PostgreSQL 原始碼解讀（98）- 分割槽表#4（資料查詢路由#1-“擴充套件”分割槽表）
在查詢分割槽表的時候PG如何確定查詢的是哪個分割槽？如何確定？相關的機制是什麼？接下來幾個章節將一一介紹，本節是第一部分。
零、實現機制
我們先看下面的例子,兩個普通表t_normal_1和t_normal_2,執行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)
兩張普通表的UNION ALL,PG使用APPEND運算子把t_normal_1順序掃描的結果集和t_normal_2順序掃描的結果集"APPEND"在一起作為最終的結果集輸出.
分割槽表的查詢也是類似的機制,把各個分割槽的結果集APPEND在一起,然後作為最終的結果集輸出,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)
查詢分割槽表t_hash_partition,條件為c1 = 1 OR c1 = 2,從執行計劃可見是把t_hash_partition_1順序掃描的結果集和t_hash_partition_3順序掃描的結果集"APPEND"在一起作為最終的結果集輸出.
這裡面有幾個問題需要解決:
1.識別分割槽表並找到所有的分割槽子表;
2.根據約束條件識別需要查詢的分割槽,這是出於效能的考慮;
3.對結果集執行APPEND,作為最終結果輸出.
本節介紹了PG如何識別分割槽表並找到所有的分割槽子表,實現的函式是expand_inherited_tables.
一、資料結構
AppendRelInfo
Append-relation資訊.
當我們將可繼承表(分割槽表)或UNION-ALL子查詢展開為“追加關係”(本質上是子RTE的連結串列)時，為每個子RTE構建一個AppendRelInfo。
AppendRelInfos連結串列指示在展開父節點時必須包含哪些子rte，每個節點具有將引用父節點的Vars轉換為引用該子節點的Vars所需的所有資訊。
/*
* Append-relation info.
* Append-relation資訊.
*
* 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.
* 當我們將可繼承表(分割槽表)或UNION-ALL子查詢展開為“追加關係”(本質上是子RTE的連結串列)時，
* 為每個子RTE構建一個AppendRelInfo。
* AppendRelInfos連結串列指示在展開父節點時必須包含哪些子rte，
* 每個節點具有將引用父節點的Vars轉換為引用該子節點的Vars所需的所有資訊。
*
* 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.
* 這些結構體儲存在PlannerInfo節點的append_rel_list中。
* 注意，只是將所有的結構體放入一個連結串列中，並在希望展開任何父類時掃描整個連結串列。
* 本可以使用更復雜的資料結構(例如，每個父節點一個列表)，
* 但是在提取子查詢之類的操作中更新它會更困難，
* 而且實際上也不會更容易掃描。
* 考慮到典型的查詢不會有很多不同的附加項，因此似乎不值得將事情複雜化。
*
* 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:計劃準備階段完成後,
* 當且僅當它的“inh”標誌已設定時,給定的RTE是一個append parent在append_rel_list中的一個條目。
* 我們為沒有child的平面表清除“inh”標記,
* 同時(有濫用標記的嫌疑)為UNION ALL查詢中的子查詢RTEs設定“inh”標記。
* 這樣可以避免對append_rel_list進行無用的搜尋。
*
* 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:資料結構假定附加的rel成員是獨立的baserels。
* 這對於繼承來說是可以的，但是如果UNION ALL member子查詢包含一個join，
* 那麼它將阻止我們提取UNION ALL member子查詢。
* 雖然可以用更復雜的資料結構解決這個問題，但目前沒有太大意義，因為該計劃可能不會有任何改進。
*/
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.
* 這些欄位惟一地標識這個append relationship。
* 對於同一個parent_relid可以有(實際上應該總是)多個AppendRelInfos，
* 但是每個child_relid不能有多個AppendRelInfos，
* 因為給定的RTE不能是多個append parent的子節點。
*/
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.
* 對於繼承appendrel，父類和子類都是普通關係，
* 我們將它們的rowtype OIDs儲存在這裡，用於轉換whole-row Vars。
* 對於UNION-ALL appendrel，父查詢和子查詢都是沒有指定行型別的子查詢，
* 我們在這裡儲存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.
