static void
generate_base_implied_equalities_broken(PlannerInfo *root,
EquivalenceClass *ec)
{
ListCell *lc;
foreach(lc, ec->ec_sources)
{
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
if (ec->ec_has_const ||
bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
distribute_restrictinfo_to_rels(root, restrictinfo);
}
}
/*
* process_implied_equality
* Create a restrictinfo item that says "item1 op item2", and push it
* into the appropriate lists. (In practice opno is always a btree
* equality operator.)
*
* "qualscope" is the nominal syntactic level to impute to the restrictinfo.
* This must contain at least all the rels used in the expressions, but it
* is used only to set the qual application level when both exprs are
* variable-free. Otherwise the qual is applied at the lowest join level
* that provides all its variables.
*
* "nullable_relids" is the set of relids used in the expressions that are
* potentially nullable below the expressions. (This has to be supplied by
* caller because this function is used after deconstruct_jointree, so we
* don't have knowledge of where the clause items came from.)
*
* "security_level" is the security level to assign to the new restrictinfo.
*
* "both_const" indicates whether both items are known pseudo-constant;
* in this case it is worth applying eval_const_expressions() in case we
* can produce constant TRUE or constant FALSE. (Otherwise it's not,
* because the expressions went through eval_const_expressions already.)
*
* Note: this function will copy item1 and item2, but it is caller's
* responsibility to make sure that the Relids parameters are fresh copies
* not shared with other uses.
*
* This is currently used only when an EquivalenceClass is found to
* contain pseudoconstants. See path/pathkeys.c for more details.
*/
void
process_implied_equality(PlannerInfo *root,
Oid opno,
Oid collation,
Expr *item1,
Expr *item2,
Relids qualscope,
Relids nullable_relids,
Index security_level,
bool below_outer_join,
bool both_const)
{
Expr *clause;
/*
* Build the new clause. Copy to ensure it shares no substructure with
* original (this is necessary in case there are subselects in there...)
*/
clause = make_opclause(opno,
BOOLOID, /* opresulttype */
false, /* opretset */
copyObject(item1),
copyObject(item2),
InvalidOid,
collation);//构造条件表达式
/* If both constant, try to reduce to a boolean constant. */
if (both_const)//
{
clause = (Expr *) eval_const_expressions(root, (Node *) clause);
/* If we produced const TRUE, just drop the clause */
if (clause && IsA(clause, Const))
{
Const *cclause = (Const *) clause;
Assert(cclause->consttype == BOOLOID);
if (!cclause->constisnull && DatumGetBool(cclause->constvalue))
return;
}
}
/*
* Push the new clause into all the appropriate restrictinfo lists.
*/
distribute_qual_to_rels(root, (Node *) clause,
true, below_outer_join, JOIN_INNER,
security_level,
qualscope, NULL, NULL, nullable_relids,
NULL);//分发条件至RelOptInfo
}
三、跟踪分析
测试脚本:
testdb=# explain verbose select t1.dwbh,t2.grbh testdb-# from t_dwxx t1 left join t_grxx t2 on t1.dwbh = t2.dwbh and t2.dwbh = '1001' testdb-# order by t2.dwbh; QUERY PLAN ----------------------------------------------------------------------------------- Sort (cost=19.16..19.56 rows=160 width=114) Output: t1.dwbh, t2.grbh, t2.dwbh Sort Key: t2.dwbh -> Hash Left Join (cost=1.09..13.30 rows=160 width=114) Output: t1.dwbh, t2.grbh, t2.dwbh Hash Cond: ((t1.dwbh)::text = (t2.dwbh)::text) -> Seq Scan on public.t_dwxx t1 (cost=0.00..11.60 rows=160 width=38) Output: t1.dwmc, t1.dwbh, t1.dwdz -> Hash (cost=1.07..1.07 rows=1 width=76) Output: t2.grbh, t2.dwbh -> Seq Scan on public.t_grxx t2 (cost=0.00..1.07 rows=1 width=76) Output: t2.grbh, t2.dwbh Filter: ((t2.dwbh)::text = '1001'::text) (13 rows)
跟踪分析,启动gdb
(gdb) b planmain.c:161 Breakpoint 1 at 0x76958b: file planmain.c, line 161. (gdb) c Continuing. Breakpoint 1, query_planner (root=0x2c92a88, tlist=0x2c5f048, qp_callback=0x76e906 <standard_qp_callback>, qp_extra=0x7fffed6e9c10) at planmain.c:163 warning: Source file is more recent than executable. 163 reconsider_outer_join_clauses(root);
