Bitmap Scan Hints

Description

These hints generate a bitmap scan path by using the specified index on the target table. The path that meets the hint requirement is selected from the paths that can be generated by the optimizer.

Syntax

[no] bitmapscan([@queryblock] table [index_list])

Parameters

• no indicates that the specified hint will not be used for a join.

• For details about @queryblock, see Hint for Specifying the Query Block Where the Hint Is Located. This parameter can be omitted, indicating that it takes effect in the current query block.
• table indicates the target table of the bitmap scan.
• index_list indicates the index used by the bitmap scan.

Example

gaussdb=# explain(costs off)  select /*+ BitmapScan(t1 it1 it3)*/* from t1 where  (t1.c1 = 5 or t1.c2=6) or (t1.c3=3 or t1.c2=7);
                           QUERY PLAN                           
----------------------------------------------------------------
 Bitmap Heap Scan on t1
   Recheck Cond: ((c1 = 5) OR (c2 = 6) OR (c3 = 3) OR (c2 = 7))
   ->  BitmapOr
         ->  Bitmap Index Scan on it1
               Index Cond: (c1 = 5)
         ->  Bitmap Index Scan on it3
               Index Cond: (c2 = 6)
         ->  Bitmap Index Scan on it3
               Index Cond: (c3 = 3)
         ->  Bitmap Index Scan on it3
               Index Cond: (c2 = 7)
(11 rows)