* 這個列表的第N個元素是一個Var或表示式，表示與父元素的第N列對應的子列。
* 這用於將引用parent rel的Vars轉換為對子rel的引用。
* 如果連結串列元素與父元素的已刪除列相對應，則該元素為NULL
* (這隻適用於繼承情況，而不是UNION ALL)。
* 對於繼承情況，連結串列元素總是簡單的變數，但是可以是UNION ALL情況下的任意表示式。
*
* 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，我們只儲存使用者列的條目(attno > 0)。
* Whole-row Vars是大小寫敏感的，系統列(attno < 0)不需要特別的轉換，
* 因為它們的attno對所有表都是相同的。
*
* Caution: the Vars have varlevelsup = 0. Be careful to adjust as needed
* when copying into a subquery.
* 注意:Vars的varlevelsup = 0。
* 在將資料複製到子查詢時，要注意根據需要進行調整。
*/
//child's Vars中的表示式
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.
* 我們將父表的OID儲存在這裡用於繼承，
* 如為UNION ALL,則這裡儲存的是InvalidOid。
* 只有在試圖引用已刪除的父列時，才需要這樣做來幫助生成錯誤訊息。
*/
Oid parent_reloid; /* OID of parent relation */
} AppendRelInfo;
PlannerInfo
該資料結構用於儲存查詢語句在規劃/最佳化過程中的相關資訊
/*----------
* PlannerInfo
* Per-query information for planning/optimization
* 用於規劃/最佳化的每個查詢資訊
*
* 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.
* 在所有計劃程式例程中，這個結構通常稱為“root”。
* 除了原始查詢之外，它還儲存到所有計劃器工作狀態的連結。
* 注意，目前計劃器會毫無節制的修改傳入的查詢資料結構,相信總有一天這種情況會停止的。
*----------
*/
struct AppendRelInfo;
typedef struct PlannerInfo
{
NodeTag type;//Node標識
//查詢樹
Query *parse; /* the Query being planned */
//當前的planner全域性資訊
PlannerGlobal *glob; /* global info for current planner run */
//查詢層次,1標識最高層
Index query_level; /* 1 at the outermost Query */
// 如為子計劃,則這裡儲存父計劃器指標,NULL標識最高層
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包含該查詢級別需要提供給當前計劃的較低查詢級別的表示式。
* outer_params包含PARAM_EXEC Params的引數，外部查詢級別將使該查詢級別可用這些引數。
*/
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儲存指向“base rels”和“other rels”的指標
* (有關RelOptInfo的更多資訊，請參見注釋)。
* 它由可範圍表索引建立索引(因此條目0總是被浪費)。
* 當RTE與基本關係(如JOIN RTE或未被引用的檢視RTE時)不相對應
* 或者如果RelOptInfo還沒有生成，條目可以為NULL。
*/
//RelOptInfo陣列,儲存"base rels",比如基表/子查詢等.
//該陣列與RTE的順序一一對應,而且是從1開始,因此[0]無用 */
struct RelOptInfo **simple_rel_array; /* All 1-rel RelOptInfos */
int simple_rel_array_size; /* 陣列大小,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的長度與simple_rel_array相同，
* 並儲存指向相應範圍表條目的指標。
* 這使我們可以避免執行rt_fetch()，因為一旦擴充套件了大型繼承集，rt_fetch()可能會有點慢。
*/
//RTE陣列
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與上述陣列的長度相同，
* 並儲存指向對應的AppendRelInfo條目的指標，該條目由child_relid索引，
* 如果沒有索引則為NULL。
* 如果append_rel_list為空，則不分配陣列本身。
*/
//處理集合操作如UNION ALL時使用和分割槽表時使用
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是查詢中所有base relids(但不是“other” relids)的一個Relids集合;
* 也就是說，這是需要形成的最終連線的Relids識別符號。
* 這是在開始建立路徑之前在make_one_rel中計算的。
*/
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中的某些外連線中值可為空的base Relids集合;
* 這些是在WHERE子句、SELECT targetlist等下面可能為空的樹。
* 這是在deconstruct_jointree中處理獲得的。
*/
//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是在計劃執行中考慮的所有連線關係RelOptInfos的連結串列。
* 對於小問題，只需要掃描連結串列執行查詢，但是當存在許多連線關係時，
* 需要構建一個雜湊表來進行更快的查詢。
* 當join_rel_hash不為空時，雜湊表是有效可用於查詢的。
* 注意，即使在使用雜湊表進行查詢時，仍然維護該連結串列;這簡化了GEQO(遺傳演算法)的生命週期。
*/
//參與連線的Relation的RelOptInfo連結串列
List *join_rel_list; /* list of join-relation RelOptInfos */
//可加快連結串列訪問的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.
