VM_OUT_BYTES Value from AWR and its Meaning
Last updated on MARCH 16, 2017
Applies to:Oracle Database - Enterprise Edition - Version 188.8.131.52 and later
Information in this document applies to any platform.
Problems with paging or swapping are often hard to spot because there is no "Top Ten Wait" symptom. The problem can manifest as concurrency problems of various kinds and is often seen with intermittent hangs or periods of slowness. High rates or latch misses and "sleeps" are often seen and timeouts can occur for remotely connecting sessions or key processes on the database. VM_OUT_BYTES can occasionally be non-zero and NOT be a problem. This is the case for older AIX systems (where VM_OUT_BYTES is misreported due to <Document 11801934.8> WRONG PAGE-IN AND PAGE-OUT OS VM STATS IN AIX.) If the value of VM_OUT_BYTES is non-zero but is a small percentage of main memory it might be an acceptable amount of paging.
In the Operating System Statistics section of the AWR you will see a high use of VM_OUT_BYTES:
Another symptom which you may notice is that the total of all waits in the top 10 does not add up to 100% or anywhere near 100%.
This is a typical example:
In this case we see that the top waits add up to 48.8 instead of 100%.
The following changes may have occurred:
1. workload might have increased
2. some process was using more PGA than usual
3. new application was added to the system
4. excessive use of Shared Pool has caused the shared pool to expand
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