调用前检查root(PlannerInfo)->simple_rel_array数组的内存结构,可以看到baserestrictinfo和joininfo均为NULL
(gdb) p *root->simple_rel_array[1]
$2 = {type = T_RelOptInfo, reloptkind = RELOPT_BASEREL, relids = 0x2c5fdd0, rows = 0, consider_startup = false,
consider_param_startup = false, consider_parallel = false, reltarget = 0x2c5fde8, pathlist = 0x0, 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 = 1, reltablespace = 0,
rtekind = RTE_RELATION, min_attr = -7, max_attr = 3, attr_needed = 0x2c5fe38, attr_widths = 0x2c5fec8,
lateral_vars = 0x0, lateral_referencers = 0x0, indexlist = 0x2c60160, statlist = 0x0, pages = 10, tuples = 160,
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,
partition_qual = 0x0, part_rels = 0x0, partexprs = 0x0, nullable_partexprs = 0x0, partitioned_child_rels = 0x0}
(gdb) p *root->simple_rel_array[2]
$3 = {type = T_RelOptInfo, reloptkind = RELOPT_BASEREL, relids = 0x2c60860, rows = 0, consider_startup = false,
consider_param_startup = false, consider_parallel = false, reltarget = 0x2c60878, pathlist = 0x0, 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 = 2, reltablespace = 0,
rtekind = RTE_RELATION, min_attr = -7, max_attr = 5, attr_needed = 0x2c608c8, attr_widths = 0x2c60958,
lateral_vars = 0x0, lateral_referencers = 0x0, indexlist = 0x0, statlist = 0x0, pages = 1, tuples = 6, 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, partition_qual = 0x0,
part_rels = 0x0, partexprs = 0x0, nullable_partexprs = 0x0, partitioned_child_rels = 0x0}
(gdb)
调用reconsider_outer_join_clauses,注意joininfo,填入了相应的数据
(gdb) p *root->simple_rel_array[1]
$4 = {type = T_RelOptInfo, reloptkind = RELOPT_BASEREL, relids = 0x2c5fdd0, rows = 0, consider_startup = false,
consider_param_startup = false, consider_parallel = false, reltarget = 0x2c5fde8, pathlist = 0x0, 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 = 1, reltablespace = 0,
rtekind = RTE_RELATION, min_attr = -7, max_attr = 3, attr_needed = 0x2c5fe38, attr_widths = 0x2c5fec8,
lateral_vars = 0x0, lateral_referencers = 0x0, indexlist = 0x2c60160, statlist = 0x0, pages = 10, tuples = 160,
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 = 0x2c61780, has_eclass_joins = false, 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) p *root->simple_rel_array[2]
$5 = {type = T_RelOptInfo, reloptkind = RELOPT_BASEREL, relids = 0x2c60860, rows = 0, consider_startup = false,
consider_param_startup = false, consider_parallel = false, reltarget = 0x2c60878, pathlist = 0x0, 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 = 2, reltablespace = 0,
rtekind = RTE_RELATION, min_attr = -7, max_attr = 5, attr_needed = 0x2c608c8, attr_widths = 0x2c60958,
lateral_vars = 0x0, lateral_referencers = 0x0, indexlist = 0x0, statlist = 0x0, pages = 1, tuples = 6, 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 = 0x2c617d0,
has_eclass_joins = false, 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}
调用generate_base_implied_equalities,注意root->simple_rel_array[2]->baserestrictinfo,条件已下推至限制条件(原为连接条件)
(gdb) p *root->simple_rel_array[2]
$7 = {type = T_RelOptInfo, reloptkind = RELOPT_BASEREL, relids = 0x2c60860, rows = 0, consider_startup = false,
consider_param_startup = false, consider_parallel = false, reltarget = 0x2c60878, pathlist = 0x0, 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 = 2, reltablespace = 0,
rtekind = RTE_RELATION, min_attr = -7, max_attr = 5, attr_needed = 0x2c608c8, attr_widths = 0x2c60958,
lateral_vars = 0x0, lateral_referencers = 0x0, indexlist = 0x0, statlist = 0x0, pages = 1, tuples = 6, 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 = 0x2c61820,
baserestrictcost = {startup = 0, per_tuple = 0}, baserestrict_min_security = 0, joininfo = 0x2c617d0,
has_eclass_joins = false, 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}
“PostgreSQL中函数reconsider_outer_join_clauses的主要实现逻辑是什么”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注亿速云网站，小编将为大家输出更多高质量的实用文章！
原创文章，作者：Maggie-Hunter，如若转载，请注明出处：https://blog.ytso.com/tech/database/205257.html