在查询分区表的时候PG如何确定查询的是哪个分区？如何确定？相关的机制是什么？接下来几个章节将一一介绍，本节是第一部分。
零、实现机制
我们先看下面的例子,两个普通表t_normal_1和t_normal_2,执行UNION ALL操作:
drop table if exists t_normal_1;
drop table if exists t_normal_2;
create table t_normal_1 (c1 int not null,c2 varchar(40),c3 varchar(40));
create table t_normal_2 (c1 int not null,c2 varchar(40),c3 varchar(40));
insert into t_normal_1(c1,c2,c3) VALUES(0,'HASH0','HAHS0');
insert into t_normal_2(c1,c2,c3) VALUES(0,'HASH0','HAHS0');
testdb=# explain verbose select * from t_normal_1 where c1 = 0
testdb-# union all
testdb-# select * from t_normal_2 where c1 <> 0;
QUERY PLAN
----------------------------------------------------------------------------
Append (cost=0.00..34.00 rows=350 width=200)
-> Seq Scan on public.t_normal_1 (cost=0.00..14.38 rows=2 width=200)
Output: t_normal_1.c1, t_normal_1.c2, t_normal_1.c3
Filter: (t_normal_1.c1 = 0)
-> Seq Scan on public.t_normal_2 (cost=0.00..14.38 rows=348 width=200)
Output: t_normal_2.c1, t_normal_2.c2, t_normal_2.c3
Filter: (t_normal_2.c1 <> 0)
(7 rows)
两张普通表的UNION ALL,PG使用APPEND操作符把t_normal_1顺序扫描的结果集和t_normal_2顺序扫描的结果集"APPEND"在一起作为最终的结果集输出.
分区表的查询也是类似的机制,把各个分区的结果集APPEND在一起,然后作为最终的结果集输出,如下例所示:
testdb=# explain verbose select * from t_hash_partition where c1 = 1 OR c1 = 2;
QUERY PLAN
-------------------------------------------------------------------------------------
Append (cost=0.00..30.53 rows=6 width=200)
-> Seq Scan on public.t_hash_partition_1 (cost=0.00..15.25 rows=3 width=200)
Output: t_hash_partition_1.c1, t_hash_partition_1.c2, t_hash_partition_1.c3
Filter: ((t_hash_partition_1.c1 = 1) OR (t_hash_partition_1.c1 = 2))
-> Seq Scan on public.t_hash_partition_3 (cost=0.00..15.25 rows=3 width=200)
Output: t_hash_partition_3.c1, t_hash_partition_3.c2, t_hash_partition_3.c3
Filter: ((t_hash_partition_3.c1 = 1) OR (t_hash_partition_3.c1 = 2))
(7 rows)
查询分区表t_hash_partition,条件为c1 = 1 OR c1 = 2,从执行计划可见是把t_hash_partition_1顺序扫描的结果集和t_hash_partition_3顺序扫描的结果集"APPEND"在一起作为最终的结果集输出.
这里面有几个问题需要解决:
1.识别分区表并找到所有的分区子表;
2.根据约束条件识别需要查询的分区,这是出于性能的考虑;
3.对结果集执行APPEND,作为最终结果输出.
本节介绍了PG如何识别分区表并找到所有的分区子表,实现的函数是expand_inherited_tables.
一、数据结构
AppendRelInfo
Append-relation信息.
当我们将可继承表(分区表)或UNION-ALL子查询展开为“追加关系”(本质上是子RTE的链表)时，为每个子RTE构建一个AppendRelInfo。
AppendRelInfos链表指示在展开父节点时必须包含哪些子rte，每个节点具有将引用父节点的Vars转换为引用该子节点的Vars所需的所有信息。
/*
* Append-relation info.
* Append-relation信息.
*
* When we expand an inheritable table or a UNION-ALL subselect into an
* "append relation" (essentially, a list of child RTEs), we build an
* AppendRelInfo for each child RTE. The list of AppendRelInfos indicates
* which child RTEs must be included when expanding the parent, and each node
* carries information needed to translate Vars referencing the parent into
* Vars referencing that child.
* 当我们将可继承表(分区表)或UNION-ALL子查询展开为“追加关系”(本质上是子RTE的链表)时，
* 为每个子RTE构建一个AppendRelInfo。
* AppendRelInfos链表指示在展开父节点时必须包含哪些子rte，
* 每个节点具有将引用父节点的Vars转换为引用该子节点的Vars所需的所有信息。
*
* These structs are kept in the PlannerInfo node's append_rel_list.
* Note that we just throw all the structs into one list, and scan the
* whole list when desiring to expand any one parent. We Could have used
* a more complex data structure (eg, one list per parent), but this would
* be harder to update during operations such as pulling up subqueries,
* and not really any easier to scan. Considering that typical queries
* will not have many different append parents, it doesn't seem worthwhile
* to complicate things.
* 这些结构体保存在PlannerInfo节点的append_rel_list中。
* 注意，只是将所有的结构体放入一个链表中，并在希望展开任何父类时扫描整个链表。
* 本可以使用更复杂的数据结构(例如，每个父节点一个列表)，
* 但是在提取子查询之类的操作中更新它会更困难，
* 而且实际上也不会更容易扫描。
* 考虑到典型的查询不会有很多不同的附加项，因此似乎不值得将事情复杂化。
*
* Note: after completion of the planner prep phase, any given RTE is an
* append parent having entries in append_rel_list if and only if its
* "inh" flag is set. We clear "inh" for plain tables that turn out not
* to have inheritance children, and (in an abuse of the original meaning
* of the flag) we set "inh" for subquery RTEs that turn out to be
* flattenable UNION ALL queries. This lets us avoid useless searches
* of append_rel_list.
* 注意:计划准备阶段完成后,
* 当且仅当它的“inh”标志已设置时,给定的RTE是一个append parent在append_rel_list中的一个条目。
* 我们为没有child的平面表清除“inh”标记,
* 同时(有滥用标记的嫌疑)为UNION ALL查询中的子查询RTEs设置“inh”标记。
* 这样可以避免对append_rel_list进行无用的搜索。
*
* Note: the data structure assumes that append-rel members are single
* baserels. This is OK for inheritance, but it prevents us from pulling
* up a UNION ALL member subquery if it contains a join. While that Could
* be fixed with a more complex data structure, at present there's not much
* point because no improvement in the plan Could result.
* 注意:数据结构假定附加的rel成员是独立的baserels。
* 这对于继承来说是可以的，但是如果UNION ALL member子查询包含一个join，
* 那么它将阻止我们提取UNION ALL member子查询。
* 虽然可以用更复杂的数据结构解决这个问题，但目前没有太大意义，因为该计划可能不会有任何改进。
*/
typedef struct AppendRelInfo
{
NodeTag type;
/*
* These fields uniquely identify this append relationship. There can be
* (in fact, always should be) multiple AppendRelInfos for the same
* parent_relid, but never more than one per child_relid, since a given
* RTE cannot be a child of more than one append parent.
