Re: vacuumdb idle processes

Hi,

I tested this scenario and it seems if vacuumdb is started with multiple
jobs and one of the jobs doesn't complete due to a lock or whatever reason,
other jobs will stay idle and don't release the connection until the stuck
job is finished.

For my understanding, why do we need this behaviour?

Thanks and Regards,
Nikhil

On Sat, Jun 12, 2021 at 12:34 PM Nikhil Shetty <nikhil(dot)dba04(at)gmail(dot)com>
wrote:

> Hi Tom,
>
> Apparently not all that well, if it failed to keep us out of an
>> autovacuum-to-prevent-wraparound situation. I suppose you had autovacuum
>> disabled because you thought this lashup was sufficient?
>
>
> No, autovacuum was enabled but seems it was not able to catch up with the
> amount of transaction or it might have been delayed due to postgres
> favouring other txns that conflict -- Need to check this though
>
> Perhaps this is the last remaining table so vacuumdb has nothing
>> else for them to do.
>>
>
> Does this mean vacuumdb will release all db connections(jobs - 8 in this
> case) only after all connections have performed their vacuum and then
> disconnected? Even if one is pending the others will be still connected but
> in idle state? Is my understanding correct?
>
> Thanks and Regards,
> Nikhil
>
> On Sat, Jun 12, 2021 at 12:03 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Nikhil Shetty <nikhil(dot)dba04(at)gmail(dot)com> writes:
>> > I have done a setup to run vacuumdb with 8 parallel jobs daily. It has
>> been
>> > running quite well.
>>
>> Apparently not all that well, if it failed to keep us out of an
>> autovacuum-to-prevent-wraparound situation. I suppose you had autovacuum
>> disabled because you thought this lashup was sufficient?
>>
>> > Just today I saw there is an aggressive autovacuum process running(to
>> > prevent wraparound) on one of the table. vacuumdb which started later
>> > spawned the 8 connections. One connection (doing vacuum on the table on
>> > which an aggressive autovacuum is running) is waiting for "autovacuum(to
>> > prevent wraparound)" to complete while the other 7 connections are just
>> > sitting idle.
>>
>> > I am okay that one connection is waiting since an aggressive autovacuum
>> is
>> > running on that table but how come other connections have not released
>> the
>> > sesion yet? Any reason for this?
>>
>> Perhaps this is the last remaining table so vacuumdb has nothing
>> else for them to do.
>>
>> regards, tom lane
>>
>