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
Data in Trouble? Get it in Treble! http://BlueTreble.com
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