* 这些字段惟一地标识这个append relationship。
* 对于同一个parent_relid可以有(实际上应该总是)多个AppendRelInfos，
* 但是每个child_relid不能有多个AppendRelInfos，
* 因为给定的RTE不能是多个append parent的子节点。
*/
Index parent_relid; /* parent rel的RT索引;RT index of append parent rel */
Index child_relid; /* child rel的RT索引;RT index of append child rel */
/*
* For an inheritance appendrel, the parent and child are both regular
* relations, and we store their rowtype OIDs here for use in translating
* whole-row Vars. For a UNION-ALL appendrel, the parent and child are
* both subqueries with no named rowtype, and we store InvalidOid here.
* 对于继承appendrel，父类和子类都是普通关系，
* 我们将它们的rowtype OIDs存储在这里，用于转换whole-row Vars。
* 对于UNION-ALL appendrel，父查询和子查询都是没有指定行类型的子查询，
* 我们在这里存储InvalidOid。
*/
Oid parent_reltype; /* OID of parent's composite type */
Oid child_reltype; /* OID of child's composite type */
/*
* The N'th element of this list is a Var or expression representing the
* child column corresponding to the N'th column of the parent. This is
* used to translate Vars referencing the parent rel into references to
* the child. A list element is NULL if it corresponds to a dropped
* column of the parent (this is only possible for inheritance cases, not
* UNION ALL). The list elements are always simple Vars for inheritance
* cases, but can be arbitrary expressions in UNION ALL cases.
* 这个列表的第N个元素是一个Var或表达式，表示与父元素的第N列对应的子列。
* 这用于将引用parent rel的Vars转换为对子rel的引用。
* 如果链表元素与父元素的已删除列相对应，则该元素为NULL
* (这只适用于继承情况，而不是UNION ALL)。
* 对于继承情况，链表元素总是简单的变量，但是可以是UNION ALL情况下的任意表达式。
*
* Notice we only store entries for user columns (attno > 0). Whole-row
* Vars are special-cased, and system columns (attno < 0) need no special
* translation since their attnos are the same for all tables.
* 注意，我们只存储用户列的条目(attno > 0)。
* Whole-row Vars是大小写敏感的，系统列(attno < 0)不需要特别的转换，
* 因为它们的attno对所有表都是相同的。
*
* Caution: the Vars have varlevelsup = 0. Be careful to adjust as needed
* when copying into a subquery.
* 注意:Vars的varlevelsup = 0。
* 在将数据复制到子查询时，要注意根据需要进行调整。
*/
//child's Vars中的表达式
List *translated_vars; /* Expressions in the child's Vars */
/*
* We store the parent table's OID here for inheritance, or InvalidOid for
* UNION ALL. This is only needed to help in generating error messages if
* an attempt is made to reference a dropped parent column.
* 我们将父表的OID存储在这里用于继承，
* 如为UNION ALL,则这里存储的是InvalidOid。
* 只有在试图引用已删除的父列时，才需要这样做来帮助生成错误消息。
*/
Oid parent_reloid; /* OID of parent relation */
} AppendRelInfo;
PlannerInfo
该数据结构用于存储查询语句在规划/优化过程中的相关信息
/*----------
* PlannerInfo
* Per-query information for planning/optimization
* 用于规划/优化的每个查询信息
*
* This struct is conventionally called "root" in all the planner routines.
* It holds links to all of the planner's working state, in addition to the
* original Query. Note that at present the planner extensively modifies
* the passed-in Query data structure; someday that should stop.
* 在所有计划程序例程中，这个结构通常称为“root”。
* 除了原始查询之外，它还保存到所有计划器工作状态的链接。
* 注意，目前计划器会毫无节制的修改传入的查询数据结构,相信总有一天这种情况会停止的。
*----------
*/
struct AppendRelInfo;
typedef struct PlannerInfo
{
NodeTag type;//Node标识
//查询树
Query *parse; /* the Query being planned */
//当前的planner全局信息
PlannerGlobal *glob; /* global info for current planner run */
//查询层次,1标识最高层
Index query_level; /* 1 at the outermost Query */
// 如为子计划,则这里存储父计划器指针,NULL标识最高层
struct PlannerInfo *parent_root; /* NULL at outermost Query */
/*
* plan_params contains the expressions that this query level needs to
* make available to a lower query level that is currently being planned.
* outer_params contains the paramIds of ParaM_EXEC Params that outer
* query levels will make available to this query level.
* plan_params包含该查询级别需要提供给当前计划的较低查询级别的表达式。
* outer_params包含ParaM_EXEC Params的参数，外部查询级别将使该查询级别可用这些参数。
*/
List *plan_params; /* list of PlannerParamItems, see below */
Bitmapset *outer_params;
/*
* simple_rel_array holds pointers to "base rels" and "other rels" (see
* comments for RelOptInfo for more info). It is indexed by rangetable
* index (so entry 0 is always wasted). Entries can be NULL when an RTE
* does not correspond to a base relation, such as a join RTE or an
* unreferenced view RTE; or if the RelOptInfo hasn't been made yet.
* simple_rel_array保存指向“base rels”和“other rels”的指针
* (有关RelOptInfo的更多信息，请参见注释)。
* 它由可范围表索引建立索引(因此条目0总是被浪费)。
* 当RTE与基本关系(如JOIN RTE或未被引用的视图RTE时)不相对应
* 或者如果RelOptInfo还没有生成，条目可以为NULL。
*/
//RelOptInfo数组,存储"base rels",比如基表/子查询等.
//该数组与RTE的顺序一一对应,而且是从1开始,因此[0]无用 */
struct RelOptInfo **simple_rel_array; /* All 1-rel RelOptInfos */
int simple_rel_array_size; /* 数组大小,allocated size of array */
/*
* simple_rte_array is the same length as simple_rel_array and holds
* pointers to the associated rangetable entries. This lets us avoid
* rt_fetch(), which can be a bit slow once large inheritance sets have
* been expanded.
* simple_rte_array的长度与simple_rel_array相同，
* 并保存指向相应范围表条目的指针。
* 这使我们可以避免执行rt_fetch()，因为一旦扩展了大型继承集，rt_fetch()可能会有点慢。
*/
//RTE数组
RangeTblEntry **simple_rte_array; /* rangetable as an array */
/*
* append_rel_array is the same length as the above arrays, and holds
* pointers to the corresponding AppendRelInfo entry indexed by
* child_relid, or NULL if none. The array itself is not allocated if
* append_rel_list is empty.
* append_rel_array与上述数组的长度相同，
* 并保存指向对应的AppendRelInfo条目的指针，该条目由child_relid索引，
* 如果没有索引则为NULL。
* 如果append_rel_list为空，则不分配数组本身。
*/
//处理集合操作如UNION ALL时使用和分区表时使用
struct AppendRelInfo **append_rel_array;
/*
* all_baserels is a Relids set of all base relids (but not "other"
* relids) in the query; that is, the Relids identifier of the final join
* we need to form. This is computed in make_one_rel, just before we
* start making Paths.
