上一小节介绍了函数query_planner中子函数build_base_rel_tlists/find_placeholders_in_jointree/find_lateral_references的实现逻辑,本节介绍deconstruct_jointree函数的主要实现逻辑。
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;
PostponedQual
/* Elements of the postponed_qual_list used during deconstruct_recurse */
typedef struct PostponedQual
{
Node *qual; /* 待处理的表达式,a qual clause waiting to be processed */
Relids relids; /* 该表达式依赖的baserel 集合,the set of baserels it references */
} PostponedQual;
二、源码解读
deconstruct_jointree函数:
/*
****************************************** deconstruct_jointree *********************
递归搜索查询树中jointree中的WHERE/JOIN/ON表达式,
把它们加入到相应的base RelOptInfos的约束条件和连接条件链表中
同时,对于外连接,添加SpecialJoinInfo节点到root->join_info_list中
返回joinlist数据结构,要求函数make_one_rel确定连接顺序
其中:
joinlist是元素为RTR或者sub-joinlist的链表
*/
/*
* deconstruct_jointree
* Recursively scan the query's join tree for WHERE and JOIN/ON qual
* clauses, and add these to the appropriate restrictinfo and joininfo
* lists belonging to base RelOptInfos. Also, add SpecialJoinInfo nodes
* to root->join_info_list for any outer joins appearing in the query tree.
* Return a "joinlist" data structure showing the join order decisions
* that need to be made by make_one_rel().
*
* The "joinlist" result is a list of items that are either RangeTblRef
* jointree nodes or sub-joinlists. All the items at the same level of
* joinlist must be joined in an order to be determined by make_one_rel()
* (note that legal orders may be constrained by SpecialJoinInfo nodes).
* A sub-joinlist represents a subproblem to be planned separately. Currently
* sub-joinlists arise only from FULL OUTER JOIN or when collapsing of
* subproblems is stopped by join_collapse_limit or from_collapse_limit.
*
* NOTE: when dealing with inner joins, it is appropriate to let a qual clause
* be evaluated at the lowest level where all the variables it mentions are
* available. However, we cannot push a qual down into the nullable side(s)
* of an outer join since the qual might eliminate matching rows and cause a
* NULL row to be incorrectly emitted by the join. Therefore, we artificially
* OR the minimum-relids of such an outer join into the required_relids of
* clauses appearing above it. This forces those clauses to be delayed until
* application of the outer join (or maybe even higher in the join tree).
*/
List *
deconstruct_jointree(PlannerInfo *root)
{
List *result;
Relids qualscope;
Relids inner_join_rels;
List *postponed_qual_list = NIL;
/* Start recursion at top of jointree */
Assert(root->parse->jointree != NULL &&
IsA(root->parse->jointree, FromExpr));
/* this is filled as we scan the jointree */
root->nullable_baserels = NULL;
result = deconstruct_recurse(root, (Node *) root->parse->jointree, false,
&qualscope, &inner_join_rels,
&postponed_qual_list);
/* Shouldn't be any leftover quals */
Assert(postponed_qual_list == NIL);
return result;
}
/*
* deconstruct_recurse
* One recursion level of deconstruct_jointree processing.
*
* Inputs:输入
* jtnode is the jointree node to examine
* 待处理的jointree
* below_outer_join is true if this node is within the nullable side of a
* higher-level outer join,在高层外连接的nullable端
*
* Outputs:输出
* *qualscope gets the set of base Relids syntactically included in this
* jointree node (do not modify or free this, as it may also be pointed
* to by RestrictInfo and SpecialJoinInfo nodes)
* jointree节点中base Relids的集合
*
* *inner_join_rels gets the set of base Relids syntactically included in
* inner joins appearing at or below this jointree node (do not modify
* or free this, either)
* 内连接jointree节点或该节点中的base Relids集合
*
* *postponed_qual_list is a list of PostponedQual structs, which we can
* add quals to if they turn out to belong to a higher join level
* PostponedQual结构体链表,如果表达式属于更高层次的连接,可以在其中添加此表达式
*
* Return value is the appropriate joinlist for this jointree node
* 返回值为该jointree节点相应的joinlist
*
* In addition, entries will be added to root->join_info_list for outer joins.
*/
static List *
deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
Relids *qualscope, Relids *inner_join_rels,
List **postponed_qual_list)
{
List *joinlist;
if (jtnode == NULL)
{
*qualscope = NULL;
*inner_join_rels = NULL;
return NIL;
}
if (IsA(jtnode, RangeTblRef))//RTR
{
int varno = ((RangeTblRef *) jtnode)->rtindex;
/* qualscope is just the one RTE */
*qualscope = bms_make_singleton(varno);//添加到qualscope中
/* Deal with any securityQuals attached to the RTE */
if (root->qual_security_level > 0)
process_security_barrier_quals(root,
varno,
*qualscope,
below_outer_join);
/* A single baserel does not create an inner join */
*inner_join_rels = NULL;//inner_join_rels设置为NULL
joinlist = list_make1(jtnode);//添加到joinlist中
}
else if (IsA(jtnode, FromExpr))//FromExpr
{
FromExpr *f = (FromExpr *) jtnode;
List *child_postponed_quals = NIL;
int remaining;
ListCell *l;
/*
* First, recurse to handle child joins. We collapse subproblems into
* a single joinlist whenever the resulting joinlist wouldn't exceed
* from_collapse_limit members. Also, always collapse one-element
* subproblems, since that won't lengthen the joinlist anyway.
