支援資料表分割

Aurora PostgreSQL 查詢計畫管理 (QPM) 在下列版本中支援宣告式資料表分割：

15.3 版和更新的 15 版本
14.8 版和更新的 14 版本
13.11 版和更新的 13 版本

如需詳細資訊，請參閱資料表分割。

主題

設定資料表分割
擷取資料表分割的計畫
強制執行資料表分割計畫
命名慣例

設定資料表分割

若要在 Aurora PostgreSQL QPM 中設定資料表分割，請執行以下操作：

在資料庫叢集參數群組中將 apg_plan_mgmt.plan_hash_version 設為 3 或以上。
導覽至使用查詢計畫管理且在 apg_plan_mgmt.dba_plans 檢視中具有項目的資料庫。
呼叫 apg_plan_mgmt.validate_plans('update_plan_hash') 以更新計畫資料表中的 plan_hash 值。
針對已啟用查詢計畫管理且在 apg_plan_mgmt.dba_plans 檢視中具有項目的所有資料庫重複步驟 2-3。

如需這些參數的詳細資訊，請參閱 Aurora PostgreSQL 查詢計劃管理的參數參考。

擷取資料表分割的計畫

在 QPM 中，不同的計畫依其 plan_hash 值區分。若要了解 plan_hash 如何變更，你必須首先了解類似的計畫種類。

在附加節點層級累積的存取方法、去除數字索引名稱和去除數字分割區名稱，其組合必須始終如一，才能將計畫視為相同。計畫中存取的特定分割區並不重要。在下列範例中，會建立具有 4 個分割區的資料表 tbl_a。


postgres=>create table tbl_a(i int, j int, k int, l int, m int) partition by range(i);
CREATE TABLE
postgres=>create table tbl_a1 partition of tbl_a for values from (0) to (1000);
CREATE TABLE
postgres=>create table tbl_a2 partition of tbl_a for values from (1001) to (2000);
CREATE TABLE
postgres=>create table tbl_a3 partition of tbl_a for values from (2001) to (3000);
CREATE TABLE
postgres=>create table tbl_a4 partition of tbl_a for values from (3001) to (4000);
CREATE TABLE
postgres=>create index t_i on tbl_a using btree (i);
CREATE INDEX
postgres=>create index t_j on tbl_a using btree (j);
CREATE INDEX
postgres=>create index t_k on tbl_a using btree (k);
CREATE INDEX

下列計畫會視為相同，因為無論查詢查閱的分割區數目為何，都會使用單一掃瞄方法掃描 tbl_a。


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 999 and j < 9910 and k > 50;
            
                        QUERY PLAN
-------------------------------------------------------------------
Seq Scan on tbl_a1 tbl_a
    Filter: ((i >= 990) AND (i <= 999) AND (j < 9910) AND (k > 50))
SQL Hash: 1553185667, Plan Hash: -694232056
(3 rows)


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 1100 and j < 9910 and k > 50;
            
                        QUERY PLAN
-------------------------------------------------------------------
Append
    ->  Seq Scan on tbl_a1 tbl_a_1
            Filter: ((i >= 990) AND (i <= 1100) AND (j < 9910) AND (k > 50))
    ->  Seq Scan on tbl_a2 tbl_a_2
            Filter: ((i >= 990) AND (i <= 1100) AND (j < 9910) AND (k > 50))
    SQL Hash: 1553185667, Plan Hash: -694232056
    (6 rows)


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 2100 and j < 9910 and k > 50;
            
                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Seq Scan on tbl_a1 tbl_a_1
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a3 tbl_a_3
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
 SQL Hash: 1553185667, Plan Hash: -694232056
(8 rows)

下列 3 個計畫也視為相同，因為在父層級，存取方法、去除數字索引名稱和去除數字分割區名稱為 SeqScan tbl_a、IndexScan (i_idx) tbl_a。


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 1100 and j < 9910 and k > 50;
            