* all_baserels是查询中所有base relids(但不是“other” relids)的一个Relids集合;
* 也就是说，这是需要形成的最终连接的Relids标识符。
* 这是在开始创建路径之前在make_one_rel中计算的。
*/
Relids all_baserels;//"base rels"
/*
* nullable_baserels is a Relids set of base relids that are nullable by
* some outer join in the jointree; these are rels that are potentially
* nullable below the WHERE clause, SELECT targetlist, etc. This is
* computed in deconstruct_jointree.
* nullable_baserels是由jointree中的某些外连接中值可为空的base Relids集合;
* 这些是在WHERE子句、SELECT targetlist等下面可能为空的树。
* 这是在deconstruct_jointree中处理获得的。
*/
//Nullable-side端的"base rels"
Relids nullable_baserels;
/*
* join_rel_list is a list of all join-relation RelOptInfos we have
* considered in this planning run. For small problems we just scan the
* list to do lookups, but when there are many join relations we build a
* hash table for faster lookups. The hash table is present and valid
* when join_rel_hash is not NULL. Note that we still maintain the list
* even when using the hash table for lookups; this simplifies life for
* GEQO.
* join_rel_list是在计划执行中考虑的所有连接关系RelOptInfos的链表。
* 对于小问题，只需要扫描链表执行查找，但是当存在许多连接关系时，
* 需要构建一个散列表来进行更快的查找。
* 当join_rel_hash不为空时，哈希表是有效可用于查询的。
* 注意，即使在使用哈希表进行查找时，仍然维护该链表;这简化了GEQO(遗传算法)的生命周期。
*/
//参与连接的Relation的RelOptInfo链表
List *join_rel_list; /* list of join-relation RelOptInfos */
//可加快链表访问的hash表
struct HTAB *join_rel_hash; /* optional hashtable for join relations */
/*
* When doing a dynamic-programming-style join search, join_rel_level[k]
* is a list of all join-relation RelOptInfos of level k, and
* join_cur_level is the current level. New join-relation RelOptInfos are
* automatically added to the join_rel_level[join_cur_level] list.
* join_rel_level is NULL if not in use.
* 在执行动态规划算法的连接搜索时，join_rel_level[k]是k级的所有连接关系RelOptInfos的列表，
* join_cur_level是当前级别。
* 新的连接关系RelOptInfos会自动添加到join_rel_level[join_cur_level]链表中。
* 如果不使用join_rel_level，则为NULL。
*/
//RelOptInfo指针链表数组,k层的join存储在[k]中
List **join_rel_level; /* lists of join-relation RelOptInfos */
//当前的join层次
int join_cur_level; /* index of list being extended */
//查询的初始化计划链表
List *init_plans; /* init SubPlans for query */
//CTE子计划ID链表
List *cte_plan_ids; /* per-CTE-item list of subplan IDs */
//MULTIEXPR子查询输出的参数链表的链表
List *multiexpr_params; /* List of Lists of Params for MULTIEXPR
* subquery outputs */
//活动的等价类链表
List *eq_classes; /* list of active EquivalenceClasses */
//规范化的PathKey链表
List *canon_pathkeys; /* list of "canonical" PathKeys */
//外连接约束条件链表(左)
List *left_join_clauses; /* list of RestrictInfos for mergejoinable
* outer join clauses w/nonnullable var on
* left */
//外连接约束条件链表(右)
List *right_join_clauses; /* list of RestrictInfos for mergejoinable
* outer join clauses w/nonnullable var on
* right */
//全连接约束条件链表
List *full_join_clauses; /* list of RestrictInfos for mergejoinable
* full join clauses */
//特殊连接信息链表
List *join_info_list; /* list of SpecialJoinInfos */
//AppendRelInfo链表
List *append_rel_list; /* list of AppendRelInfos */
//PlanRowMarks链表
List *rowMarks; /* list of PlanRowMarks */
//PHI链表
List *placeholder_list; /* list of PlaceHolderInfos */
// 外键信息链表
List *fkey_list; /* list of ForeignKeyOptInfos */
//query_planner()要求的PathKeys链表
List *query_pathkeys; /* desired pathkeys for query_planner() */
//分组子句路径键
List *group_pathkeys; /* groupClause pathkeys, if any */
//窗口函数路径键
List *window_pathkeys; /* pathkeys of bottom window, if any */
//distinctClause路径键
List *distinct_pathkeys; /* distinctClause pathkeys, if any */
//排序路径键
List *sort_pathkeys; /* sortClause pathkeys, if any */
//已规范化的分区Schema
List *part_schemes; /* Canonicalised partition schemes used in the
* query. */
//尝试连接的RelOptInfo链表
List *initial_rels; /* RelOptInfos we are Now trying to join */
/* Use fetch_upper_rel() to get any particular upper rel */
//上层的RelOptInfo链表
List *upper_rels[UPPERREL_FINAL + 1]; /* upper-rel RelOptInfos */
/* Result tlists chosen by grouping_planner for upper-stage processing */
//grouping_planner为上层处理选择的结果tlists
struct PathTarget *upper_targets[UPPERREL_FINAL + 1];//
/*
* grouping_planner passes back its final processed targetlist here, for
* use in relabeling the topmost tlist of the finished Plan.
* grouping_planner在这里传回它最终处理过的targetlist，用于重新标记已完成计划的最顶层tlist。
*/
////最后需处理的投影列
List *processed_tlist;
/* Fields filled during create_plan() for use in setrefs.c */
//setrefs.c中在create_plan()函数调用期间填充的字段
//分组函数属性映射
AttrNumber *grouping_map; /* for GroupingFunc fixup */
//MinMaxAggInfos链表
List *minmax_aggs; /* List of MinMaxAggInfos */
//内存上下文
MemoryContext planner_cxt; /* context holding PlannerInfo */
//关系的page计数
double total_table_pages; /* # of pages in all tables of query */
//query_planner输入参数:元组处理比例
double tuple_fraction; /* tuple_fraction passed to query_planner */
//query_planner输入参数:limit_tuple
double limit_tuples; /* limit_tuples passed to query_planner */
//表达式的最小安全等级
Index qual_security_level; /* minimum security_level for quals */
/* Note: qual_security_level is zero if there are no securityQuals */
//注意:如果没有securityQuals, 则qual_security_level是NULL(0)
//如目标relation是分区表的child/partition/分区表,则通过此字段标记
InheritanceKind inhTargetKind; /* indicates if the target relation is an
* inheritance child or partition or a
* partitioned table */
//是否存在RTE_JOIN的RTE
bool hasJoinRTEs; /* true if any RTEs are RTE_JOIN kind */
//是否存在标记为LAteraL的RTE
bool hasLateralRTEs; /* true if any RTEs are marked LAteraL */
//是否存在已在jointree删除的RTE
bool hasDeletedRTEs; /* true if any RTE was deleted from jointree */
//是否存在Having子句
bool hasHavingQual; /* true if havingQual was non-null */
//如约束条件中存在pseudoconstant = true,则此字段为T
bool hasPseudoConstantQuals; /* true if any RestrictInfo has
* pseudoconstant = true */
//是否存在递归语句
bool hasRecursion; /* true if planning a recursive WITH item */
/* These fields are used only when hasRecursion is true: */
//这些字段仅在hasRecursion为T时使用:
//工作表的ParaM_EXEC ID
int wt_param_id; /* ParaM_EXEC ID for the work table */
//非递归模式的访问路径
struct Path *non_recursive_path; /* a path for non-recursive term */
/* These fields are workspace for createplan.c */
//这些字段用于createplan.c
//当前节点之上的外部rels
Relids curOuterRels; /* outer rels above current node */
//未赋值的nestLoopParams参数
List *curOuterParams; /* not-yet-assigned nestLoopParams */
/* optional private data for join_search_hook, e.g., GEQO */
//可选的join_search_hook私有数据，例如GEQO
void *join_search_private;
/* Does this query modify any partition key columns? */
//该查询是否更新分区键列?
