Re: [Patch] Optimize dropping of relation buffers using dlist

On Wed, Dec 9, 2020 at 6:32 AM Kyotaro Horiguchi
<horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Tue, 8 Dec 2020 16:28:41 +0530, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote in
> > On Tue, Dec 8, 2020 at 12:13 PM tsunakawa(dot)takay(at)fujitsu(dot)com
> > <tsunakawa(dot)takay(at)fujitsu(dot)com> wrote:
> > >
> > > From: Jamison, Kirk/ジャミソン カーク <k(dot)jamison(at)fujitsu(dot)com>
> > > > Because one of the rel's cached value was false, it forced the
> > > > full-scan path for TRUNCATE.
> > > > Is there a possible workaround for this?
> > >
> > > Hmm, the other two relfilenodes are for the TOAST table and index of the target table. I think the INSERT didn't access those TOAST relfilenodes because the inserted data was stored in the main storage. But TRUNCATE always truncates all the three relfilenodes. So, the standby had not opened the relfilenode for the TOAST stuff or cached its size when replaying the TRUNCATE.
> > >
> > > I'm afraid this is more common than we can ignore and accept the slow traditional path, but I don't think of a good idea to use the cached flag.
> > >
> >
> > I also can't think of a way to use an optimized path for such cases
> > but I don't agree with your comment on if it is common enough that we
> > leave this optimization entirely for the truncate path.
>
> Mmm. At least btree doesn't need to call smgrnblocks except at
> expansion, so we cannot get to the optimized path in major cases of
> truncation involving btree (and/or maybe other indexes).
>

AFAICS, btree insert should call smgrnblocks via
btree_xlog_insert->XLogReadBufferForRedo->XLogReadBufferForRedoExtended->XLogReadBufferExtended->smgrnblocks.
Similarly delete should also call smgrnblocks. Can you be bit more
specific related to the btree case you have in mind?

--
With Regards,
Amit Kapila.