Kingbasees plug-in KDB of Jincang database_ exists_ expand

1.  The plugin is introduced

kdb_exists_expand Plug ins are used to optimize EXISTS Sub Links , Generate more efficient execution plans .

For the existence of EXISTS Sub connected SQL sentence , If meet ：

1. EXISTS Child link is SELECT Query statement of type

2. EXISTS Sub links are OR Conditions , Such as ：

• SELECT * from a WHERE EXISTS (SELECT 1 from e cond1 OR cond2);

• Among them cond1 The query condition of is related to the table queried in the sub link ,cond2 The query condition of is independent of the table queried in the sub link , Such as ：

SELECT * from a WHERE EXISTS (SELECT 1 from e WHERE e.id =1 OR a.name = null);

• among cond1 by e.id =1, With tables in child links e relevant

• among cond2 by a.name = null, With tables in child links e Unrelated

Then the plug-in will EXISTS Improve and optimize the unrelated conditions of sub links , Can improve SQL Query execution efficiency .

2.  Add plug-ins

In the use of kdb_exists_expand Before , You need to add it to kingbase.conf Of documents shared_preload_libraries in , And restart the database .

shared_preload_libraries = 'kdb_exists_expand' # (change requires restart)

3.  Parameter configuration

kdb_exists_expand.enable

exists Sub link optimization switch ,boolean Type data , On by default .

4.  Example

After starting this function , It was supposed to be a Semi join Implementation plan of , It has been changed into two parallel sub plans SubPlan 2 and SubPlan 3 To execute , and SubPlan3 It's the one that comes up Exists Sub Links .

# explain (costs false) select p.parameter_value from sheet_parameter p join dep_b001 e on
exists (
    select 1 from dep_b001 e
    where e.dep_id in ('b8703c00fb4973aaa1723f95475dfa')
      and p.parameter_value like e.tree_level_code || '%'
      or p.parameter_value is null);

QUERY PLAN
-----------------------------------------------------------------------
 Limit
   ->  Result
         ->  Sort
               Sort Key: b.sheet_no, d.ordinal
               ->  Hash Left Join
                     Hash Cond: (c.sheet_id = p.sheet_id)
                     Filter: ((SubPlan 2) OR (SubPlan 3))
                     ->  Nested Loop Left Join
                           Join Filter: (d.design_id = b.id)
                           ->  Nested Loop
                                 Join Filter: (d.id = c.sheet_id)
                                 ->  Seq Scan on sheet d
                                 ->  Materialize
                                       ->  Seq Scan on sheet_sheet_category c
                                             Filter: (category_id = '\x7a3ca091e24459a4f8c23eb10197f7'::bytea)
                           ->  Seq Scan on sheet_design b
                     ->  Hash
                           ->  Seq Scan on sheet_parameter p
                     SubPlan 2
                       ->  Seq Scan on dep_b001 e
                             Filter: (((dep_id)::text = 'b8703c00fb4973aaa1723f95475dfa'::text) AND ((p.parameter_value)::text ~~ ((tree_level_code)::text || '%'::text)))
                     SubPlan 3
                       ->  Result
                             One-Time Filter: (p.parameter_value IS NULL)
                             ->  Seq Scan on dep_b001 e_1
         SubPlan 1
           ->  Aggregate
                 ->  Seq Scan on sheet_data a
                       Filter: ((sheet_id = d.id) AND (status = '0'::numeric))
(29 rows)

5.  Uninstall plugins

modify kingbase.conf In file  shared_preload_libraries  Restart the database after parameters .

shared_preload_libraries = ''