                                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Seq Scan on tbl_a1 tbl_a_1
         Filter: ((i >= 990) AND (i <= 1100) AND (j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a2_i_idx on tbl_a2 tbl_a_2
         Index Cond: ((i >= 990) AND (i <= 1100))
         Filter: ((j < 9910) AND (k > 50))
 SQL Hash: 1553185667, Plan Hash: -993736942
(7 rows)


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 2100 and j < 9910 and k > 50;
            
                                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Index Scan using tbl_a1_i_idx on tbl_a1 tbl_a_1
         Index Cond: ((i >= 990) AND (i <= 2100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a3_i_idx on tbl_a3 tbl_a_3
         Index Cond: ((i >= 990) AND (i <= 2100))
         Filter: ((j < 9910) AND (k > 50))
 SQL Hash: 1553185667, Plan Hash: -993736942
(10 rows)


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 3100 and j < 9910 and k > 50;
            
                                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Seq Scan on tbl_a1 tbl_a_1
         Filter: ((i >= 990) AND (i <= 3100) AND (j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 3100) AND (j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a3 tbl_a_3
         Filter: ((i >= 990) AND (i <= 3100) AND (j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a4_i_idx on tbl_a4 tbl_a_4
         Index Cond: ((i >= 990) AND (i <= 3100))
         Filter: ((j < 9910) AND (k > 50))
 SQL Hash: 1553185667, Plan Hash: -993736942
(11 rows)

無論子分割區中的順序和出現次數是否不同，存取方法、去除數字索引名稱和去除數字分割區名稱在上述每個計畫的父層級始終如一。

不過，如果滿足以下任何條件，則計畫將視為不同：

計畫中使用任何額外的存取方法。


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 2100 and j < 9910 and k > 50;
                    
                                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Seq Scan on tbl_a1 tbl_a_1
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
   ->  Bitmap Heap Scan on tbl_a3 tbl_a_3
         Recheck Cond: ((i >= 990) AND (i <= 2100))
         Filter: ((j < 9910) AND (k > 50))
         ->  Bitmap Index Scan on tbl_a3_i_idx
               Index Cond: ((i >= 990) AND (i <= 2100))
 SQL Hash: 1553185667, Plan Hash: 1134525070
(11 rows)

計畫中的任何存取方法已不再使用。


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 1100 and j < 9910 and k > 50;
                    
                               QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Seq Scan on tbl_a1 tbl_a_1
         Filter: ((i >= 990) AND (i <= 1100) AND (j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 1100) AND (j < 9910) AND (k > 50))
 SQL Hash: 1553185667, Plan Hash: -694232056
(6 rows)

與索引方法相關聯的索引發生變更。


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 1100 and j < 9910 and k > 50;
                    
                             QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Seq Scan on tbl_a1 tbl_a_1
         Filter: ((i >= 990) AND (i <= 1100) AND (j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a2_j_idx on tbl_a2 tbl_a_2
         Index Cond: (j < 9910)
         Filter: ((i >= 990) AND (i <= 1100) AND (k > 50))
 SQL Hash: 1553185667, Plan Hash: -993343726
(7 rows)

強制執行資料表分割計畫

分割資料表的核准計畫會透過位置關聯強制執行。這些計畫並非分割區特有的，而且可以在原始查詢中所參照計畫以外的分割區上強制執行。這些計畫也讓您可以強制執行查詢，存取與原始核准大綱不同數目的分割區。

例如，如果核准的大綱適用於下列計畫：


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 2100 and j < 9910 and k > 50;
            
                                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Index Scan using tbl_a1_i_idx on tbl_a1 tbl_a_1
         Index Cond: ((i >= 990) AND (i <= 2100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a3_i_idx on tbl_a3 tbl_a_3
         Index Cond: ((i >= 990) AND (i <= 2100))
         Filter: ((j < 9910) AND (k > 50))   
 SQL Hash: 1553185667, Plan Hash: -993736942
(10 rows)