*/
*qualscope = NULL;
*inner_join_rels = NULL;//初始化
joinlist = NIL;//初始化
remaining = list_length(f->fromlist);
foreach(l, f->fromlist)
{
Relids sub_qualscope;
List *sub_joinlist;
int sub_members;
sub_joinlist = deconstruct_recurse(root, lfirst(l),
below_outer_join,
&sub_qualscope,
inner_join_rels,
&child_postponed_quals);//递归调用
*qualscope = bms_add_members(*qualscope, sub_qualscope);//添加到qualscope中
sub_members = list_length(sub_joinlist);//sub-joinlist中的元素个数
remaining--;//计数
if (sub_members <= 1 ||
list_length(joinlist) + sub_members + remaining <= from_collapse_limit)
joinlist = list_concat(joinlist, sub_joinlist);//
else
joinlist = lappend(joinlist, sub_joinlist);//
}
/*
* A FROM with more than one list element is an inner join subsuming
* all below it, so we should report inner_join_rels = qualscope. If
* there was exactly one element, we should (and already did) report
* whatever its inner_join_rels were. If there were no elements (is
* that possible?) the initialization before the loop fixed it.
*/
if (list_length(f->fromlist) > 1)
*inner_join_rels = *qualscope;//JOIN
/*
* Try to process any quals postponed by children. If they need
* further postponement, add them to my output postponed_qual_list.
*/
foreach(l, child_postponed_quals)
{
PostponedQual *pq = (PostponedQual *) lfirst(l);
if (bms_is_subset(pq->relids, *qualscope))//pq依赖的relids是qualscope的子集
distribute_qual_to_rels(root, pq->qual,
false, below_outer_join, JOIN_INNER,
root->qual_security_level,
*qualscope, NULL, NULL, NULL,
NULL);//可以分发到Rels中,构建约束条件等
else
*postponed_qual_list = lappend(*postponed_qual_list, pq);//添加到postponed_qual_list链表
}
/*
* Now process the top-level quals.
*/
foreach(l, (List *) f->quals)//处理表达式
{
Node *qual = (Node *) lfirst(l);
distribute_qual_to_rels(root, qual,
false, below_outer_join, JOIN_INNER,
root->qual_security_level,
*qualscope, NULL, NULL, NULL,
postponed_qual_list);//分发到Rels中,构建约束条件等
}
}
else if (IsA(jtnode, JoinExpr))//JoinExpr
{
JoinExpr *j = (JoinExpr *) jtnode;
List *child_postponed_quals = NIL;
Relids leftids,
rightids,
left_inners,
right_inners,
nonnullable_rels,
nullable_rels,
ojscope;
List *leftjoinlist,
*rightjoinlist;
List *my_quals;
SpecialJoinInfo *sjinfo;//特殊连接信息
ListCell *l;
/*
* Order of operations here is subtle and critical. First we recurse
* to handle sub-JOINs. Their join quals will be placed without
* regard for whether this level is an outer join, which is correct.
* Then we place our own join quals, which are restricted by lower
* outer joins in any case, and are forced to this level if this is an
* outer join and they mention the outer side. Finally, if this is an
* outer join, we create a join_info_list entry for the join. This
* will prevent quals above us in the join tree that use those rels
* from being pushed down below this level. (It's okay for upper
* quals to be pushed down to the outer side, however.)
*/
switch (j->jointype)
{
case JOIN_INNER://内连接
leftjoinlist = deconstruct_recurse(root, j->larg,
below_outer_join,
&leftids, &left_inners,
&child_postponed_quals);//递归调用
rightjoinlist = deconstruct_recurse(root, j->rarg,
below_outer_join,
&rightids, &right_inners,
&child_postponed_quals);
*qualscope = bms_union(leftids, rightids);
*inner_join_rels = *qualscope;
/* Inner join adds no restrictions for quals */
nonnullable_rels = NULL;
/* and it doesn't force anything to null, either */
nullable_rels = NULL;
break;
case JOIN_LEFT:
case JOIN_ANTI://左连接或者反连接
leftjoinlist = deconstruct_recurse(root, j->larg,
below_outer_join,
&leftids, &left_inners,
&child_postponed_quals);
rightjoinlist = deconstruct_recurse(root, j->rarg,
true,
&rightids, &right_inners,
&child_postponed_quals);
*qualscope = bms_union(leftids, rightids);
*inner_join_rels = bms_union(left_inners, right_inners);
nonnullable_rels = leftids;
nullable_rels = rightids;
break;
case JOIN_SEMI://半连接
leftjoinlist = deconstruct_recurse(root, j->larg,
below_outer_join,
&leftids, &left_inners,
&child_postponed_quals);
rightjoinlist = deconstruct_recurse(root, j->rarg,
below_outer_join,
&rightids, &right_inners,
&child_postponed_quals);
*qualscope = bms_union(leftids, rightids);
*inner_join_rels = bms_union(left_inners, right_inners);
/* Semi join adds no restrictions for quals */
nonnullable_rels = NULL;
/*
* Theoretically, a semijoin would null the RHS; but since the
* RHS can't be accessed above the join, this is immaterial
* and we needn't account for it.
*/
nullable_rels = NULL;
break;
case JOIN_FULL://全连接
leftjoinlist = deconstruct_recurse(root, j->larg,
true,
&leftids, &left_inners,
&child_postponed_quals);
rightjoinlist = deconstruct_recurse(root, j->rarg,
true,
&rightids, &right_inners,
&child_postponed_quals);
*qualscope = bms_union(leftids, rightids);
*inner_join_rels = bms_union(left_inners, right_inners);
/* each side is both outer and inner */
nonnullable_rels = *qualscope;
nullable_rels = *qualscope;
break;
default:
/* JOIN_RIGHT was eliminated during reduce_outer_joins() */
elog(ERROR, "unrecognized join type: %d",
(int) j->jointype);
nonnullable_rels = NULL; /* keep compiler quiet */
nullable_rels = NULL;
leftjoinlist = rightjoinlist = NIL;
break;
}
/* Report all rels that will be nulled anywhere in the jointree */
root->nullable_baserels = bms_add_members(root->nullable_baserels,
nullable_rels);//nullable-side rels
/*
* Try to process any quals postponed by children. If they need
* further postponement, add them to my output postponed_qual_list.