bool partColsUpdated;
} PlannerInfo;
二、源码解读
expand_inherited_tables函数将表示继承集合的每个范围表条目展开为“append relation”。
/*
* expand_inherited_tables
* Expand each rangetable entry that represents an inheritance set
* into an "append relation". At the conclusion of this process,
* the "inh" flag is set in all and only those RTEs that are append
* relation parents.
* 将表示继承集合的每个范围表条目展开为“append relation”。
* 在这个过程结束时，“inh”标志被设置在所有且只有那些作为append
* relation parents的RTEs中。
*/
void
expand_inherited_tables(PlannerInfo *root)
{
Index nrtes;
Index rti;
ListCell *rl;
/*
* expand_inherited_rtentry may add RTEs to parse->rtable. The function is
* expected to recursively handle any RTEs that it creates with inh=true.
* So just scan as far as the original end of the rtable list.
* expand_inherited_rtentry可以添加RTEs到parse->rtable中。
* 这个函数被期望递归地处理它用inh = true创建的所有RTEs。
* 所以只要扫描到rtable链表最开始的末尾即可。
*/
nrtes = list_length(root->parse->rtable);
rl = list_head(root->parse->rtable);
for (rti = 1; rti <= nrtes; rti++)
{
RangeTblEntry *rte = (RangeTblEntry *) lfirst(rl);
expand_inherited_rtentry(root, rte, rti);
rl = lnext(rl);
}
}
/*
* expand_inherited_rtentry
* Check whether a rangetable entry represents an inheritance set.
* If so, add entries for all the child tables to the query's
* rangetable, and build AppendRelInfo nodes for all the child tables
* and add them to root->append_rel_list. If not, clear the entry's
* "inh" flag to prevent later code from looking for AppendRelInfos.
* 检查范围表条目是否表示继承集合。
* 如是，将所有子表的条目添加到查询的范围表中，
* 并为所有子表构建AppendRelInfo节点，并将它们添加到root->append_rel_list。
* 如没有，清除条目的“inh”标志，以防止以后的代码寻找AppendRelInfos。
*
* Note that the original RTE is considered to represent the whole
* inheritance set. The first of the generated RTEs is an RTE for the same
* table, but with inh = false, to represent the parent table in its role
* as a simple member of the inheritance set.
* 注意，原始的RTEs被认为代表了整个继承集合。
* 生成的第一个RTE是同一个表的RTE，但inh = false表示父表作为继承集的一个简单成员的角色。
*
* A childless table is never considered to be an inheritance set. For
* regular inheritance, a parent RTE must always have at least two associated
* AppendRelInfos: one corresponding to the parent table as a simple member of
* inheritance set and one or more corresponding to the actual children.
* Since a partitioned table is not scanned, it might have only one associated
* AppendRelInfo.
* 无子表的关系永远不会被认为是继承集合。
* 对于常规继承，父RTE必须始终至少有两个相关的AppendRelInfos:
* 一个作为继承集的简单成员与父表相对应，
* 另一个或多个与实际的子表相对应。
* 因为没有扫描分区表，所以它可能只有一个关联的AppendRelInfo。
*/
static void
expand_inherited_rtentry(PlannerInfo *root, RangeTblEntry *rte, Index rti)
{
Oid parentOID;
PlanRowMark *oldrc;
Relation oldrelation;
LOCKMODE lockmode;
List *inhOIDs;
ListCell *l;
/* Does RT entry allow inheritance? */
//是否分区表?
if (!rte->inh)
return;
/* Ignore any already-expanded UNION ALL nodes */
//忽略所有已扩展的UNION ALL节点
if (rte->rtekind != RTE_RELATION)
{
Assert(rte->rtekind == RTE_SUBQUERY);
return;//返回
}
/* Fast path for common case of childless table */
//对于常规的无子表的关系,快速判断
parentOID = rte->relid;
if (!has_subclass(parentOID))
{
/* Clear flag before returning */
//无子表,设置标记并返回
rte->inh = false;
return;
}
/*
* The rewriter should already have obtained an appropriate lock on each
* relation named in the query. However, for each child relation we add
* to the query, we must obtain an appropriate lock, because this will be
* the first use of those relations in the parse/rewrite/plan pipeline.
* Child rels should use the same lockmode as their parent.
* 查询rewriter程序应该已经在查询中命名的每个关系上获得了适当的锁。
* 但是，对于添加到查询中的每个子关系，必须获得适当的锁，
* 因为这将是解析/重写/计划过程中这些关系的第一次使用。
* 子树应该使用与父树相同的锁模式。
*/
lockmode = rte->rellockmode;
/* Scan for all members of inheritance set, acquire needed locks */
//扫描继承集的所有成员，获取所需的锁
inhOIDs = find_all_inheritors(parentOID, lockmode, NULL);
/*
* Check that there's at least one descendant, else treat as no-child
* case. This Could happen despite above has_subclass() check, if table
* once had a child but no longer does.
* 检查是否至少有一个后代，否则视为无子女情况。
* 尽管上面有has_subclass()检查，但如果table曾经有一个子元素，
* 但现在不再有了，则可能发生这种情况。
*/
if (list_length(inhOIDs) < 2)
{
/* Clear flag before returning */
//清除标记,返回
rte->inh = false;
return;
}
/*
* If parent relation is selected FOR UPDATE/SHARE, we need to mark its
* PlanRowMark as isParent = true, and generate a new PlanRowMark for each
* child.
* 如果父关系是 selected FOR UPDATE/SHARE，
* 则需要将其PlanRowMark标记为isParent = true，
* 并为每个子关系生成一个新的PlanRowMark。
*/
oldrc = get_plan_rowmark(root->rowMarks, rti);
if (oldrc)
oldrc->isParent = true;
/*
* Must open the parent relation to examine its tupdesc. We need not lock
* it; we assume the rewriter already did.