* 在執行動態規劃演算法的連線搜尋時，join_rel_level[k]是k級的所有連線關係RelOptInfos的列表，
* join_cur_level是當前級別。
* 新的連線關係RelOptInfos會自動新增到join_rel_level[join_cur_level]連結串列中。
* 如果不使用join_rel_level，則為NULL。
*/
//RelOptInfo指標連結串列陣列,k層的join儲存在[k]中
List **join_rel_level; /* lists of join-relation RelOptInfos */
//當前的join層次
int join_cur_level; /* index of list being extended */
//查詢的初始化計劃連結串列
List *init_plans; /* init SubPlans for query */
//CTE子計劃ID連結串列
List *cte_plan_ids; /* per-CTE-item list of subplan IDs */
//MULTIEXPR子查詢輸出的引數連結串列的連結串列
List *multiexpr_params; /* List of Lists of Params for MULTIEXPR
* subquery outputs */
//活動的等價類連結串列
List *eq_classes; /* list of active EquivalenceClasses */
//規範化的PathKey連結串列
List *canon_pathkeys; /* list of "canonical" PathKeys */
//外連線約束條件連結串列(左)
List *left_join_clauses; /* list of RestrictInfos for mergejoinable
* outer join clauses w/nonnullable var on
* left */
//外連線約束條件連結串列(右)
List *right_join_clauses; /* list of RestrictInfos for mergejoinable
* outer join clauses w/nonnullable var on
* right */
//全連線約束條件連結串列
List *full_join_clauses; /* list of RestrictInfos for mergejoinable
* full join clauses */
//特殊連線資訊連結串列
List *join_info_list; /* list of SpecialJoinInfos */
//AppendRelInfo連結串列
List *append_rel_list; /* list of AppendRelInfos */
//PlanRowMarks連結串列
List *rowMarks; /* list of PlanRowMarks */
//PHI連結串列
List *placeholder_list; /* list of PlaceHolderInfos */
// 外來鍵資訊連結串列
List *fkey_list; /* list of ForeignKeyOptInfos */
//query_planner()要求的PathKeys連結串列
List *query_pathkeys; /* desired pathkeys for query_planner() */
//分組子句路徑鍵
List *group_pathkeys; /* groupClause pathkeys, if any */
//視窗函式路徑鍵
List *window_pathkeys; /* pathkeys of bottom window, if any */
//distinctClause路徑鍵
List *distinct_pathkeys; /* distinctClause pathkeys, if any */
//排序路徑鍵
List *sort_pathkeys; /* sortClause pathkeys, if any */
//已規範化的分割槽Schema
List *part_schemes; /* Canonicalised partition schemes used in the
* query. */
//嘗試連線的RelOptInfo連結串列
List *initial_rels; /* RelOptInfos we are now trying to join */
/* Use fetch_upper_rel() to get any particular upper rel */
//上層的RelOptInfo連結串列
List *upper_rels[UPPERREL_FINAL + 1]; /* upper-rel RelOptInfos */
/* Result tlists chosen by grouping_planner for upper-stage processing */
//grouping_planner為上層處理選擇的結果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在這裡傳回它最終處理過的targetlist，用於重新標記已完成計劃的最頂層tlist。
*/
////最後需處理的投影列
List *processed_tlist;
/* Fields filled during create_plan() for use in setrefs.c */
//setrefs.c中在create_plan()函式呼叫期間填充的欄位
//分組函式屬性對映
AttrNumber *grouping_map; /* for GroupingFunc fixup */
//MinMaxAggInfos連結串列
List *minmax_aggs; /* List of MinMaxAggInfos */
//記憶體上下文
MemoryContext planner_cxt; /* context holding PlannerInfo */
//關係的page計數
double total_table_pages; /* # of pages in all tables of query */
//query_planner輸入引數:元組處理比例
double tuple_fraction; /* tuple_fraction passed to query_planner */
//query_planner輸入引數:limit_tuple
double limit_tuples; /* limit_tuples passed to query_planner */
//表示式的最小安全等級
Index qual_security_level; /* minimum security_level for quals */