* Quals that can be processed now must be included in my_quals, so
* that they'll be handled properly in make_outerjoininfo.
*/
my_quals = NIL;//添加到表达式链表中
foreach(l, child_postponed_quals)
{
PostponedQual *pq = (PostponedQual *) lfirst(l);
if (bms_is_subset(pq->relids, *qualscope))
my_quals = lappend(my_quals, pq->qual);
else
{
/*
* We should not be postponing any quals past an outer join.
* If this Assert fires, pull_up_subqueries() messed up.
*/
Assert(j->jointype == JOIN_INNER);
*postponed_qual_list = lappend(*postponed_qual_list, pq);
}
}
/* list_concat is nondestructive of its second argument */
my_quals = list_concat(my_quals, (List *) j->quals);
/*
* For an OJ, form the SpecialJoinInfo now, because we need the OJ's
* semantic scope (ojscope) to pass to distribute_qual_to_rels. But
* we mustn't add it to join_info_list just yet, because we don't want
* distribute_qual_to_rels to think it is an outer join below us.
*
* Semijoins are a bit of a hybrid: we build a SpecialJoinInfo, but we
* want ojscope = NULL for distribute_qual_to_rels.
*/
if (j->jointype != JOIN_INNER)//非内连接
{
sjinfo = make_outerjoininfo(root,
leftids, rightids,
*inner_join_rels,
j->jointype,
my_quals);//构建特殊连接信息
if (j->jointype == JOIN_SEMI)
ojscope = NULL;//半连接
else
ojscope = bms_union(sjinfo->min_lefthand,
sjinfo->min_righthand);
}
else
{
sjinfo = NULL;//内连接,设置为NULL
ojscope = NULL;
}
/* Process the JOIN's qual clauses */
foreach(l, my_quals)//处理JOIN中的qual表达式
{
Node *qual = (Node *) lfirst(l);
distribute_qual_to_rels(root, qual,
false, below_outer_join, j->jointype,
root->qual_security_level,
*qualscope,
ojscope, nonnullable_rels, NULL,
postponed_qual_list);//处理表达式
}
/* Now we can add the SpecialJoinInfo to join_info_list */
if (sjinfo)//特殊连接信息
{
root->join_info_list = lappend(root->join_info_list, sjinfo);
/* Each time we do that, recheck placeholder eval levels */
update_placeholder_eval_levels(root, sjinfo);
}
/*
* Finally, compute the output joinlist. We fold subproblems together
* except at a FULL JOIN or where join_collapse_limit would be
* exceeded.
*/
if (j->jointype == JOIN_FULL)
{
/* force the join order exactly at this node */
joinlist = list_make1(list_make2(leftjoinlist, rightjoinlist));
}
else if (list_length(leftjoinlist) + list_length(rightjoinlist) <=
join_collapse_limit)
{
/* OK to combine subproblems */
joinlist = list_concat(leftjoinlist, rightjoinlist);
}
else
{
/* can't combine, but needn't force join order above here */
Node *leftpart,
*rightpart;
/* avoid creating useless 1-element sublists */
if (list_length(leftjoinlist) == 1)
leftpart = (Node *) linitial(leftjoinlist);
else
leftpart = (Node *) leftjoinlist;
if (list_length(rightjoinlist) == 1)
rightpart = (Node *) linitial(rightjoinlist);
else
rightpart = (Node *) rightjoinlist;
joinlist = list_make2(leftpart, rightpart);
}
}
else
{
elog(ERROR, "unrecognized node type: %d",
(int) nodeTag(jtnode));
joinlist = NIL; /* keep compiler quiet */
}
return joinlist;
}
/*
* distribute_qual_to_rels
* Add clause information to either the baserestrictinfo or joininfo list
* (depending on whether the clause is a join) of each base relation
* mentioned in the clause. A RestrictInfo node is created and added to
* the appropriate list for each rel. Alternatively, if the clause uses a
* mergejoinable operator and is not delayed by outer-join rules, enter
* the left- and right-side expressions into the query's list of
* EquivalenceClasses. Alternatively, if the clause needs to be treated
* as belonging to a higher join level, just add it to postponed_qual_list.
*
* 为每个base relation的base relsbaserestrictinfo或者joininfo链表(取决于子句是否是连接)中添加相关子句信息;
* RestrictInfo节点创建并添加到每个合适的Rel中;或者如果子句为可合并操作符并且没有被外连接所Delayed,则
* 把左右两侧的表达式放到查询的等价类链表中;
* 或者,如果该子句属于更高的连接级别,只需将其添加到postponed_qual_list中
*
* 'clause': the qual clause to be distributed,待分配的表达式子句
* 'is_deduced': true if the qual came from implied-equality deduction,如果表达式来自于隐含等式推导,则为true
* 'below_outer_join': true if the qual is from a JOIN/ON that is below the
* nullable side of a higher-level outer join 来自高层外连接的nullable端的JOIN/ON条件,则为true
* 'jointype': type of join the qual is from (JOIN_INNER for a WHERE clause),qual来自何种连接类型
* 'security_level': security_level to assign to the qual,安全等级
* 'qualscope': set of baserels the qual's syntactic scope covers,表达式的base rels范围
* 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
* needed to form this join,非外连接->NULL,否则为组成该join的最小baserels集合
* 'outerjoin_nonnullable': NULL if not an outer-join qual, else the set of
* baserels appearing on the outer (nonnullable) side of the join
* (for FULL JOIN this includes both sides of the join, and must in fact
* equal qualscope),非外连接->NULL,否则为出现在nonnullable端的base rels集合
* 'deduced_nullable_relids': if is_deduced is true, the nullable relids to
* impute to the clause; otherwise NULL,推导出来的nullable端的relids,否则为NULL
* 'postponed_qual_list': list of PostponedQual structs, which we can add
* this qual to if it turns out to belong to a higher join level.PostponedQual结构体链表
* Can be NULL if caller knows postponement is impossible.
