This article explains why heap utilization may appear high on SRX Series devices when checking forwarding process memory usage with the show chassis forwarding command.

When monitoring the output of "show chassis forwarding" on an SRX device, administrators may observe high heap utilization values (for example, above 80%).

Example output:

> show chassis forwarding

FWDD status:

 State                Online

 Microkernel CPU utilization     0 percent

 Real-time threads CPU utilization  0 percent

 Heap utilization          83 percent

 Buffer utilization         90 percent

 Uptime:               18 hours, 17 minutes, 19 seconds

High heap utilization on SRX is expected behavior and does not necessarily indicate a memory leak or a fault.

The flow module pre-allocates hundreds of MBs for session tables (and other data structures). This allocation gives a performance improvement because memory does not have to allocate from the free memory pool at run time.

As a result, heap utilization percentages may appear consistently high, even under normal operation.