Re: Query to monitor index bloat

you have your points, my friend.

On 07/17/2018 11:23 AM, Jehan-Guillaume (ioguix) de Rorthais wrote:
> 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 :/
>