From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Rick <richard(dot)branton(at)ca(dot)com>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: autovacuum strategy / parameters |
Date: | 2010-05-01 17:25:40 |
Message-ID: | 5266.1272734740@sss.pgh.pa.us |
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Lists: | pgsql-performance |
Greg Smith <greg(at)2ndquadrant(dot)com> writes:
> If anything, I'd expect people to want to increase how often it runs,
> for tables where much less than 20% dead is a problem. The most common
> situation I've seen where that's the case is when you have a hotspot of
> heavily updated rows in a large table, and this may match some of the
> situations that Robert was alluding to seeing. Let's say you have a big
> table where 0.5% of the users each update their respective records
> heavily, averaging 30 times each. That's only going to result in 15%
> dead rows, so no autovacuum. But latency for those users will suffer
> greatly, because they might have to do lots of seeking around to get
> their little slice of the data.
With a little luck, HOT will alleviate that case, since HOT updates can
be reclaimed without running vacuum per se. I agree there's a risk
there though.
Now that partial vacuum is available, it'd be a real good thing to
revisit these numbers.
regards, tom lane
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