*
* 'qualscope' identifies what level of JOIN the qual came from syntactically.
* 定义了在语法上表达式来自于哪个层次的JOIN
* 'ojscope' is needed if we decide to force the qual up to the outer-join
* level, which will be ojscope not necessarily qualscope.
* 在我们强制把表达式上推至外连接时所需要的信息
*
* In normal use (when is_deduced is false), at the time this is called,
* root->join_info_list must contain entries for all and only those special
* joins that are syntactically below this qual. But when is_deduced is true,
* we are adding new deduced clauses after completion of deconstruct_jointree,
* so it cannot be assumed that root->join_info_list has anything to do with
* qual placement.
*/
static void
distribute_qual_to_rels(PlannerInfo *root, Node *clause,
bool is_deduced,
bool below_outer_join,
JoinType jointype,
Index security_level,
Relids qualscope,
Relids ojscope,
Relids outerjoin_nonnullable,
Relids deduced_nullable_relids,
List **postponed_qual_list)
{
Relids relids;
bool is_pushed_down;
bool outerjoin_delayed;
bool pseudoconstant = false;
bool maybe_equivalence;
bool maybe_outer_join;
Relids nullable_relids;
RestrictInfo *restrictinfo;
/*
* Retrieve all relids mentioned within the clause.
*/
relids = pull_varnos(clause);//遍历,获取该节点中的所有relids
/*
* In ordinary SQL, a WHERE or JOIN/ON clause can't reference any rels
* that aren't within its syntactic scope; however, if we pulled up a
* LATERAL subquery then we might find such references in quals that have
* been pulled up. We need to treat such quals as belonging to the join
* level that includes every rel they reference. Although we could make
* pull_up_subqueries() place such quals correctly to begin with, it's
* easier to handle it here. When we find a clause that contains Vars
* outside its syntactic scope, we add it to the postponed-quals list, and
* process it once we've recursed back up to the appropriate join level.
*/
if (!bms_is_subset(relids, qualscope))//不是qualscope的子集
{
PostponedQual *pq = (PostponedQual *) palloc(sizeof(PostponedQual));
Assert(root->hasLateralRTEs); /* shouldn't happen otherwise */
Assert(jointype == JOIN_INNER); /* mustn't postpone past outer join */
Assert(!is_deduced); /* shouldn't be deduced, either */
pq->qual = clause;
pq->relids = relids;
*postponed_qual_list = lappend(*postponed_qual_list, pq);//添加到postponed_qual_list中,返回
return;
}
/*
* If it's an outer-join clause, also check that relids is a subset of
* ojscope. (This should not fail if the syntactic scope check passed.)
*/
if (ojscope && !bms_is_subset(relids, ojscope))
elog(ERROR, "JOIN qualification cannot refer to other relations");
/*
* If the clause is variable-free, our normal heuristic for pushing it
* down to just the mentioned rels doesn't work, because there are none.
*
* If the clause is an outer-join clause, we must force it to the OJ's
* semantic level to preserve semantics.
*
* Otherwise, when the clause contains volatile functions, we force it to
* be evaluated at its original syntactic level. This preserves the
* expected semantics.
*
* When the clause contains no volatile functions either, it is actually a
* pseudoconstant clause that will not change value during any one
* execution of the plan, and hence can be used as a one-time qual in a
* gating Result plan node. We put such a clause into the regular
* RestrictInfo lists for the moment, but eventually createplan.c will
* pull it out and make a gating Result node immediately above whatever
* plan node the pseudoconstant clause is assigned to. It's usually best
* to put a gating node as high in the plan tree as possible. If we are
* not below an outer join, we can actually push the pseudoconstant qual
* all the way to the top of the tree. If we are below an outer join, we
* leave the qual at its original syntactic level (we could push it up to
* just below the outer join, but that seems more complex than it's
* worth).
*/
if (bms_is_empty(relids))//空的relids
{
if (ojscope)//外连接
{
/* clause is attached to outer join, eval it there */
relids = bms_copy(ojscope);
/* mustn't use as gating qual, so don't mark pseudoconstant */
}
else//非外连接
{
/* eval at original syntactic level */
relids = bms_copy(qualscope);
if (!contain_volatile_functions(clause))//不存在易变函数
{
/* mark as gating qual */
pseudoconstant = true;
/* tell createplan.c to check for gating quals */
root->hasPseudoConstantQuals = true;
/* if not below outer join, push it to top of tree */
if (!below_outer_join)
{
relids =
get_relids_in_jointree((Node *) root->parse->jointree,
false);
qualscope = bms_copy(relids);
}
}
}
}
/*----------
* Check to see if clause application must be delayed by outer-join
* considerations.