然後，也可以在參考 2 個、4 個或更多分割區的 SQL 查詢上強制執行此計畫。可從這些案例產生，以進行 2 和 4 分割區存取的可能計畫如下：


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 1100 and j < 9910 and k > 50;
            
                                QUERY PLAN
----------------------------------------------------------------------------------
 Append
   ->  Index Scan using tbl_a1_i_idx on tbl_a1 tbl_a_1
         Index Cond: ((i >= 990) AND (i <= 1100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 1100) AND (j < 9910) AND (k > 50))
 Note: An Approved plan was used instead of the minimum cost plan. 
 SQL Hash: 1553185667, Plan Hash: -993736942, Minimum Cost Plan Hash: -1873216041
(8 rows)


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 3100 and j < 9910 and k > 50;
            
                                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Index Scan using tbl_a1_i_idx on tbl_a1 tbl_a_1
         Index Cond: ((i >= 990) AND (i <= 3100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 3100) AND (j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a3_i_idx on tbl_a3 tbl_a_3
         Index Cond: ((i >= 990) AND (i <= 3100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a4 tbl_a_4
         Filter: ((i >= 990) AND (i <= 3100) AND (j < 9910) AND (k > 50))
 Note: An Approved plan was used instead of the minimum cost plan.
 SQL Hash: 1553185667, Plan Hash: -993736942, Minimum Cost Plan Hash: -1873216041 
(12 rows)


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 3100 and j < 9910 and k > 50;
            
                                QUERY PLAN
----------------------------------------------------------------------------------
 Append
   ->  Index Scan using tbl_a1_i_idx on tbl_a1 tbl_a_1
         Index Cond: ((i >= 990) AND (i <= 3100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 3100) AND (j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a3_i_idx on tbl_a3 tbl_a_3
         Index Cond: ((i >= 990) AND (i <= 3100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Index Scan using tbl_a4_i_idx on tbl_a4 tbl_a_4
         Index Cond: ((i >= 990) AND (i <= 3100))
         Filter: ((j < 9910) AND (k > 50))
 Note: An Approved plan was used instead of the minimum cost plan.
 SQL Hash: 1553185667, Plan Hash: -993736942, Minimum Cost Plan Hash: -1873216041
(14 rows)

請針對每個分割區考慮另一個具有不同存取方法的核准計畫：


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 2100 and j < 9910 and k > 50;
            
                                QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Index Scan using tbl_a1_i_idx on tbl_a1 tbl_a_1
         Index Cond: ((i >= 990) AND (i <= 2100))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 2100) AND (j < 9910) AND (k > 50))
   ->  Bitmap Heap Scan on tbl_a3 tbl_a_3
         Recheck Cond: ((i >= 990) AND (i <= 2100))
         Filter: ((j < 9910) AND (k > 50))
         ->  Bitmap Index Scan on tbl_a3_i_idx
               Index Cond: ((i >= 990) AND (i <= 2100))
 SQL Hash: 1553185667, Plan Hash: 2032136998
(12 rows)

在此情況下，從兩個分割區讀取的任何計畫將無法強制執行。除非來自核准計畫中的所有 (存取方法、索引名稱) 組合都可以使用，否則計畫無法強制執行。例如，下列計劃具有不同的計畫雜湊，而且在這些情況下無法強制執行核准計畫：


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 1900 and j < 9910 and k > 50;
            
