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更新时间：2024-05-20 GMT+08:00
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PBE动态剪枝

PBE动态剪枝支持范围如下所示：
  1. 支持分区级别：一级分区、二级分区。
  2. 支持分区类型：范围分区、间隔分区、哈希分区、列表分区。
  3. 支持表达式类型：比较表达式（<，<=，=，>=，>）、逻辑表达式、数组表达式。
  4. 支持部分隐式类型转换和函数：对于类型可以相互转换的场景和immutable函数可以支持PBE动态剪枝
  • PBE动态剪枝支持表达式、隐式转换、immutable函数，stable函数，不支持子查询表达式和volatile函数。对于stable函数，如to_timestamp等类型转换函数，可能会受GUC参数变化，影响剪枝结果。为了保持性能优化，此情况可以通过analyze表重新生成gplan解决。
  • 由于PBE动态剪枝是基于generic plan的剪枝，所以判断语句是否能PBE动态剪枝时，需要设置参数 plan_cache_mode = 'force_generic_plan'，排除custom plan的干扰。
  • 对于二级分区表指定一级分区的查询语句，不支持对二级分区键的过滤条件进一步剪枝。
  • PBE动态剪枝支持的典型场景具体示例如下：
    1. 比较表达式 
      --创建分区表
gaussdb=# CREATE TABLE t1 (c1 int, c2 int)
PARTITION BY RANGE (c1)
(
    PARTITION p1 VALUES LESS THAN(10),
    PARTITION p2 VALUES LESS THAN(20),
    PARTITION p3 VALUES LESS THAN(MAXVALUE)
);
--设置参数
gaussdb=# set plan_cache_mode = 'force_generic_plan';

gaussdb=# PREPARE p1(int) AS SELECT * FROM t1 WHERE c1 = $1;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p1(1);
               QUERY PLAN                
-----------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 = $1)
         Selected Partitions:  1 (pbe-pruning)
(7 rows)

gaussdb=# PREPARE p2(int) AS SELECT * FROM t1 WHERE c1 < $1;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p2(1);
               QUERY PLAN                
-----------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 < $1)
         Selected Partitions:  1 (pbe-pruning)
(7 rows)

gaussdb=# PREPARE p3(int) AS SELECT * FROM t1 WHERE c1 > $1;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p3(1);
               QUERY PLAN                
-----------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 > $1)
         Selected Partitions:  1..3 (pbe-pruning)
(7 rows)
    2. 逻辑表达式 
      gaussdb=# PREPARE p5(INT, INT) AS SELECT * FROM t1 WHERE c1 = $1 AND c2 = $2;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p5(1, 2);
                   QUERY PLAN                    
-------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: ((t1.c1 = $1) AND (t1.c2 = $2))
         Selected Partitions:  1 (pbe-pruning)
(7 rows)