/* Note: qual_security_level is zero if there are no securityQuals */
//注意:如果沒有securityQuals, 則qual_security_level是NULL(0)
//如目標relation是分割槽表的child/partition/分割槽表,則透過此欄位標記
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 */
//是否存在標記為LATERAL的RTE
bool hasLateralRTEs; /* true if any RTEs are marked LATERAL */
//是否存在已在jointree刪除的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 */
//如約束條件中存在pseudoconstant = true,則此欄位為T
bool hasPseudoConstantQuals; /* true if any RestrictInfo has
* pseudoconstant = true */
//是否存在遞迴語句
bool hasRecursion; /* true if planning a recursive WITH item */
/* These fields are used only when hasRecursion is true: */
//這些欄位僅在hasRecursion為T時使用:
//工作表的PARAM_EXEC ID
int wt_param_id; /* PARAM_EXEC ID for the work table */
//非遞迴模式的訪問路徑
struct Path *non_recursive_path; /* a path for non-recursive term */
/* These fields are workspace for createplan.c */
//這些欄位用於createplan.c
//當前節點之上的外部rels
Relids curOuterRels; /* outer rels above current node */
//未賦值的NestLoopParams引數
List *curOuterParams; /* not-yet-assigned NestLoopParams */
/* optional private data for join_search_hook, e.g., GEQO */
//可選的join_search_hook私有資料，例如GEQO
void *join_search_private;
/* Does this query modify any partition key columns? */
//該查詢是否更新分割槽鍵列?
bool partColsUpdated;
} PlannerInfo;
二、原始碼解讀
expand_inherited_tables函式將表示繼承集合的每個範圍表條目展開為“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.
* 將表示繼承集合的每個範圍表條目展開為“append relation”。
* 在這個過程結束時，“inh”標誌被設定在所有且只有那些作為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可以新增RTEs到parse->rtable中。
* 這個函式被期望遞迴地處理它用inh = true建立的所有RTEs。
* 所以只要掃描到rtable連結串列最開始的末尾即可。
*/
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.
* 檢查範圍表條目是否表示繼承集合。
* 如是，將所有子表的條目新增到查詢的範圍表中，
* 併為所有子表構建AppendRelInfo節點，並將它們新增到root->append_rel_list。
* 如沒有，清除條目的“inh”標誌，以防止以後的程式碼尋找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被認為代表了整個繼承集合。
* 生成的第一個RTE是同一個表的RTE，但inh = false表示父表作為繼承集的一個簡單成員的角色。
*
* 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.
* 無子表的關係永遠不會被認為是繼承集合。
* 對於常規繼承，父RTE必須始終至少有兩個相關的AppendRelInfos:
* 一個作為繼承集的簡單成員與父表相對應，
* 另一個或多個與實際的子表相對應。
* 因為沒有掃描分割槽表，所以它可能只有一個關聯的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? */
//是否分割槽表?
if (!rte->inh)
return;
/* Ignore any already-expanded UNION ALL nodes */
//忽略所有已擴充套件的UNION ALL節點
if (rte->rtekind != RTE_RELATION)
{
Assert(rte->rtekind == RTE_SUBQUERY);
return;//返回
}
/* Fast path for common case of childless table */
//對於常規的無子表的關係,快速判斷
parentOID = rte->relid;
if (!has_subclass(parentOID))
{
/* Clear flag before returning */
//無子表,設定標記並返回
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.
* 查詢rewriter程式應該已經在查詢中命名的每個關係上獲得了適當的鎖。
* 但是，對於新增到查詢中的每個子關係，必須獲得適當的鎖，
* 因為這將是解析/重寫/計劃過程中這些關係的第一次使用。
* 子樹應該使用與父樹相同的鎖模式。
*/
lockmode = rte->rellockmode;
/* Scan for all members of inheritance set, acquire needed locks */
//掃描繼承集的所有成員，獲取所需的鎖
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.
* 檢查是否至少有一個後代，否則視為無子女情況。
* 儘管上面有has_subclass()檢查，但如果table曾經有一個子元素，
* 但現在不再有了，則可能發生這種情況。
*/
if (list_length(inhOIDs) < 2)
{
/* Clear flag before returning */
//清除標記,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.
