Product Limitation: APM SiteMinder WebAgent extension fails to monitor SiteMinder Web Access Manager Web Agent metrics for multiple web server instances
A shared memory segment is critical for collecting metric data from a SiteMinder Web Agent using the APM WebAgent extension.
The Apache Portable Runtime (APR) library global mutex is used to serialize access to the shared memory segment. In a typical environment, the SiteMinder Web Agent uses the extension to execute Introscope API calls and place metrics into the shared memory segment using APR.
When monitoring is configured for more than one web server instance on the same server, it is observed that the locking around this shared memory is not functioning. This because the APR global mutex fails to work across independent processes.
Due to the above limitation, monitoring multiple web server instances can lead to a shared memory corruption with the following consequences:
1. After the corruption one might see the monitored processes (and threads if any spawned) of the Web Agent hung.
2. The following observations from the IntroscopeAPI.log, when debug mode is set:
a. A warning message - warn: Metric table overflow: <some large number> elements
b. Junk characters in the metric name e.g.
Iscope:07/10/12(16:02:50):07865:7440064 DEBUG - GetMetricFromShm:(n,t): __¢ÿÄ, PerInterval Counter
3. Eventually a crash will occur on the SiteMinder Web Agent.
The issue is observed across all variants of Apache web servers on Unix/Linux platforms.