gaussdb=# PREPARE p6(INT, INT) AS SELECT * FROM t1 WHERE c1 = $1 OR c2 = $2;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p6(1, 2);
                   QUERY PLAN                   
------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: ((t1.c1 = $1) OR (t1.c2 = $2))
         Selected Partitions:  1..3 (pbe-pruning)
(7 rows)
gaussdb=# PREPARE p7(INT) AS SELECT * FROM t1 WHERE NOT c1 = $1;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) execute p7(1);
               QUERY PLAN                
-----------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 <> $1)
         Selected Partitions:  1..3 (pbe-pruning)
(7 rows)
    3. 数组表达式 
      gaussdb=# PREPARE p8(INT, INT, INT) AS SELECT * FROM t1 WHERE c1 IN ($1, $2, $3);
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p8(1, 2, 3);
                    QUERY PLAN                     
---------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 = ANY (ARRAY[$1, $2, $3]))
         Selected Partitions:  1 (pbe-pruning)
(7 rows)
gaussdb=# PREPARE p9(INT, INT, INT) AS SELECT * FROM t1 WHERE c1 NOT IN ($1, $2, $3);
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p9(1, 2, 3);
                     QUERY PLAN                     
----------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 <> ALL (ARRAY[$1, $2, $3]))
         Selected Partitions:  1..3 (pbe-pruning)
(7 rows)
gaussdb=# PREPARE p10(INT, INT, INT) AS SELECT * FROM t1 WHERE c1 = ALL(ARRAY[$1, $2, $3]);
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p10(1, 2, 3);
                    QUERY PLAN                     
---------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 = ALL (ARRAY[$1, $2, $3]))
         Selected Partitions:  NONE (pbe-pruning)
(7 rows)
gaussdb=# PREPARE p11(INT, INT, INT) AS SELECT * FROM t1 WHERE c1 = ANY(ARRAY[$1, $2, $3]);
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p11(1, 2, 3);
                    QUERY PLAN                     
---------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 = ANY (ARRAY[$1, $2, $3]))
         Selected Partitions:  1 (pbe-pruning)
(7 rows)
gaussdb=# PREPARE p12(INT, INT, INT) AS SELECT * FROM t1 WHERE c1 = SOME(ARRAY[$1, $2, $3]);
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p12(1, 2, 3);
                    QUERY PLAN                     
---------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 = ANY (ARRAY[$1, $2, $3]))
         Selected Partitions:  1 (pbe-pruning)
(7 rows)
    4. 类型转换触发隐式转换 
      gaussdb=# set plan_cache_mode = 'force_generic_plan';
gaussdb=# PREPARE p13(TEXT) AS SELECT * FROM t1 WHERE c1 = $1;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p13('12');
                    QUERY PLAN
--------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 = ($1)::bigint)
         Selected Partitions:  2 (pbe-pruning)
(7 rows)
    5. immutable函数 
      gaussdb=# PREPARE p14(TEXT) AS SELECT * FROM t1 WHERE c1 = LENGTHB($1);
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p14('hello');
                    QUERY PLAN
--------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: PART
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: (t1.c1 = lengthb($1))
         Selected Partitions:  1 (pbe-pruning)
(7 rows)
  • PBE动态剪枝不支持的典型场景具体示例如下：
    1. 子查询表达式 
      gaussdb=# PREPARE p15(INT) AS SELECT * FROM t1 WHERE c1 = ALL(SELECT c2 FROM t1 WHERE c1 > $1);
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p15(1);
                         QUERY PLAN                          
-------------------------------------------------------------
 Partition Iterator
   Output: public.t1.c1, public.t1.c2
   Iterations: 3
   ->  Partitioned Seq Scan on public.t1
         Output: public.t1.c1, public.t1.c2
         Filter: (SubPlan 1)
         Selected Partitions:  1..3
(7 rows)
    2. 类型转换无法直接触发隐式转换 
      gaussdb=# PREPARE p16(name) AS SELECT * FROM t1 WHERE c1 = $1;
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p16('12');
                  QUERY PLAN
----------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: 3
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: ((t1.c1)::text = ($1)::text)
         Selected Partitions:  1..3
(7 rows)
    3. stable/volatile函数 
      gaussdb=# create sequence seq;
gaussdb=# PREPARE p17(TEXT) AS SELECT * FROM t1 WHERE c1 = currval($1);--volatile函数不支持剪枝
PREPARE
gaussdb=# EXPLAIN (VERBOSE ON, COSTS OFF) EXECUTE p17('seq');
                          QUERY PLAN
--------------------------------------------------------------
 Partition Iterator
   Output: c1, c2
   Iterations: 3
   ->  Partitioned Seq Scan on public.t1
         Output: c1, c2
         Filter: ((t1.c1)::numeric = currval(($1)::regclass))
         Selected Partitions:  1..3
(7 rows)

--清理示例
gaussdb=# DROP TABLE t1;
父主题： 分区表动态剪枝