* 必须打开父关系以检查其tupdesc。
* 不需要锁定,我们假设查询重写已经这么做了。
*/
oldrelation = heap_open(parentOID, NoLock);
/* Scan the inheritance set and expand it */
//扫描继承集合并扩展之
if (RelationGetPartitionDesc(oldrelation) != NULL)//
{
Assert(rte->relkind == RELKIND_PARTITIONED_TABLE);
/*
* If this table has partitions, recursively expand them in the order
* in which they appear in the PartitionDesc. While at it, also
* extract the partition key columns of all the partitioned tables.
* 如果这个表有分区，则按分区在PartitionDesc中出现的顺序递归展开它们。
* 同时，还提取所有分区表的分区键列。
*/
expand_partitioned_rtentry(root, rte, rti, oldrelation, oldrc,
lockmode, &root->append_rel_list);
}
else
{
//分区描述符获取不成功(没有分区信息)
List *appinfos = NIL;
RangeTblEntry *childrte;
Index childRTindex;
/*
* This table has no partitions. Expand any plain inheritance
* children in the order the OIDs were returned by
* find_all_inheritors.
* 这个表没有分区。
* 按find_all_inheritors返回的OIDs的顺序展开所有普通继承子元素。
*/
foreach(l, inhOIDs)//遍历OIDs
{
Oid childOID = lfirst_oid(l);
Relation newrelation;
/* Open rel if needed; we already have required locks */
//如有需要，打开rel(已获得锁)
if (childOID != parentOID)
newrelation = heap_open(childOID, NoLock);
else
newrelation = oldrelation;
/*
* It is possible that the parent table has children that are temp
* tables of other backends. We cannot safely access such tables
* (because of buffering issues), and the best thing to do seems
* to be to silently ignore them.
* 父表的子表可能是其他后台的临时表。
* 我们不能安全地访问这些表(因为存在缓冲问题)，最好的办法似乎是悄悄地忽略它们。
*/
if (childOID != parentOID && RELATION_IS_OTHER_TEMP(newrelation))
{
heap_close(newrelation, lockmode);//忽略它们
continue;
}
expand_single_inheritance_child(root, rte, rti, oldrelation, oldrc,
newrelation,
&appinfos, &childrte,
&childRTindex);//展开
/* Close child relations, but keep locks */
//关闭子表,但仍持有锁
if (childOID != parentOID)
heap_close(newrelation, NoLock);
}
/*
* If all the children were temp tables, pretend it's a
* non-inheritance situation; we don't need Append node in that case.
* The duplicate RTE we added for the parent table is harmless, so we
* don't bother to get rid of it; ditto for the useless PlanRowMark
* node.
* 如果所有的子表都是临时表，则假设这是非继承情况;
* 在这种情况下，不需要APPEND NODE。
* 我们为父表添加重复的RTE是无关紧要的，
* 因此我们不必费心删除它;无用的PlanRowMark节点也是如此。
*/
if (list_length(appinfos) < 2)
rte->inh = false;//设置标记
else
root->append_rel_list = list_concat(root->append_rel_list,
appinfos);//添加到链表中
}
heap_close(oldrelation, NoLock);//关闭relation
}
/*
* expand_partitioned_rtentry
* Recursively expand an RTE for a partitioned table.
* 递归扩展分区表RTE
*/
static void
expand_partitioned_rtentry(PlannerInfo *root, RangeTblEntry *parentrte,
Index parentRTindex, Relation parentrel,
PlanRowMark *top_parentrc, LOCKMODE lockmode,
List **appinfos)
{
int i;
RangeTblEntry *childrte;
Index childRTindex;
PartitionDesc partdesc = RelationGetPartitionDesc(parentrel);
check_stack_depth();
/* A partitioned table should always have a partition descriptor. */
//分配表通常应具备分区描述符
Assert(partdesc);
Assert(parentrte->inh);
/*
* Note down whether any partition key cols are being updated. Though it's
* the root partitioned table's updatedCols we are interested in, we
* instead use parentrte to get the updatedCols. This is convenient
* because parentrte already has the root partrel's updatedCols translated
* to match the attribute ordering of parentrel.
* 请注意是否正在更新分区键cols。
* 虽然感兴趣的是根分区表的updatedCols，但是使用parentrte来获取updatedCols。
* 这很方便，因为parentrte已经将root partrel的updatedCols转换为匹配parentrel的属性顺序。
*/
if (!root->partColsUpdated)
root->partColsUpdated =
has_partition_attrs(parentrel, parentrte->updatedCols, NULL);
/* First expand the partitioned table itself. */
//
expand_single_inheritance_child(root, parentrte, parentRTindex, parentrel,
top_parentrc, parentrel,
appinfos, &childrte, &childRTindex);
/*
* If the partitioned table has no partitions, treat this as the
* non-inheritance case.
* 如果分区表没有分区，则将其视为非继承情况。
*/
if (partdesc->nparts == 0)
{
parentrte->inh = false;
return;
}
for (i = 0; i < partdesc->nparts; i++)
{
Oid childOID = partdesc->oids[i];
Relation childrel;
/* Open rel; we already have required locks */
//打开rel
childrel = heap_open(childOID, NoLock);
/*
* Temporary partitions belonging to other sessions should have been
* disallowed at deFinition, but for paranoia's sake, let's double
* check.
* 属于其他会话的临时分区在定义时应该是不允许的，但是出于偏执狂的考虑，再检查一下。
*/
if (RELATION_IS_OTHER_TEMP(childrel))
elog(ERROR, "temporary relation from another session found as partition");
//扩展之
expand_single_inheritance_child(root, parentrte, parentRTindex,
parentrel, top_parentrc, childrel,
appinfos, &childrte, &childRTindex);
/* If this child is itself partitioned, recurse */
//子关系是分区表,递归扩展
if (childrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
expand_partitioned_rtentry(root, childrte, childRTindex,
childrel, top_parentrc, lockmode,
appinfos);
/* Close child relation, but keep locks */
//关闭子关系,但仍持有锁
heap_close(childrel, NoLock);
}
}
/* expand_single_inheritance_child
* Build a RangeTblEntry and an AppendRelInfo, if appropriate, plus
* maybe a PlanRowMark.
* 构建一个RangeTblEntry和一个AppendRelInfo，如果合适的话，再加上一个PlanRowMark。
*
* We Now expand the partition hierarchy level by level, creating a
* corresponding hierarchy of AppendRelInfos and RelOptInfos, where each
* partitioned descendant acts as a parent of its immediate partitions.
* (This is a difference from what older versions of Postgresql did and what
* is still done in the case of table inheritance for unpartitioned tables,
* where the hierarchy is flattened during RTE expansion.)
* 现在我们逐层扩展分区层次结构，创建一个对应的AppendRelInfos和RelOptInfos层次结构，
* 其中每个分区的后代充当其直接分区的父级。
* (在未分区表的表继承中，
* 层次结构在RTE扩展期间被扁平化，这与老版本的Postgresql有所不同。)
*
* PlanRowMarks still carry the top-parent's RTI, and the top-parent's
* allMarkTypes field still accumulates values from all descendents.