*
* A word about is_pushed_down: we mark the qual as "pushed down" if
* it is (potentially) applicable at a level different from its original
* syntactic level. This flag is used to distinguish OUTER JOIN ON quals
* from other quals pushed down to the same joinrel. The rules are:
* WHERE quals and INNER JOIN quals: is_pushed_down = true.
* Non-degenerate OUTER JOIN quals: is_pushed_down = false.
* Degenerate OUTER JOIN quals: is_pushed_down = true.
* A "degenerate" OUTER JOIN qual is one that doesn't mention the
* non-nullable side, and hence can be pushed down into the nullable side
* without changing the join result. It is correct to treat it as a
* regular filter condition at the level where it is evaluated.
*
* Note: it is not immediately obvious that a simple boolean is enough
* for this: if for some reason we were to attach a degenerate qual to
* its original join level, it would need to be treated as an outer join
* qual there. However, this cannot happen, because all the rels the
* clause mentions must be in the outer join's min_righthand, therefore
* the join it needs must be formed before the outer join; and we always
* attach quals to the lowest level where they can be evaluated. But
* if we were ever to re-introduce a mechanism for delaying evaluation
* of "expensive" quals, this area would need work.
*
* Note: generally, use of is_pushed_down has to go through the macro
* RINFO_IS_PUSHED_DOWN, because that flag alone is not always sufficient
* to tell whether a clause must be treated as pushed-down in context.
* This seems like another reason why it should perhaps be rethought.
*----------
*/
if (is_deduced)//推导出来?
{
/*
* If the qual came from implied-equality deduction, it should not be
* outerjoin-delayed, else deducer blew it. But we can't check this
* because the join_info_list may now contain OJs above where the qual
* belongs. For the same reason, we must rely on caller to supply the
* correct nullable_relids set.
*/
Assert(!ojscope);//非外连接
is_pushed_down = true;//可以被下推
outerjoin_delayed = false;//无需外连接延迟
nullable_relids = deduced_nullable_relids;//nullable端的relids
/* Don't feed it back for more deductions */
maybe_equivalence = false;//不需要反馈更多的推导
maybe_outer_join = false;
}
else if (bms_overlap(relids, outerjoin_nonnullable))//与外连接nonnullable端有交集
{
/*
* The qual is attached to an outer join and mentions (some of the)
* rels on the nonnullable side, so it's not degenerate.
*
* We can't use such a clause to deduce equivalence (the left and
* right sides might be unequal above the join because one of them has
* gone to NULL) ... but we might be able to use it for more limited
* deductions, if it is mergejoinable. So consider adding it to the
* lists of set-aside outer-join clauses.
*/
is_pushed_down = false;//不能被下推
maybe_equivalence = false;
maybe_outer_join = true;//可能是外连接
/* Check to see if must be delayed by lower outer join */
outerjoin_delayed = check_outerjoin_delay(root,
&relids,
&nullable_relids,
false);//检查外连接延迟
/*
* Now force the qual to be evaluated exactly at the level of joining
* corresponding to the outer join. We cannot let it get pushed down
* into the nonnullable side, since then we'd produce no output rows,
* rather than the intended single null-extended row, for any
* nonnullable-side rows failing the qual.
*
* (Do this step after calling check_outerjoin_delay, because that
* trashes relids.)
*/
Assert(ojscope);
relids = ojscope;
Assert(!pseudoconstant);
}
else//常规的情况
{
/*
* Normal qual clause or degenerate outer-join clause. Either way, we
* can mark it as pushed-down.
*/
is_pushed_down = true;//可以下推
/* Check to see if must be delayed by lower outer join */
outerjoin_delayed = check_outerjoin_delay(root,
&relids,
&nullable_relids,
true);//检查是否被下层的外连接所延迟
if (outerjoin_delayed)//需延迟
{
/* Should still be a subset of current scope ... */
Assert(root->hasLateralRTEs || bms_is_subset(relids, qualscope));
Assert(ojscope == NULL || bms_is_subset(relids, ojscope));
/*
* Because application of the qual will be delayed by outer join,
* we mustn't assume its vars are equal everywhere.
*/
maybe_equivalence = false;
/*
* It's possible that this is an IS NULL clause that's redundant
* with a lower antijoin; if so we can just discard it. We need
* not test in any of the other cases, because this will only be
* possible for pushed-down, delayed clauses.
*/
if (check_redundant_nullability_qual(root, clause))
return;
}
else//无需延迟
{
/*
* Qual is not delayed by any lower outer-join restriction, so we
* can consider feeding it to the equivalence machinery. However,
* if it's itself within an outer-join clause, treat it as though
* it appeared below that outer join (note that we can only get
* here when the clause references only nullable-side rels).
*/
maybe_equivalence = true;//可能会出现等价类
if (outerjoin_nonnullable != NULL)
below_outer_join = true;
}
/*
* Since it doesn't mention the LHS, it's certainly not useful as a
* set-aside OJ clause, even if it's in an OJ.
*/
maybe_outer_join = false;//不会是外连接
}
/*
* Build the RestrictInfo node itself.
*/
restrictinfo = make_restrictinfo((Expr *) clause,
is_pushed_down,
outerjoin_delayed,
pseudoconstant,
security_level,
relids,
outerjoin_nonnullable,
nullable_relids);//构造约束条件
/*
* If it's a join clause (either naturally, or because delayed by
* outer-join rules), add vars used in the clause to targetlists of their
* relations, so that they will be emitted by the plan nodes that scan
* those relations (else they won't be available at the join node!).
*
* Note: if the clause gets absorbed into an EquivalenceClass then this
* may be unnecessary, but for now we have to do it to cover the case
* where the EC becomes ec_broken and we end up reinserting the original
* clauses into the plan.
