From: | Steve Crawford <scrawford(at)pinpointresearch(dot)com> |
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To: | Alexander Staubo <alex(at)purefiction(dot)net> |
Cc: | Tom Allison <tom(at)tacocat(dot)net>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: When should I worry? |
Date: | 2007-06-11 17:08:19 |
Message-ID: | 466D8183.20506@pinpointresearch.com |
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Lists: | pgsql-general |
Alexander Staubo wrote:
> ....
> For the monitoring, however, you can log your queries along with
> timings and timestamps, and copy them into a tool like R to
> statistically analyze your performance over time. You will be able to
> predict the point at which your system will be too slow to use, if
> indeed the performance degradation is expontential.
> ...
In my experience the more common situation is to "go off a cliff."
Everything hums along fine and the increases in table-size and user-base
have very little impact on your response times. Then suddenly you run
out of some resource (usually memory first).You hit swap and as your
few-millisecond query takes seconds or minutes your request queue backs
up, new connections are denied and everything goes downhill fast.
I think that keeping an eye on system resource trends via sar or similar
is more likely to provide the desired warnings of "sudden dropoff ahead".
Cheers,
Steve
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