* 如果父關係是 selected FOR UPDATE/SHARE，
* 則需要將其PlanRowMark標記為isParent = true，
* 併為每個子關係生成一個新的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.
* 必須開啟父關係以檢查其tupdesc。
* 不需要鎖定,我們假設查詢重寫已經這麼做了。
*/
oldrelation = heap_open(parentOID, NoLock);
/* Scan the inheritance set and expand it */
//掃描繼承集合並擴充套件之
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.
* 如果這個表有分割槽，則按分割槽在PartitionDesc中出現的順序遞迴展開它們。
* 同時，還提取所有分割槽表的分割槽鍵列。
*/
expand_partitioned_rtentry(root, rte, rti, oldrelation, oldrc,
lockmode, &root->append_rel_list);
}
else
{
//分割槽描述符獲取不成功(沒有分割槽資訊)
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.
* 這個表沒有分割槽。
* 按find_all_inheritors返回的OIDs的順序展開所有普通繼承子元素。
*/
foreach(l, inhOIDs)//遍歷OIDs
{
Oid childOID = lfirst_oid(l);
Relation newrelation;
/* Open rel if needed; we already have required locks */
//如有需要，開啟rel(已獲得鎖)
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後臺的臨時表。
* 我們不能安全地訪問這些表(因為存在緩衝問題)，最好的辦法似乎是悄悄地忽略它們。
*/
if (childOID != parentOID && RELATION_IS_OTHER_TEMP(newrelation))
{
heap_close(newrelation, lockmode);//忽略它們
continue;
}
expand_single_inheritance_child(root, rte, rti, oldrelation, oldrc,
newrelation,
&appinfos, &childrte,
&childRTindex);//展開
/* Close child relations, but keep locks */
//關閉子表,但仍持有鎖
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臨時表，則假設這是非繼承情況;
* 在這種情況下，不需要APPEND NODE。
* 我們為父表新增重複的RTE是無關緊要的，
* 因此我們不必費心刪除它;無用的PlanRowMark節點也是如此。
*/
if (list_length(appinfos) < 2)
rte->inh = false;//設定標記
else
root->append_rel_list = list_concat(root->append_rel_list,
appinfos);//新增到連結串列中
}
heap_close(oldrelation, NoLock);//關閉relation
}
/*
* expand_partitioned_rtentry
* Recursively expand an RTE for a partitioned table.
* 遞迴擴充套件分割槽表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. */
//分配表通常應具備分割槽描述符
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.
* 請注意是否正在更新分割槽鍵cols。
* 雖然感興趣的是根分割槽表的updatedCols，但是使用parentrte來獲取updatedCols。
* 這很方便，因為parentrte已經將root partrel的updatedCols轉換為匹配parentrel的屬性順序。
*/
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.
* 如果分割槽表沒有分割槽，則將其視為非繼承情況。
*/
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 */
//開啟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.
* 屬於其他會話的臨時分割槽在定義時應該是不允許的，但是出於偏執狂的考慮，再檢查一下。
*/
if (RELATION_IS_OTHER_TEMP(childrel))
elog(ERROR, "temporary relation from another session found as partition");
//擴充套件之
expand_single_inheritance_child(root, parentrte, parentRTindex,
parentrel, top_parentrc, childrel,
appinfos, &childrte, &childRTindex);
/* If this child is itself partitioned, recurse */
//子關係是分割槽表,遞迴擴充套件
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 */
//關閉子關係,但仍持有鎖
heap_close(childrel, NoLock);
}
}
/* expand_single_inheritance_child
* Build a RangeTblEntry and an AppendRelInfo, if appropriate, plus
* maybe a PlanRowMark.
* 構建一個RangeTblEntry和一個AppendRelInfo，如果合適的話，再加上一個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.)
* 現在我們逐層擴充套件分割槽層次結構，建立一個對應的AppendRelInfos和RelOptInfos層次結構，
* 其中每個分割槽的後代充當其直接分割槽的父級。
* (在未分割槽表的表繼承中，
* 層次結構在RTE擴充套件期間被扁平化，這與老版本的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仍然具有頂級父類的RTI資訊，
* 而頂級父類的allMarkTypes欄位仍然從所有子類累積。
*
* "parentrte" and "parentRTindex" are immediate parent's RTE and
* RTI. "top_parentrc" is top parent's PlanRowMark.