*/
if (bms_membership(relids) == BMS_MULTIPLE)//存在多个relids
{
List *vars = pull_var_clause(clause,
PVC_RECURSE_AGGREGATES |
PVC_RECURSE_WINDOWFUNCS |
PVC_INCLUDE_PLACEHOLDERS);//遍历获取Vars
add_vars_to_targetlist(root, vars, relids, false);//添加到相应的投影列中
list_free(vars);
}
/*
* We check "mergejoinability" of every clause, not only join clauses,
* because we want to know about equivalences between vars of the same
* relation, or between vars and consts.
*/
check_mergejoinable(restrictinfo);//检查是否可以合并
/*
* If it is a true equivalence clause, send it to the EquivalenceClass
* machinery. We do *not* attach it directly to any restriction or join
* lists. The EC code will propagate it to the appropriate places later.
*
* If the clause has a mergejoinable operator and is not
* outerjoin-delayed, yet isn't an equivalence because it is an outer-join
* clause, the EC code may yet be able to do something with it. We add it
* to appropriate lists for further consideration later. Specifically:
*
* If it is a left or right outer-join qualification that relates the two
* sides of the outer join (no funny business like leftvar1 = leftvar2 +
* rightvar), we add it to root->left_join_clauses or
* root->right_join_clauses according to which side the nonnullable
* variable appears on.
*
* If it is a full outer-join qualification, we add it to
* root->full_join_clauses. (Ideally we'd discard cases that aren't
* leftvar = rightvar, as we do for left/right joins, but this routine
* doesn't have the info needed to do that; and the current usage of the
* full_join_clauses list doesn't require that, so it's not currently
* worth complicating this routine's API to make it possible.)
*
* If none of the above hold, pass it off to
* distribute_restrictinfo_to_rels().
*
* In all cases, it's important to initialize the left_ec and right_ec
* fields of a mergejoinable clause, so that all possibly mergejoinable
* expressions have representations in EquivalenceClasses. If
* process_equivalence is successful, it will take care of that;
* otherwise, we have to call initialize_mergeclause_eclasses to do it.
*/
if (restrictinfo->mergeopfamilies)//可以
{
if (maybe_equivalence)//存在合并的可能
{
if (check_equivalence_delay(root, restrictinfo) &&
process_equivalence(root, &restrictinfo, below_outer_join))
return;
/* EC rejected it, so set left_ec/right_ec the hard way ... */
if (restrictinfo->mergeopfamilies) /* EC might have changed this */
initialize_mergeclause_eclasses(root, restrictinfo);
/* ... and fall through to distribute_restrictinfo_to_rels */
}
else if (maybe_outer_join && restrictinfo->can_join)//可能是外连接而且约束条件can_join?
{
/* we need to set up left_ec/right_ec the hard way */
initialize_mergeclause_eclasses(root, restrictinfo);
/* now see if it should go to any outer-join lists */
if (bms_is_subset(restrictinfo->left_relids,
outerjoin_nonnullable) &&
!bms_overlap(restrictinfo->right_relids,
outerjoin_nonnullable))
{
/* we have outervar = innervar */
root->left_join_clauses = lappend(root->left_join_clauses,
restrictinfo);
return;
}
if (bms_is_subset(restrictinfo->right_relids,
outerjoin_nonnullable) &&
!bms_overlap(restrictinfo->left_relids,
outerjoin_nonnullable))
{
/* we have innervar = outervar */
root->right_join_clauses = lappend(root->right_join_clauses,
restrictinfo);
return;
}
if (jointype == JOIN_FULL)
{
/* FULL JOIN (above tests cannot match in this case) */
root->full_join_clauses = lappend(root->full_join_clauses,
restrictinfo);
return;
}
/* nope, so fall through to distribute_restrictinfo_to_rels */
}
else
{
/* we still need to set up left_ec/right_ec */
initialize_mergeclause_eclasses(root, restrictinfo);//初始化合并语句的等价类
}
}
/* No EC special case applies, so push it into the clause lists */
distribute_restrictinfo_to_rels(root, restrictinfo);//分发到PlannerInfo中的子句中
}
/*
* distribute_restrictinfo_to_rels
* Push a completed RestrictInfo into the proper restriction or join
* clause list(s).
*
* 下推完整的约束条件到合适的约束语句或连接语句链表中
*
* This is the last step of distribute_qual_to_rels() for ordinary qual
* clauses. Clauses that are interesting for equivalence-class processing
* are diverted to the EC machinery, but may ultimately get fed back here.
*/
void
distribute_restrictinfo_to_rels(PlannerInfo *root,
RestrictInfo *restrictinfo)
{
Relids relids = restrictinfo->required_relids;
RelOptInfo *rel;
switch (bms_membership(relids))
{
case BMS_SINGLETON:
/*
* There is only one relation participating in the clause, so it
* is a restriction clause for that relation.
*/
rel = find_base_rel(root, bms_singleton_member(relids));
/* Add clause to rel's restriction list */
rel->baserestrictinfo = lappend(rel->baserestrictinfo,
restrictinfo);
/* Update security level info */
rel->baserestrict_min_security = Min(rel->baserestrict_min_security,
restrictinfo->security_level);
break;
case BMS_MULTIPLE:
/*
* The clause is a join clause, since there is more than one rel
* in its relid set.
*/
/*
* Check for hashjoinable operators. (We don't bother setting the
* hashjoin info except in true join clauses.)
*/
check_hashjoinable(restrictinfo);
/*
* Add clause to the join lists of all the relevant relations.
*/
add_join_clause_to_rels(root, restrictinfo, relids);
break;
default:
/*
* clause references no rels, and therefore we have no place to
* attach it. Shouldn't get here if callers are working properly.
