Introduced in release: 7.0.5
dbregionmax Message Store option sets the maximum amount of memory to be used by shared structures in the mboxlist environment region. These are the structures used to coordinate access to the environment other than mutexes and those in the page cache. Values in the range 33554432-536870912 (from 32*1024*1024 to 512*1024*1024) are allowed, with the default being 33554432.
The default value is: 33554432