November, 2015

Impact of Lack of Memory on CPU Usage

One of our customers asked me to analyze the performance of the IBM i LPAR that hosts their primary Domino and Sametime servers as they had some concerns.  The LPAR hosts 5 Domino servers (Mail, Application, Administration, Sametime, and Dev/Test) along with the Sametime DB2, SSC, Proxy, and Meeting servers.

My analysis revealed quite high CPU utilization at times, in addition to faulting issues in the *BASE memory pool. The *BASE memory pool is pool 2, where all of the Domino and WAS-based Sametime servers run by default. Some of the Domino servers (Administration, Dev/Test, and Domino Sametime) had previously been moved to separate memory pools.

To determine which servers were causing the bulk of the faulting the *BASE pool, I created a query against the QAPMJOBL performance monitor database file.  The two top faulters were the Mail and Application servers.  I made a recommendation to move the Mail and Application servers to their own memory pool, allocating 36 GB of memory to each memory pool as a starting point.  I also recommended moving the Administration, Dev/Test, and Domino Sametime server back to the *BASE memory pool. This quite dramatically changed the memory allocations on the server.

The table below shows the memory allocations as they were when I performed my analysis.

Memory Pool Allocations Prior

This next table shows memory allocations after implementing my recommendations.

Memory Pool Allocations After

My memory tuning recommendations were implemented on October 25th.  The impact on CPU utilization was quite dramatic as shown in the graphic below.

CPU Utilization After Memory Pool Adjustment

Proper memory allocation is key for the best Domino performance!