Greg Smith <greg@2ndquadrant.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