*/
elog(ERROR, "cannot cope with variable-free clause");
break;
}
}
三、跟踪分析
测试脚本:
testdb=# explain verbose select a.*,b.grbh,b.je
testdb-# from t_dwxx a,lateral (select t1.dwbh,t1.grbh,t2.je from t_grxx t1 inner join t_jfxx t2 on t1.dwbh = a.dwbh and t1.grbh = t2.grbh) b
testdb-# where a.dwbh = '1001'
testdb-# order by b.dwbh;
QUERY PLAN
------------------------------------------------------------------------------------
Nested Loop (cost=15.03..36.10 rows=7 width=558)
Output: a.dwmc, a.dwbh, a.dwdz, t1.grbh, t2.je, t1.dwbh
-> Seq Scan on public.t_dwxx a (cost=0.00..1.04 rows=1 width=474)
Output: a.dwmc, a.dwbh, a.dwdz
Filter: ((a.dwbh)::text = '1001'::text)
-> Hash Join (cost=15.03..34.99 rows=7 width=84)
Output: t1.grbh, t1.dwbh, t2.je
Hash Cond: ((t2.grbh)::text = (t1.grbh)::text)
-> Seq Scan on public.t_jfxx t2 (cost=0.00..17.20 rows=720 width=46)
Output: t2.grbh, t2.ny, t2.je
-> Hash (cost=15.00..15.00 rows=2 width=76)
Output: t1.grbh, t1.dwbh
-> Seq Scan on public.t_grxx t1 (cost=0.00..15.00 rows=2 width=76)
Output: t1.grbh, t1.dwbh
Filter: ((t1.dwbh)::text = '1001'::text) -- 谓词下推
(15 rows)
在deconstruct_jointree上设置断点,启动gdb跟踪:
(gdb) b deconstruct_jointree
Breakpoint 1 at 0x7660e3: file initsplan.c, line 718.
(gdb) c
Continuing.
Breakpoint 1, deconstruct_jointree (root=0x1a498f0) at initsplan.c:718
718 List *postponed_qual_list = NIL;
进入函数deconstruct_jointree
718 List *postponed_qual_list = NIL;
(gdb) n
725 root->nullable_baserels = NULL;
(gdb)
#递归调用deconstruct_recurse
727 result = deconstruct_recurse(root, (Node *) root->parse->jointree, false,
(gdb)
进入deconstruct_recurse函数
(gdb) step
deconstruct_recurse (root=0x1a498f0, jtnode=0x1a473e0, below_outer_join=false, qualscope=0x7ffe02efe0a0,
inner_join_rels=0x7ffe02efe098, postponed_qual_list=0x7ffe02efe090) at initsplan.c:765
765 if (jtnode == NULL)
(gdb) p *jtnode
$1 = {type = T_FromExpr}
处理逻辑进入FromExpr节点
...
804 foreach(l, f->fromlist)
(gdb)
#递归调用deconstruct_recurse
810 sub_joinlist = deconstruct_recurse(root, lfirst(l),
(gdb)
#进入deconstruct_recurse
(gdb) step
deconstruct_recurse (root=0x1a498f0, jtnode=0x19bb600, below_outer_join=false, qualscope=0x7ffe02efdfa0,
inner_join_rels=0x7ffe02efe098, postponed_qual_list=0x7ffe02efdfa8) at initsplan.c:765
765 if (jtnode == NULL)
(gdb) p *jtnode
#FromExpr->fromlist->head的类型是FromExpr
$2 = {type = T_RangeTblRef}
...
(gdb) n
#返回joinlist(varno=1)
1094 return joinlist;
...
回到FromExpr处理逻辑
815 *qualscope = bms_add_members(*qualscope, sub_qualscope);
(gdb) p *qualscope
$8 = (Relids) 0x0
(gdb) p *sub_qualscope
$9 = {nwords = 1, words = 0x1a920c4}
(gdb) p *sub_qualscope->words
$10 = 2
...
#循环继续处理FromExpr->fromlist
804 foreach(l, f->fromlist)
...
#FromExpr#1->fromlist.2的类型是FromExpr
(gdb) p *jtnode
$15 = {type = T_FromExpr}
...
第2个FromExpr中的fromlist,第1个元素为JoinExpr
#即:FromExpr#2->fromlist.1的类型是JoinExpr
...
(gdb)
810 sub_joinlist = deconstruct_recurse(root, lfirst(l),
#直接执行,处理JoinExpr,返回结果
#24=8+16(即3/4号rtindex)
(gdb) p sub_qualscope->words[0]
$22 = 24
815 *qualscope = bms_add_members(*qualscope, sub_qualscope);
...
#处理完JoinExpr后
...
843 if (bms_is_subset(pq->relids, *qualscope))
(gdb) p *qualscope->words
$38 = 24
(gdb) p *pq->relids->words
$41 = 10
#不是子集,添加到postponed_qual_list,由上层负责处理
(gdb) n
850 *postponed_qual_list = lappend(*postponed_qual_list, pq);
856 foreach(l, (List *) f->quals)
(gdb)
#第2个FromExpr没有qual,直接返回
1094 return joinlist;
...
回到第1个FromExpr的处理逻辑
(gdb)
815 *qualscope = bms_add_members(*qualscope, sub_qualscope);
(gdb) p *qualscope->words
$42 = 2
(gdb) p *sub_qualscope->words
$44 = 24
(gdb) n
816 sub_members = list_length(sub_joinlist);
#拼入到qualscope中,26=2+8+16(1/3/4号rte)
(gdb) p *qualscope->words
$45 = 26
...
