Re: Remove autovacuum GUC?

On 10/20/16 11:50 PM, Craig Ringer wrote:
> Personally what I think is needed here is to make monitoring and bloat
> visibility not completely suck. So we can warn users if tables haven't
> been vac'd in ages and have recent churn. And so they can easily SELECT
> a view to get bloat estimates with an estimate of how much drift there
> could've been since last vacuum.

+10. I've seen people spend a bunch of time screwing around with the 2
major "bloat queries", both of which have some issues. And there is *no*
way to actually quantify whether autovac is keeping up with things or not.

> Users turn off vacuum because they cannot see that it is doing anything
> except wasting I/O and cpu. So:
>
> * A TL;DR in the docs saying what vac does and why not to turn it off.
> In particular warning that turning autovac off will make a slow SB get
> slower even though it seems to help at first.

IMHO we should also suggest that for users that have periods of lower
activity that they run a manual vacuum. That reduces the odds of autovac
ruining your day unexpectedly, as well as allowing it to to focus on
high-velocity tables that need more vacuuming and not on huge tables
that just happened to surpass their threshold during a site busy period.

> * A comment in the conf file with the same TL;DR. Comments are free,
> let's use a few lines.
>
> * Warn on startup when autovac is off?

Well, I suspect that someone who thinks autovac=off is a good idea
probably doesn't monitor their logs either, but it wouldn't hurt.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
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