Re: Auto-analyse on insert operations

Le 04/11/2015 14:55, Bill Moran a écrit :
> On Wed, 4 Nov 2015 14:32:37 +0100
> Bertrand Roos <bertrand(dot)roos(at)areal(dot)fr> wrote:
>> I try to configure auto-analyse task with postgresql 9.4.
>> I have the following configuration (default configuration):
>> track_counts = on
>> autovacuum = on
>> log_autovacuum_min_duration = -1
>> autovacuum_max_workers = 3
>> autovacuum_naptime = 300s
>> autovacuum_vacuum_threshold = 50
>> autovacuum_analyze_threshold = 50
>> autovacuum_vacuum_scale_factor = 0.2
>> autovacuum_analyze_scale_factor = 0.2
>> autovacuum_freeze_max_age = 200000000
>> autovacuum_multixact_freeze_max_age = 400000000
>> autovacuum_vacuum_cost_delay = 20ms
>> autovacuum_vacuum_cost_limit = -1
>>
>> With this configuration, I can observe that some tables are
>> auto-analysed, but some others are not. Even if there are millions of
>> insert operations on an empty table (all tables are in cluster mode).
>> In fact it seems that tables with update operations are the only ones
>> that are auto-analysed.
>> I'm quite suprised because the documentation says that daemon check the
>> count of insert, update and delete operations.
>> What could it be the reason ? Why tables which have only update
>> operation, aren't analysed ?
>> Are update operations really taken into account ?
> Given that autoanalyze is pretty critical to the way the system functions,
> it's unlikely that it just doesn't work (someone else would have noticed).
>
> A more likely scenario is that you've found some extremely obscure edge
> case. If that's the case, you're going to have to give very specific
> details as to how you're testing it before anyone is liable to be able
> to help you.
>
> I get the impression that you're somewhat new to Postgres, in which case
> it's very likely that the problem is that you're not testing the situation
> correctly. In that case, we're going to need specific details on how you're
> observing that tables are or are not being analysed.
>
> As a wild-guess theory: the process that does the analyze only wakes up
> to check tables every 5 minutes (based on the config you show) ... so are
> you doing the inserts then checking the table without leaving enough time
> in between for the system to wake up and notice the change?
>
Thanks for your answer Bill.
Indeed, I'm pretty new to Postgres and I don't exclude that I'm doing
something wrong. But I did my test on a more than 1 day duration, so
it's not an issue of autovacuum_naptime (I insert 760 lignes each 30
seconds during 36 hours).
I can't give all the details of this test because it is to complicated
with triggers and partman (and your objective is not to solve
configuration issues of others).

In fact, I was telling the question because I have read on some forums
that the auto vacuum deamon only count dead tuple so only update and
delete operations can cause the scheduling of auto-analyse.
So if it's the case it perfectly explain why my test case doesn't work.
But in the other hand the documentation says that delete, update and
insert operations are counted.
Is it an know issue that insert operations are not counted for the
trigger of auto-analyse ?

If it's not, I can try to reproduce this weird behaviour with a simpler
test and give you all the details of the test.

Bertrand