* PlanRowMarks仍然具有顶级父类的RTI信息，
* 而顶级父类的allMarkTypes字段仍然从所有子类累积。
*
* "parentrte" and "parentRTindex" are immediate parent's RTE and
* RTI. "top_parentrc" is top parent's PlanRowMark.
* “parentrte”和“parentRTindex”是直接父级的RTE和RTI。
* “top_parentrc”是top父类的PlanRowMark。
*
* The child RangeTblEntry and its RTI are returned in "childrte_p" and
* "childRTindex_p" resp.
* 子RTE及其RTI在“childrte_p”和“childRTindex_p”resp中返回。
*/
static void
expand_single_inheritance_child(PlannerInfo *root, RangeTblEntry *parentrte,
Index parentRTindex, Relation parentrel,
PlanRowMark *top_parentrc, Relation childrel,
List **appinfos, RangeTblEntry **childrte_p,
Index *childRTindex_p)
{
Query *parse = root->parse;
Oid parentOID = RelationGetRelid(parentrel);//父关系
Oid childOID = RelationGetRelid(childrel);//子关系
RangeTblEntry *childrte;
Index childRTindex;
AppendRelInfo *appinfo;
/*
* Build an RTE for the child, and attach to query's rangetable list. We
* copy most fields of the parent's RTE, but replace relation OID and
* relkind, and set inh = false. Also, set requiredPerms to zero since
* all required permissions checks are done on the original RTE. Likewise,
* set the child's securityQuals to empty, because we only want to apply
* the parent's RLS conditions regardless of what RLS properties
* individual children may have. (This is an intentional choice to make
* inherited RLS work like regular permissions checks.) The parent
* securityQuals will be propagated to children along with other base
* restriction clauses, so we don't need to do it here.
* 为子元素构建一个RTE，并附加到query的范围表链表中。
* 我们复制父RTE的大部分字段，但是替换关系OID和relkind，并设置inh = false。
* 另外，将requiredPerms设置为0，因为所有需要的权限检查都是在原始RTE上完成的。
* 同样，将子元素securityQuals设置为空，因为只想应用父元素的RLS条件，
* 而不管每个子元素可能具有什么RLS属性。
* (这是一种有意的选择，目的是让继承的RLS像常规权限检查一样工作。)
* 父安全条件quals将与其他基本限制条款一起传播到子级，因此不需要在这里这样做。
*/
childrte = copyObject(parentrte);
*childrte_p = childrte;
childrte->relid = childOID;
childrte->relkind = childrel->rd_rel->relkind;
/* A partitioned child will need to be expanded further. */
//分区表的子关系会在"将来"扩展
if (childOID != parentOID &&
childrte->relkind == RELKIND_PARTITIONED_TABLE)
childrte->inh = true;
else
childrte->inh = false;
childrte->requiredPerms = 0;
childrte->securityQuals = NIL;
parse->rtable = lappend(parse->rtable, childrte);
childRTindex = list_length(parse->rtable);
*childRTindex_p = childRTindex;
/*
* We need an AppendRelInfo if paths will be built for the child RTE. If
* childrte->inh is true, then we'll always need to generate append paths
* for it. If childrte->inh is false, we must scan it if it's not a
* partitioned table; but if it is a partitioned table, then it never has
* any data of its own and need not be scanned.
* 如果要为子RTE构建路径，则需要一个AppendRelInfo。
* 如果children ->inh为真，那么我们总是需要为它生成APPEND访问路径。
* 如果children ->inh为假，则必须扫描它，如果它不是分区表;
* 但是如果它是一个分区表，那么它永远不会有任何自己的数据，也不需要扫描。
*/
if (childrte->relkind != RELKIND_PARTITIONED_TABLE || childrte->inh)
{
appinfo = makeNode(AppendRelInfo);
appinfo->parent_relid = parentRTindex;
appinfo->child_relid = childRTindex;
appinfo->parent_reltype = parentrel->rd_rel->reltype;
appinfo->child_reltype = childrel->rd_rel->reltype;
make_inh_translation_list(parentrel, childrel, childRTindex,
&appinfo->translated_vars);
appinfo->parent_reloid = parentOID;
*appinfos = lappend(*appinfos, appinfo);
/*
* Translate the column permissions bitmaps to the child's attnums (we
* have to build the translated_vars list before we can do this). But
* if this is the parent table, leave copyObject's result alone.
* 将列权限位图转换为子节点的attnums(在此之前必须构建translated_vars列表)。
* 但是，如果这是父表，则不要理会copyObject的结果。
*
* Note: we need to do this even though the executor won't run any
* permissions checks on the child RTE. The insertedCols/updatedCols
* bitmaps may be examined for trigger-firing purposes.
* 注意:即使执行程序不会在子RTE上运行任何权限检查，我们也需要这样做。
* 可以检查插入的tedcols /updatedCols位图是否具有触发目的。
*/
if (childOID != parentOID)
{
childrte->selectedCols = translate_col_privs(parentrte->selectedCols,
appinfo->translated_vars);
childrte->insertedCols = translate_col_privs(parentrte->insertedCols,
appinfo->translated_vars);
childrte->updatedCols = translate_col_privs(parentrte->updatedCols,
appinfo->translated_vars);
}
}
/*
* Build a PlanRowMark if parent is marked FOR UPDATE/SHARE.
* 如父关系标记为FOR UPDATE/SHARE,则创建PlanRowMark
*/
if (top_parentrc)
{
PlanRowMark *childrc = makeNode(PlanRowMark);
childrc->rti = childRTindex;
childrc->prti = top_parentrc->rti;
childrc->rowmarkId = top_parentrc->rowmarkId;
/* Reselect rowmark type, because relkind might not match parent */
//重新选择rowmark类型，因为relkind可能与父类不匹配
childrc->markType = select_rowmark_type(childrte,
top_parentrc->strength);
childrc->allMarkTypes = (1 << childrc->markType);
childrc->strength = top_parentrc->strength;
childrc->waitPolicy = top_parentrc->waitPolicy;
/*
* We mark RowMarks for partitioned child tables as parent RowMarks so
* that the executor ignores them (except their existence means that
* the child tables be locked using appropriate mode).
* 我们将分区的子表的RowMarks标记为父RowMarks，
* 以便执行程序忽略它们(除非它们的存在意味着子表使用适当的模式被锁定)。
*/
childrc->isParent = (childrte->relkind == RELKIND_PARTITIONED_TABLE);
/* Include child's rowmark type in top parent's allMarkTypes */
//在父类的allMarkTypes中包含子类的rowmark类型
top_parentrc->allMarkTypes |= childrc->allMarkTypes;
root->rowMarks = lappend(root->rowMarks, childrc);
}
}
三、跟踪分析
测试脚本如下
testdb=# explain verbose select * from t_hash_partition where c1 = 1 OR c1 = 2;
QUERY PLAN
-------------------------------------------------------------------------------------
Append (cost=0.00..30.53 rows=6 width=200)
-> Seq Scan on public.t_hash_partition_1 (cost=0.00..15.25 rows=3 width=200)
Output: t_hash_partition_1.c1, t_hash_partition_1.c2, t_hash_partition_1.c3
Filter: ((t_hash_partition_1.c1 = 1) OR (t_hash_partition_1.c1 = 2))
-> Seq Scan on public.t_hash_partition_3 (cost=0.00..15.25 rows=3 width=200)
Output: t_hash_partition_3.c1, t_hash_partition_3.c2, t_hash_partition_3.c3
Filter: ((t_hash_partition_3.c1 = 1) OR (t_hash_partition_3.c1 = 2))
(7 rows)
启动gdb,设置断点
(gdb) b expand_inherited_tables
Breakpoint 1 at 0x7e53ba: file prepunion.c, line 1483.
