Re: R: slow seqscan after vacuum analize

Iain wrote:

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>>Yes, you are right but it wasn't the case this time, I have run the
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>explain plenty of
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>>times with same results. I think that the reason was that I made a simple
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>VACUUM,
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>>after a VACUUM FULL ANALYZE (1h!!) things are ok
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>It's reasonable to expect that a seq scan will perform faster after a full
>vacuum, as the physical size and organization of the table has been changed.
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>I wouldn't expact a plain vacuum to have any tangible affect on performance,
>for the better or for the worse..
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A plain VACUUM (without ANALYZE) will change the layout of the data
without refreshing the optimizer information, so that anything that DOES
use the optimizer will often be negatively affected; VACUUM ANALYZE
does a vacuum AND refreshes the optimizer information.

I usually run VACUUM ANALYZE on an hourly basis on our production
system, and it's fast enough and unobtrusive enough that I can't tell
that it's running (except by looking at the log, of course).

>I'd like to know more about the possibility of plain vacuums harming
>performance. This is the first I've heard of it. Vacuum full is not always
>an option in a production environment.
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