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本站中文解释
BITMAP_MERGE_AREA_SIZE 参数控制带有位图的SQL语句的合并区的大小，比如用于AND条件的查询 。
这个参数默认值是1048576(1M)，最大值取决于你实例参数值PGA_AGGREGATE_TARGET 的大小。你也可以重新设置这个参数，但是最好将其设置为不超过PGA_AGGREGATE_TARGET的50%左右。
它也可以用于创造和索引不匹配情况，尤其是如果这个参数不足以容纳所有位图组。
正确设置方法：
首先需要查看PGA_AGGREGATE_TARGET 的大小，然后以该参数的一半左右作为BITMAP_MERGE_AREA_SIZE的值，设置时的命令为alter system set BITMAP_MERGE_AREA_SIZE =；单位为字节。最后commit。
官方英文解释
BITMAP_MERGE_AREA_SIZE specifies the amount of memory Oracle uses to merge bitmaps retrieved from a range scan of the index.
| Property | Description |
|---|---|
|
Parameter type |
Integer |
|
Default value |
|
|
Modifiable |
No |
|
Modifiable in a PDB |
Yes |
|
Range of values |
Operating system-dependent |
|
Basic |
No |
Note:
Oracle does not recommend using the BITMAP_MERGE_AREA_SIZE parameter unless the instance is configured with the shared server option. Oracle recommends that you enable automatic sizing of SQL working areas by setting PGA_AGGREGATE_TARGET instead. BITMAP_MERGE_AREA_SIZE is retained for backward compatibility.
BITMAP_MERGE_AREA_SIZE is relevant only for systems containing bitmap indexes. A larger value usually improves performance, because the bitmap segments must be sorted before being merged into a single bitmap.
See Also:
Oracle Database SQL Tuning
Guide for more information on using bitmap indexes for performance