(gdb) c
Continuing.
Breakpoint 1, expand_inherited_tables (root=0x28fcdc8) at prepunion.c:1483
1483 nrtes = list_length(root->parse->rtable);
获取RTE的个数和链表元素
(gdb) n
1484 rl = list_head(root->parse->rtable);
(gdb)
1485 for (rti = 1; rti <= nrtes; rti++)
(gdb) p nrtes
$1 = 1
(gdb) p *rl
$2 = {data = {ptr_value = 0x28d83d0, int_value = 42828752, oid_value = 42828752}, next = 0x0}
(gdb)
循环处理RTE
(gdb) n
1487 RangeTblEntry *rte = (RangeTblEntry *) lfirst(rl);
(gdb)
1489 expand_inherited_rtentry(root, rte, rti);
(gdb) p *rte
$3 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 16986, relkind = 112 'p', tablesample = 0x0, subquery = 0x0,
security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0, funcordinality = false,
tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0, self_reference = false, coltypes = 0x0,
coltypmods = 0x0, colcollations = 0x0, enrname = 0x0, enrtuples = 0, alias = 0x0, eref = 0x28d84e8, lateral = false,
inh = true, inFromCl = true, requiredPerms = 2, checkAsUser = 0, selectedCols = 0x28d8c40, insertedCols = 0x0,
updatedCols = 0x0, securityQuals = 0x0}
进入expand_inherited_rtentry
(gdb) step
expand_inherited_rtentry (root=0x28fcdc8, rte=0x28d83d0, rti=1) at prepunion.c:1517
1517 Query *parse = root->parse;
expand_inherited_rtentry->分区表标记为T
1526 if (!rte->inh)
(gdb) p rte->inh
$4 = true
expand_inherited_rtentry->执行相关判断
(gdb) n
1529 if (rte->rtekind != RTE_RELATION)
(gdb) p rte->rtekind
$5 = RTE_RELATION
(gdb) n
1535 parentOID = rte->relid;
(gdb)
1536 if (!has_subclass(parentOID))
(gdb) p parentOID
$6 = 16986
(gdb) n
1556 oldrc = get_plan_rowmark(root->rowMarks, rti);
(gdb)
1557 if (rti == parse->resultRelation)
(gdb) p *oldrc
Cannot access memory at address 0x0
expand_inherited_rtentry->扫描继承集的所有成员，获取所需的锁,并构建OIDs链表
(gdb) n
1559 else if (oldrc && RowMarkRequiresRowShareLock(oldrc->markType))
(gdb)
1562 lockmode = AccessShareLock;
(gdb)
1565 inhOIDs = find_all_inheritors(parentOID, lockmode, NULL);
(gdb)
1572 if (list_length(inhOIDs) < 2)
(gdb) p inhOIDs
$7 = (List *) 0x28fd208
(gdb) p *inhOIDs
$8 = {type = T_OidList, length = 7, head = 0x28fd1e0, tail = 0x28fd778}
(gdb)
expand_inherited_rtentry->打开relation
(gdb) n
1584 if (oldrc)
(gdb)
1591 oldrelation = heap_open(parentOID, NoLock);
expand_inherited_rtentry->成功获取分区描述符,调用expand_partitioned_rtentry
(gdb)
1594 if (RelationGetPartitionDesc(oldrelation) != NULL)
(gdb)
1596 Assert(rte->relkind == RELKIND_PARTITIONED_TABLE);
(gdb)
1603 expand_partitioned_rtentry(root, rte, rti, oldrelation, oldrc,
(gdb)
expand_inherited_rtentry->进入expand_partitioned_rtentry
(gdb) step
expand_partitioned_rtentry (root=0x28fcdc8, parentrte=0x28d83d0, parentRTindex=1, parentrel=0x7f4e66827980,
top_parentrc=0x0, lockmode=1, appinfos=0x28fce98) at prepunion.c:1684
1684 PartitionDesc partdesc = RelationGetPartitionDesc(parentrel);
expand_partitioned_rtentry->获取分区描述符
1684 PartitionDesc partdesc = RelationGetPartitionDesc(parentrel);
(gdb) n
1686 check_stack_depth();
(gdb) p *partdesc
$9 = {nparts = 6, oids = 0x298e4f8, boundinfo = 0x298e530}
expand_partitioned_rtentry->执行相关校验
(gdb) n
1689 Assert(partdesc);
(gdb)
1691 Assert(parentrte->inh);
(gdb)
1700 if (!root->partColsUpdated)
(gdb)
1702 has_partition_attrs(parentrel, parentrte->updatedCols, NULL);
(gdb)
1701 root->partColsUpdated =
(gdb)
1705 expand_single_inheritance_child(root, parentrte, parentRTindex, parentrel,
expand_partitioned_rtentry->首先展开分区表本身,进入expand_single_inheritance_child
(gdb) step
expand_single_inheritance_child (root=0x28fcdc8, parentrte=0x28d83d0, parentRTindex=1, parentrel=0x7f4e66827980,
top_parentrc=0x0, childrel=0x7f4e66827980, appinfos=0x28fce98, childrte_p=0x7ffd1928d2f8, childRTindex_p=0x7ffd1928d2f4)
at prepunion.c:1778
1778 Query *parse = root->parse;
expand_single_inheritance_child->执行相关初始化(childrte)
(gdb) n
1779 Oid parentOID = RelationGetRelid(parentrel);
(gdb)
1780 Oid childOID = RelationGetRelid(childrel);
(gdb)
1797 childrte = copyObject(parentrte);
(gdb) p parentOID
$10 = 16986
(gdb) p childOID
$11 = 16986
(gdb) n
1798 *childrte_p = childrte;
(gdb)
1799 childrte->relid = childOID;
(gdb)
1800 childrte->relkind = childrel->rd_rel->relkind;
(gdb)
1802 if (childOID != parentOID &&
(gdb)
1806 childrte->inh = false;
(gdb)
1807 childrte->requiredPerms = 0;
(gdb)
1808 childrte->securityQuals = NIL;
(gdb)
1809 parse->rtable = lappend(parse->rtable, childrte);
(gdb)
1810 childRTindex = list_length(parse->rtable);
(gdb)
1811 *childRTindex_p = childRTindex;
(gdb) p *childrte -->relid = 16986,仍为分区表
$12 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 16986, relkind = 112 'p', tablesample = 0x0, subquery = 0x0,
security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0, funcordinality = false,
tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0, self_reference = false, coltypes = 0x0,
coltypmods = 0x0, colcollations = 0x0, enrname = 0x0, enrtuples = 0, alias = 0x0, eref = 0x28fd268, lateral = false,
inh = false, inFromCl = true, requiredPerms = 0, checkAsUser = 0, selectedCols = 0x28fd898, insertedCols = 0x0,