                              QUERY PLAN
-------------------------------------------------------------------------
 Append
   ->  Bitmap Heap Scan on tbl_a1 tbl_a_1
         Recheck Cond: ((i >= 990) AND (i <= 1900))
         Filter: ((j < 9910) AND (k > 50))
         ->  Bitmap Index Scan on tbl_a1_i_idx
               Index Cond: ((i >= 990) AND (i <= 1900))
   ->  Bitmap Heap Scan on tbl_a2 tbl_a_2
         Recheck Cond: ((i >= 990) AND (i <= 1900))
         Filter: ((j < 9910) AND (k > 50))
         ->  Bitmap Index Scan on tbl_a2_i_idx
               Index Cond: ((i >= 990) AND (i <= 1900))
  Note: This is not an Approved plan.  No usable Approved plan was found.
  SQL Hash: 1553185667, Plan Hash: -568647260
(13 rows)


postgres=>explain (hashes true, costs false) select j, k from tbl_a where i between 990 and 1900 and j < 9910 and k > 50;
            
                              QUERY PLAN
--------------------------------------------------------------------------
 Append
   ->  Index Scan using tbl_a1_i_idx on tbl_a1 tbl_a_1
         Index Cond: ((i >= 990) AND (i <= 1900))
         Filter: ((j < 9910) AND (k > 50))
   ->  Seq Scan on tbl_a2 tbl_a_2
         Filter: ((i >= 990) AND (i <= 1900) AND (j < 9910) AND (k > 50))
 Note: This is not an Approved plan.  No usable Approved plan was found.
 SQL Hash: 1553185667, Plan Hash: -496793743
(8 rows)

命名慣例

若要讓 QPM 強制使用宣告式分割資料表的計劃，您必須遵循父項資料表、表格分割區和索引的特定命名規則：

父表格名稱 — 這些名稱必須由字母或特殊字元而不同，而不僅僅是數字。例如，對於個別的父資料表，tA，tB 和 tC 是可接受的名稱，而 t1，t2 和 t3 則不是。
個別分割區表名稱 — 同一個父系的分割區應該僅依數字而異。例如，可接受的 tA 分割區名稱可以是 tA1、tA2 或 t1A、t2A，或甚至多個數字。

任何其他差異 (字母、特殊字元) 將不保證計畫強制執行。
索引名稱 — 在分割區資料表階層中，確定所有索引都有唯一的名稱。這意味著名稱的非數字部分必須不同。例如，如果您有一個以名為索引命名tA的分區資料表tA_col1_idx1，就不能有另一個名為的索引tA_col1_idx2。但是，您可以調用索引，tA_a_col1_idx2因為名稱的非數字部分是唯一的。此規則適用於在上層資料表和個別分割表上建立的索引。

無法遵守上述命名慣例，可能會導致核准計畫強制執行失敗。下列範例說明此類失敗的強制執行：


postgres=>create table t1(i int, j int, k int, l int, m int) partition by range(i);
CREATE TABLE
postgres=>create table t1a partition of t1 for values from (0) to (1000);
CREATE TABLE
postgres=>create table t1b partition of t1 for values from (1001) to (2000);
CREATE TABLE
postgres=>SET apg_plan_mgmt.capture_plan_baselines TO 'manual';
SET
postgres=>explain (hashes true, costs false) select count(*) from t1 where i > 0;

                            QUERY PLAN
--------------------------------------------------------------------------
 Aggregate
   ->  Append
         ->  Seq Scan on t1a t1_1
               Filter: (i > 0)
         ->  Seq Scan on t1b t1_2
               Filter: (i > 0)
 SQL Hash: -1720232281, Plan Hash: -1010664377
(7 rows)


postgres=>SET apg_plan_mgmt.use_plan_baselines TO 'on';
SET
postgres=>explain (hashes true, costs false) select count(*) from t1 where i > 1000;

                            QUERY PLAN
-------------------------------------------------------------------------
 Aggregate
   ->  Seq Scan on t1b t1
         Filter: (i > 1000)
 Note: This is not an Approved plan. No usable Approved plan was found.
 SQL Hash: -1720232281, Plan Hash: 335531806
(5 rows)

即使這兩個計劃可能看起來相同，但由於子表的名稱，它們的Plan Hash值也不同。資料表名稱會因字母字元而異，而不僅僅是導致強制執行失敗的數字。

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