* “parentrte”和“parentRTindex”是直接父級的RTE和RTI。
* “top_parentrc”是top父類的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);//父關係
Oid childOID = RelationGetRelid(childrel);//子關係
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.
* 為子元素構建一個RTE，並附加到query的範圍錶連結串列中。
* 我們複製父RTE的大部分欄位，但是替換關係OID和relkind，並設定inh = false。
* 另外，將requiredPerms設定為0，因為所有需要的許可權檢查都是在原始RTE上完成的。
* 同樣，將子元素securityQuals設定為空，因為只想應用父元素的RLS條件，
* 而不管每個子元素可能具有什麼RLS屬性。
* (這是一種有意的選擇，目的是讓繼承的RLS像常規許可權檢查一樣工作。)
* 父安全條件quals將與其他基本限制條款一起傳播到子級，因此不需要在這裡這樣做。
*/
childrte = copyObject(parentrte);
*childrte_p = childrte;
childrte->relid = childOID;
childrte->relkind = childrel->rd_rel->relkind;
/* A partitioned child will need to be expanded further. */
//分割槽表的子關係會在"將來"擴充套件
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.
* 如果要為子RTE構建路徑，則需要一個AppendRelInfo。
* 如果children ->inh為真，那麼我們總是需要為它生成APPEND訪問路徑。
* 如果children ->inh為假，則必須掃描它，如果它不是分割槽表;
* 但是如果它是一個分割槽表，那麼它永遠不會有任何自己的資料，也不需要掃描。
*/
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.
* 將列許可權點陣圖轉換為子節點的attnums(在此之前必須構建translated_vars列表)。
* 但是，如果這是父表，則不要理會copyObject的結果。
*
* 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:即使執行程式不會在子RTE上執行任何許可權檢查，我們也需要這樣做。
* 可以檢查插入的tedcols /updatedCols點陣圖是否具有觸發目的。
*/
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.
* 如父關係標記為FOR UPDATE/SHARE,則建立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 */
//重新選擇rowmark型別，因為relkind可能與父類不匹配
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).
* 我們將分割槽的子表的RowMarks標記為父RowMarks，
* 以便執行程式忽略它們(除非它們的存在意味著子表使用適當的模式被鎖定)。
*/
childrc->isParent = (childrte->relkind == RELKIND_PARTITIONED_TABLE);
/* Include child's rowmark type in top parent's allMarkTypes */
//在父類的allMarkTypes中包含子類的rowmark型別
top_parentrc->allMarkTypes |= childrc->allMarkTypes;
root->rowMarks = lappend(root->rowMarks, childrc);
}
}
三、跟蹤分析
測試指令碼如下
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)
啟動gdb,設定斷點
(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);
獲取RTE的個數和連結串列元素
(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)
迴圈處理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}
進入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->分割槽表標記為T
1526 if (!rte->inh)
(gdb) p rte->inh
$4 = true
expand_inherited_rtentry->執行相關判斷
(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->掃描繼承集的所有成員，獲取所需的鎖,並構建OIDs連結串列
(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->開啟relation
(gdb) n
1584 if (oldrc)
(gdb)
1591 oldrelation = heap_open(parentOID, NoLock);
expand_inherited_rtentry->成功獲取分割槽描述符,呼叫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->進入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->獲取分割槽描述符
1684 PartitionDesc partdesc = RelationGetPartitionDesc(parentrel);
(gdb) n
1686 check_stack_depth();
(gdb) p *partdesc
$9 = {nparts = 6, oids = 0x298e4f8, boundinfo = 0x298e530}
expand_partitioned_rtentry->執行相關校驗
(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->首先展開分割槽表本身,進入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->執行相關初始化(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,仍為分割槽表
$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->完成分割槽表本身的擴充套件,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->開始遍歷分割槽描述符中的分割槽
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->再次進入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->開始構建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->構建完畢,檢視AppendRelInfo結構體
(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->完成呼叫,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過程呼叫,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的呼叫,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呼叫,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、參考資料
Parallel Append implementation
Partition Elimination in PostgreSQL 11
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/6906/viewspace-2374792/，如需轉載，請註明出處，否則將追究法律責任。
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