Allocates segment host memory per query. The amount of memory allocated with this parameter cannot exceed max_statement_mem or the memory limit on the resource queue through which the query was submitted. When gp_resqueue_memory_policy =auto, statement_mem and resource queue memory limits control query memory usage.

If additional memory is required for a query, temporary spill files on disk are used.

This calculation can be used to estimate a reasonable value for a wide variety of situations.

( gp_vmem_protect_limitGB * .9 ) / max_expected_concurrent_queries

With the gp_vmem_protect_limit set to 8192MB (8GB) and assuming a maximum of 40 concurrent queries with a 10% buffer

(8GB * .9) / 40 = .18GB = 184MB