Re: Query to monitor index bloat

On Tue, 17 Jul 2018 11:03:08 +0200
Fabio Pardi <f(dot)pardi(at)portavita(dot)eu> wrote:

> On 07/17/2018 10:21 AM, Jehan-Guillaume (ioguix) de Rorthais wrote:
> > On Tue, 17 Jul 2018 10:11:50 +0200
>
> > ...and check this one: https://github.com/OPMDG/check_pgactivity/
> >
> > It uses bloat queries for tables and btree indexes Adrien Nayrat was
> > pointing earlier in this thread.
> >
> > In fact, both queries in check_pgactivity were written because the bloat
> > check in check_postgres was considering **all** fields were in **all***
> > indexes..
>
> not accurately, since it is excluding a few things.
>
> from the docs:
> 'Tables must have at least 10 pages, and indexes at least 15, before
> they can be considered by this test.'

well I agree with this. What the point of computing bloat for small objects? I
would raise this way higher.

> + you can include and exclude objects based on your taste, same as in
> check_pgactivity.
>
> The only 'drawback' of check_postgres.pl is that it checks indexes and
> tables's bloat in one go. (but: if your object's names are normalized,
> it should not be difficult to include or exclude them)
> I do not consider it a drawback, but you are free to pick your poison...

Well, again, the btree approximation is quite large in check_postgres. I would
not rely on it detect bloat quickly. **If this is still true**, as it considers
all fields are in the index, the estimated index size might be veeeeery
large compared to the real one.

But, again, this is a few years I did not digg in this query, I mmight be wrong.

> > Which is quite a large approximation...I don't know if this is still
> > the case though.
>
> While i think both tools might fit Alessandro's purpose, please note
> that check_pgactivity is **only** checking for btree indexes (which are
> the default ones, and the proven-to-get-bloated-quickly)
>
> If I were you (both), I would monitor **all** indexes (and yes! tables
> too), since one day you might realize it was actually a good idea to do so.

I agree, we should monitor all indexes. If you have some formula to quickly
estimate ideal size of a GIN, GiST, hash or sp-gist indexes, please share. But,
unfortunately, as far as I know, this is way more complex than just summing the
average size of the fields in the index :/