843 if (bms_is_subset(pq->relids, *qualscope))
#这时候10是26的子集,因此可以调用distribute_qual_to_rels了
(gdb) n
844 distribute_qual_to_rels(root, pq->qual,
(gdb) step
distribute_qual_to_rels (root=0x1a498f0, clause=0x1a56ab0, is_deduced=false, below_outer_join=false, jointype=JOIN_INNER,
security_level=0, qualscope=0x1a920d8, ojscope=0x0, outerjoin_nonnullable=0x0, deduced_nullable_relids=0x0,
postponed_qual_list=0x0) at initsplan.c:1656
1656 bool pseudoconstant = false;
#进入distribute_qual_to_rels
#clause是t_dwxx.dwbh = t_grxx.dwbh
...
(gdb) n
构造约束条件
1897 restrictinfo = make_restrictinfo((Expr *) clause,
...
(gdb) p *restrictinfo
$63 = {type = T_RestrictInfo, clause = 0x1a56ab0, is_pushed_down = true, outerjoin_delayed = false, can_join = true,
pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x1a92840, required_relids = 0x1a926e8,
outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x1a92810, right_relids = 0x1a92828, orclause = 0x0,
parent_ec = 0x0, eval_cost = {startup = -1, per_tuple = 0}, norm_selec = -1, outer_selec = -1,
mergeopfamilies = 0x1a92878, left_ec = 0x0, right_ec = 0x0, left_em = 0x0, right_em = 0x0, scansel_cache = 0x0,
outer_is_left = false, hashjoinoperator = 0, left_bucketsize = -1, right_bucketsize = -1, left_mcvfreq = -1,
right_mcvfreq = -1}
(gdb) n
1971 if (check_equivalence_delay(root, restrictinfo) &&
(gdb)
1972 process_equivalence(root, &restrictinfo, below_outer_join))
(gdb)
1971 if (check_equivalence_delay(root, restrictinfo) &&
(gdb)
检查&处理等价类,如OK,则返回
1973 return;
(gdb)
deconstruct_recurse (root=0x1a498f0, jtnode=0x1a473e0, below_outer_join=false, qualscope=0x7ffe02efe0a0,
inner_join_rels=0x7ffe02efe098, postponed_qual_list=0x7ffe02efe090) at initsplan.c:839
839 foreach(l, child_postponed_quals)
(gdb)
856 foreach(l, (List *) f->quals)
#处理第1个FromExpr的quals(即dwbh='1001')
(gdb) n
858 Node *qual = (Node *) lfirst(l);
(gdb)
860 distribute_qual_to_rels(root, qual,
(gdb)
856 foreach(l, (List *) f->quals)
(gdb)
#返回joinlist(3个RTR)
1094 return joinlist;
(gdb) n
1095 }
(gdb)
deconstruct_jointree (root=0x1a498f0) at initsplan.c:734
734 return result;
执行完毕,在PlannerInfo中产生了两个等价类
(gdb) p *root
$85 = {type = T_PlannerInfo, parse = 0x19bb1a0, glob = 0x1a53ee8, query_level = 1, parent_root = 0x0, plan_params = 0x0,
outer_params = 0x0, simple_rel_array = 0x1a90568, simple_rel_array_size = 6, simple_rte_array = 0x1a905b8,
all_baserels = 0x0, nullable_baserels = 0x0, join_rel_list = 0x0, join_rel_hash = 0x0, join_rel_level = 0x0,
join_cur_level = 0, init_plans = 0x0, cte_plan_ids = 0x0, multiexpr_params = 0x0, eq_classes = 0x1a92650,
canon_pathkeys = 0x0, 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 = 0x0, upper_rels = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, upper_targets = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0}, processed_tlist = 0x1a56160, grouping_map = 0x0, minmax_aggs = 0x0, planner_cxt = 0x1997040,
total_table_pages = 0, tuple_fraction = 0, limit_tuples = -1, qual_security_level = 0, inhTargetKind = INHKIND_NONE,
hasJoinRTEs = true, hasLateralRTEs = true, 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}
(gdb) p *root->eq_classes
$86 = {type = T_List, length = 2, head = 0x1a92630, tail = 0x1a92ad0}
(gdb) p *(Node *)root->eq_classes->head->data.ptr_value
$87 = {type = T_EquivalenceClass}
(gdb) p *(EquivalenceClass *)root->eq_classes->head->data.ptr_value
$88 = {type = T_EquivalenceClass, ec_opfamilies = 0x1a92350, ec_collation = 100, ec_members = 0x1a92590,
ec_sources = 0x1a924d8, ec_derives = 0x0, ec_relids = 0x1a92558, ec_has_const = false, ec_has_volatile = false,
ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0}
(gdb) p *(EquivalenceClass *)root->eq_classes->head->next->data.ptr_value
$89 = {type = T_EquivalenceClass, ec_opfamilies = 0x1a92878, ec_collation = 100, ec_members = 0x1a92a30,
ec_sources = 0x1a92978, ec_derives = 0x0, ec_relids = 0x1a929f8, ec_has_const = true, ec_has_volatile = false,
ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0}
(gdb)
第1个等价类有2个Member
(gdb) p *((EquivalenceClass *)root->eq_classes->head->data.ptr_value)->ec_members
$91 = {type = T_List, length = 2, head = 0x1a92570, tail = 0x1a92610}
第2个等价类有3个Member
(gdb) p *((EquivalenceClass *)root->eq_classes->head->next->data.ptr_value)->ec_members
$97 = {type = T_List, length = 3, head = 0x1a92a10, tail = 0x1a92d08}
等价类的解释下节再行介绍.
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