updatedCols = 0x0, securityQuals = 0x0}
(gdb) p *childRTindex_p
$13 = 0
expand_single_inheritance_child->完成分区表本身的扩展,回到expand_partitioned_rtentry
(gdb) p *childRTindex_p
$13 = 0
(gdb) n
1820 if (childrte->relkind != RELKIND_PARTITIONED_TABLE || childrte->inh)
(gdb)
1855 if (top_parentrc)
(gdb)
1881 }
(gdb)
expand_partitioned_rtentry (root=0x28fcdc8, parentrte=0x28d83d0, parentRTindex=1, parentrel=0x7f4e66827980,
top_parentrc=0x0, lockmode=1, appinfos=0x28fce98) at prepunion.c:1713
1713 if (partdesc->nparts == 0)
expand_partitioned_rtentry->开始遍历分区描述符中的分区
1713 if (partdesc->nparts == 0)
(gdb) n
1719 for (i = 0; i < partdesc->nparts; i++)
(gdb)
1721 Oid childOID = partdesc->oids[i];
(gdb)
1725 childrel = heap_open(childOID, NoLock);
(gdb)
1732 if (RELATION_IS_OTHER_TEMP(childrel))
(gdb)
1735 expand_single_inheritance_child(root, parentrte, parentRTindex,
(gdb) p childOID
$14 = 16989
----------------------------------------
testdb=# select relname from pg_class where oid=16989;
relname
--------------------
t_hash_partition_1
(1 row)
----------------------------------------
expand_single_inheritance_child->再次进入expand_single_inheritance_child
(gdb) step
expand_single_inheritance_child (root=0x28fcdc8, parentrte=0x28d83d0, parentRTindex=1, parentrel=0x7f4e66827980,
top_parentrc=0x0, childrel=0x7f4e668306a0, appinfos=0x28fce98, childrte_p=0x7ffd1928d2f8, childRTindex_p=0x7ffd1928d2f4)
at prepunion.c:1778
1778 Query *parse = root->parse;
expand_single_inheritance_child->开始构建AppendRelInfo
...
1820 if (childrte->relkind != RELKIND_PARTITIONED_TABLE || childrte->inh)
(gdb)
1822 appinfo = makeNode(AppendRelInfo);
(gdb) p *childrte
$17 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 16989, relkind = 114 'r', tablesample = 0x0, subquery = 0x0,
security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0, funcordinality = false,
tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0, self_reference = false, coltypes = 0x0,
coltypmods = 0x0, colcollations = 0x0, enrname = 0x0, enrtuples = 0, alias = 0x0, eref = 0x28fd9d0, lateral = false,
inh = false, inFromCl = true, requiredPerms = 0, checkAsUser = 0, selectedCols = 0x28fdbc8, insertedCols = 0x0,
updatedCols = 0x0, securityQuals = 0x0}
(gdb) p *childrte->relkind
Cannot access memory at address 0x72
(gdb) p childrte->relkind
$18 = 114 'r'
(gdb) p childrte->inh
$19 = false
expand_single_inheritance_child->构建完毕,查看AppendRelInfo结构体
(gdb) n
1823 appinfo->parent_relid = parentRTindex;
(gdb)
1824 appinfo->child_relid = childRTindex;
(gdb)
1825 appinfo->parent_reltype = parentrel->rd_rel->reltype;
(gdb)
1826 appinfo->child_reltype = childrel->rd_rel->reltype;
(gdb)
1827 make_inh_translation_list(parentrel, childrel, childRTindex,
(gdb)
1829 appinfo->parent_reloid = parentOID;
(gdb)
1830 *appinfos = lappend(*appinfos, appinfo);
(gdb)
1841 if (childOID != parentOID)
(gdb)
1843 childrte->selectedCols = translate_col_privs(parentrte->selectedCols,
(gdb)
1845 childrte->insertedCols = translate_col_privs(parentrte->insertedCols,
(gdb)
1847 childrte->updatedCols = translate_col_privs(parentrte->updatedCols,
(gdb)
1855 if (top_parentrc)
(gdb) p *appinfo
$20 = {type = T_AppendRelInfo, parent_relid = 1, child_relid = 3, parent_reltype = 16988, child_reltype = 16991,
translated_vars = 0x28fdc90, parent_reloid = 16986}
expand_single_inheritance_child->完成调用,返回
(gdb)
1855 if (top_parentrc)
(gdb) p *appinfo
$20 = {type = T_AppendRelInfo, parent_relid = 1, child_relid = 3, parent_reltype = 16988, child_reltype = 16991,
translated_vars = 0x28fdc90, parent_reloid = 16986}
(gdb) n
1881 }
(gdb)
expand_partitioned_rtentry (root=0x28fcdc8, parentrte=0x28d83d0, parentRTindex=1, parentrel=0x7f4e66827980,
top_parentrc=0x0, lockmode=1, appinfos=0x28fce98) at prepunion.c:1740
1740 if (childrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
expand_inherited_rtentry->完成expand_partitioned_rtentry过程调用,回到expand_inherited_rtentry
(gdb) finish
Run till exit from #0 expand_partitioned_rtentry (root=0x28fcdc8, parentrte=0x28d83d0, parentRTindex=1,
parentrel=0x7f4e66827980, top_parentrc=0x0, lockmode=1, appinfos=0x28fce98) at prepunion.c:1740
0x00000000007e55e3 in expand_inherited_rtentry (root=0x28fcdc8, rte=0x28d83d0, rti=1) at prepunion.c:1603
1603 expand_partitioned_rtentry(root, rte, rti, oldrelation, oldrc,
(gdb)
expand_inherited_rtentry->完成expand_inherited_rtentry的调用,回到expand_inherited_tables
(gdb) n
1665 heap_close(oldrelation, NoLock);
(gdb)
1666 }
(gdb)
expand_inherited_tables (root=0x28fcdc8) at prepunion.c:1490
1490 rl = lnext(rl);
(gdb)
expand_inherited_tables->完成expand_inherited_tables调用,回到subquery_planner
(gdb) n
1485 for (rti = 1; rti <= nrtes; rti++)
(gdb)
1492 }
(gdb)
subquery_planner (glob=0x28fcd30, parse=0x28d82b8, parent_root=0x0, hasRecursion=false, tuple_fraction=0) at planner.c:719
719 root->hasHavingQual = (parse->havingQual != NULL);
(gdb)
DONE!
四、参考资料
Parallel Append implementation
Partition Elimination in Postgresql 11
