本站中文解释
PARALLEL_EXECUTION_MESSAGE_SIZE参数用于控制表并行执行时 Oracle 给出的消息大小, 其影响的是以下两个因素
1. 表的并行度：如果这个值太低，将会影响表的并行度，导致表并行化效率下降。
2. 返回的内存大小：根据这个参数的设置，Oracle将给出的消息内容来划定内存的大小，内存的大小不能超过这个值，否则内存侧写过程会因内存不足而报错。
Oracle 设置这个参数的普遍建议把它设置在8MB以内，另外如果表中只包含小数据类型，建议把它设置在1MB以内。
在设置这个参数之前，首先要根据表的特性先去设置表及其依赖表的并行度。在设置参数之后，可以通过执行 v$pq_sysstat 视图来检查参数的设置值，如果发现有任何违反建议的设置值，可以调整参数的值来取得最优的效果。
官方英文解释
PARALLEL_EXECUTION_MESSAGE_SIZE specifies the size of messages used for parallel execution (formerly referred to as parallel query, PDML, Parallel Recovery, replication).
| Property | Description |
|---|---|
| Parameter type |
Integer |
| Default value |
Operating system-dependent |
| Modifiable |
No |
| Modifiable in a PDB |
No |
| Range of values |
Minimum: 2148 Maximum: 65536, but some operating systems may have a smaller value |
| Basic |
No |
| Oracle RAC |
Multiple instances must have the same value. |
On most platforms, the default value is as follows:
-
16384bytes ifCOMPATIBLEis set to11.2.0or higher -
2148bytes ifCOMPATIBLEis less than11.2.0
The default value is adequate for most applications. Larger values require a larger shared pool. Larger values result in better performance at the cost of higher memory use. For this reason, replication gets no benefit from increasing the size.
See Also:
Oracle Database VLDB and
Partitioning Guide to learn how this parameter affects memory consumption for parallel operations, including parallel execution