PARALLEL_EXECUTION_MESSAGE_SIZE

Property	Description
Parameter type	Integer
Default value	Operating system-dependent
Modifiable	No
Range of values	Minimum: 2148 Maximum: 32768, but some operating systems may have a smaller value
Oracle RAC	Multiple instances must have the same value.

PARALLEL_EXECUTION_MESSAGE_SIZE specifies the size of messages used for parallel execution (formerly referred to as parallel query, PDML, Parallel Recovery, replication).

On most platforms, the default value is as follows:

16384 bytes if COMPATIBLE is set to 11.2.0 or higher
4096 bytes if COMPATIBLE is less than 11.2.0 and PARALLEL_AUTOMATIC_TUNING is set to true
2148 bytes if COMPATIBLE is less than 11.2.0 and PARALLEL_AUTOMATIC_TUNING is set to false

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.

Note:

When PARALLEL_AUTOMATIC_TUNING is set to TRUE, message buffers are allocated out of the large pool. In this case, the default is generally higher. Note that the PARALLEL_AUTOMATIC_TUNING parameter has been deprecated.