You can identify native heap exhaustion by monitoring the svmon snapshot output
Each segment is 256 MB of space, which corresponds to 65535 pages. (Inuse is measured in 4 KB pages.)
If each of the segments has approximately 65535 Inuse pages, the process is suffering from native heap exhaustion. At this point, extending the native heap size might solve the problem, but you should investigate the memory usage profile to ensure that you do not have a leak.
If DB2® is running on your AIX® system, you can change the application code to use the "net" (thin client) drivers and, in the case of WebSphere® MQ you can use the "client" (out of process) drivers.