The documentation of DB2_FMP_COMM_HEAPSZ:
* Operating system: Windows, UNIX
* Default: 20 MB, or enough space to run 10 fenced routines (whichever is larger). On AIX®, the default is 256 MB
* This variable specifies, in 4 KB pages, the size of the pool used for fenced routine invocations, such as stored procedure or user-defined function calls. The space used by each fenced routine is twice the value of the aslheapsz configuration parameter.
If you are running a large number of fenced routines on your system, you may need to increase the value of this variable. If you are running a very small number of fenced routines, you can reduce it.
Setting this value to 0 means that no set is created, and as a result no fenced routines can be invoked. It also means that the health monitor and the automatic database maintenance functionality (such as automatic backups, statistics collection, and REORG) will be disabled since this functionality relies on the fenced routine infrastructure.
Andy