Re: max_slot_wal_keep_size and wal_keep_segments

At Mon, 13 Jul 2020 14:14:30 +0900, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote in
>
>
> On 2020/07/09 13:47, Kyotaro Horiguchi wrote:
> > At Thu, 9 Jul 2020 00:37:57 +0900, Fujii Masao
> > <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote in
> >>
> >>
> >> On 2020/07/02 2:18, David Steele wrote:
> >>> On 7/1/20 10:54 AM, Alvaro Herrera wrote:
> >>>> On 2020-Jul-01, Fujii Masao wrote:
> >>>>
> >>>>> On 2020/07/01 12:26, Alvaro Herrera wrote:
> >>>>>> On 2020-Jun-30, Fujii Masao wrote:
> >>>>>>
> >>>>>>> When I talked about max_slot_wal_keep_size as new feature in v13
> >>>>>>> at the conference, I received the question like "Why are the units of
> >>>>>>> setting values in max_slot_wal_keep_size and wal_keep_segments
> >>>>>>> different?"
> >>>>>>> from audience. That difference looks confusing for users and
> >>>>>>> IMO it's better to use the same unit for them. Thought?
> >>>>>>
> >>>>>> Do we still need wal_keep_segments for anything?
> >>>>>
> >>>>> Yeah, personally I like wal_keep_segments because its setting is very
> >>>>> simple and no extra operations on replication slots are necessary.
> >>>>
> >>>> Okay.  In that case I +1 the idea of renaming to wal_keep_size.
> >>> +1 for renaming to wal_keep_size.
> >>
> >> I attached the patch that renames wal_keep_segments to wal_keep_size.
> > It fails on 019_replslot_limit.pl for uncertain reason to me..
>
> I could not reproduce this...

Sorry for the ambiguity. The patch didn't applied on the file, and I
noticed that the reason is the wording change from master to
primary. So no problem in the latest patch.

> > @@ -11323,7 +11329,7 @@ do_pg_stop_backup(char *labelfile, bool
> > waitforarchive, TimeLineID *stoptli_p)
> > * If archiving is enabled, wait for all the required WAL files to be
> > * archived before returning. If archiving isn't enabled, the required
> > * WAL
> > * needs to be transported via streaming replication (hopefully with
> > - * wal_keep_segments set high enough), or some more exotic mechanism like
> > + * wal_keep_size set high enough), or some more exotic mechanism like
> > * polling and copying files from pg_wal with script. We have no
> > * knowledge
> > Isn't this time a good chance to mention replication slots?
>
> +1 to do that. But I found there are other places where replication
> slots
> need to be mentioned. So I think it's better to do this as separate
> patch.

Agreed.

> > - "ALTER SYSTEM SET wal_keep_segments to 8; SELECT pg_reload_conf();");
> > + "ALTER SYSTEM SET wal_keep_size to '128MB'; SELECT
> > pg_reload_conf();");
> > wal_segment_size to 1MB here so, that conversion is not correct.
> > (However, that test works as long as it is more than
> > max_slot_wal_keep_size so it's practically no problem.)
>
> So I changed 128MB to 8MB. Is this OK?
> I attached the updated version of the patch upthread.

That change looks find by me.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center