Re: Minimal logical decoding on standbys

On Tue, 16 Jul 2019 at 22:56, Andres Freund <andres@anarazel.de> wrote:
>
> Hi,
>
> On 2019-07-12 14:53:21 +0530, tushar wrote:
> > On 07/10/2019 05:12 PM, Amit Khandekar wrote:
> > > All right. Will do that in the next patch set. For now, I have quickly
> > > done the below changes in a single patch again (attached), in order to
> > > get early comments if any.
> > Thanks Amit for your patch. i am able to see 1 issues  on Standby server -
> > (where  logical replication slot created ) ,
> > a)size of  pg_wal folder  is NOT decreasing even after firing get_changes
> > function
>
> Even after calling pg_logical_slot_get_changes() multiple times? What
> does
> SELECT * FROM pg_replication_slots; before and after multiple calls return?
>
> Does manually forcing a checkpoint with CHECKPOINT; first on the primary
> and then the standby "fix" the issue?

I independently tried to reproduce this issue on my machine yesterday.
I observed that :
sometimes, the files get cleaned up after two or more
pg_logical_slot_get_changes().
Sometimes, I have to restart the server to see the pg_wal files cleaned up.
This happens more or less the same even for logical slot on *primary*.

Will investigate further with Tushar.


>
>
> > b)pg_wal files are not recycling  and every time it is creating new files
> > after firing get_changes function
>
> I'm not sure what you mean by this. Are you saying that
> pg_logical_slot_get_changes() causes WAL to be written?
>
> Greetings,
>
> Andres Freund



-- 
Thanks,
-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company