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The Parallel servers communicate among themselves and with the Query Coordinator by passing messages via memory buffers.
If you execute a lot of large operations in parallel pa, it’s advisable to reduce the messaging latency by increasing the parallel_execution_message_size (the size of the buffers).
By default the message size is 2K. Ideally you should increase it to 16k (16384).
However, a larger value for parallel_execution_message_size will increase the memory requirement for the shared pool so if you increase it from 2K to 16K your parallel server memory requirement will be 8 X more.