Query to monitor index bloat

On 07/16/2018 05:16 PM, Alessandro Aste wrote:

Hello,  I am trying to put togheter a query to monitor the index bloat
for a database I maintain.
Is there a "SQL" way to obtain  bloated index ? I googled around but I
found nothing working.

I'm currently running 9.6 but I'm looking for something compatible with
version 10 too.

Thank you very much in advance,

Alessandro.

Hello,

You should look at : https://github.com/ioguix/pgsql-bloat-estimation

Regards,

Thanks much, I'll check that out. I see the queries are 3 years old so I'm
wondering if they still work for 9.6.x or 10

Il lun 16 lug 2018, 17:44 Adrien NAYRAT <adrien.nayrat@anayrat.info> ha
scritto:

On 07/16/2018 11:50 PM, Alessandro Aste wrote:

Thanks much, I'll check that out.  I see the queries are 3 years old so I'm
wondering if they still work for 9.6.x or 10

AFAIK they work. You can try yourself by comparing bloated table/index size
before and after vacuum full or reindex ;)

If you monitor using nagios (or if you want to make a wrapper around it):

https://bucardo.org/check_postgres/check_postgres.pl.html#bloat

works like a charm.

regards,

fabio pardi

On Tue, 17 Jul 2018 10:11:50 +0200
Fabio Pardi <f.pardi@portavita.eu> wrote:

If you monitor using nagios (or if you want to make a wrapper around it):

https://bucardo.org/check_postgres/check_postgres.pl.html#bloat

...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...Which is quite a large approximation...I don't know if this is still
the case though.

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.'

+ 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...

.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.

regards,

fabio pardi

On Tue, 17 Jul 2018 11:03:08 +0200
Fabio Pardi <f.pardi@portavita.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 :/

you have your points, my friend.