Tuesday, November 3, 2009

Performance Counter - Got Enough RAM?

The Memory\Pages/sec counter indicates the number of paging operations to disk during the measuring interval, and this is the primary counter to watch for indication of possible insufficient RAM to meet your server's needs. A good idea here is to configure a perfmon alert that triggers when the number of pages per second exceeds 50 per paging disk on your system. Another key counter to watch here is Memory\Available Bytes, and if this counter is greater than 10% of the actual RAM in your machine then you probably have more than enough RAM and don't need to worry.

You should do two things with the Memory\Available Bytes counter: create a performance log for this counter and monitor it regularly to see if any downward trend develops, and set an alert to trigger if it drops below 2% of the installed RAM. If a downward trend does develop, you can monitor Process(instance)\Working Set for each process instance to determine which process is consuming larger and larger amounts of RAM. Process(instance)\Working Set measures the size of the working set for each process, which indicates the number of allocated pages the process can address without generating a page fault. A related counter is Memory\Cache Bytes, which measures the working set for the system i.e. the number of allocated pages kernel threads can address without generating a page fault.

Finally, another corroborating indicator of insufficient RAM is Memory\Transition Faults/sec, which measures how often recently trimmed page on the standby list are re-referenced. If this counter slowly starts to rise over time then it could also indicating you're reaching a point where you no longer have enough RAM for your server to function well

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