Re: contrib/pg_visibility fails regression under CLOBBER_CACHE_ALWAYS

On Mon, Jun 7, 2021 at 10:01 PM Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
>
>
>
> On 6/7/21 2:11 PM, Masahiko Sawada wrote:
> > On Mon, Jun 7, 2021 at 4:30 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >>
> >> On Mon, Jun 7, 2021 at 11:15 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >>>
> >>> husky just reported $SUBJECT:
> >>>
> >>> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=husky&dt=2021-06-05%2013%3A42%3A17
> >>>
> >>> and I find I can reproduce that locally:
> >>>
> >>> diff -U3 /home/postgres/pgsql/contrib/pg_visibility/expected/pg_visibility.out /home/postgres/pgsql/contrib/pg_visibility/results/pg_visibility.out
> >>> --- /home/postgres/pgsql/contrib/pg_visibility/expected/pg_visibility.out 2021-01-20 11:12:24.854346717 -0500
> >>> +++ /home/postgres/pgsql/contrib/pg_visibility/results/pg_visibility.out 2021-06-06 22:12:07.948890104 -0400
> >>> @@ -215,7 +215,8 @@
> >>> 0 | f | f
> >>> 1 | f | f
> >>> 2 | t | t
> >>> -(3 rows)
> >>> + 3 | t | t
> >>> +(4 rows)
> >>>
> >>> select * from pg_check_frozen('copyfreeze');
> >>> t_ctid
> >>> @@ -235,7 +236,8 @@
> >>> 0 | t | t
> >>> 1 | f | f
> >>> 2 | t | t
> >>> -(3 rows)
> >>> + 3 | t | t
> >>> +(4 rows)
> >>>
> >>> select * from pg_check_frozen('copyfreeze');
> >>> t_ctid
> >>>
> >>>
> >>> The test cases that are failing date back to January (7db0cd2145f),
> >>> so I think this is some side-effect of a recent commit, but I have
> >>> no idea which one.
> >>
> >> It seems like the recent revert (8e03eb92e9a) is relevant.
> >>
> >> After committing 7db0cd2145f we had the same regression test failure
> >> in January[1]. Then we fixed that issue by 39b66a91b. But since we
> >> recently reverted most of 39b66a91b, the same issue happened again.
> >>
> >
> > So the cause of this failure seems the same as before. The failed test is,
> >
> > begin;
> > truncate copyfreeze;
> > copy copyfreeze from stdin freeze;
> > 1 '1'
> > 2 '2'
> > 3 '3'
> > 4 '4'
> > 5 '5'
> > \.
> > copy copyfreeze from stdin;
> > 6 '6'
> > \.
> > copy copyfreeze from stdin freeze;
> > 7 '7'
> > 8 '8'
> > 9 '9'
> > 10 '10'
> > 11 '11'
> > 12 '12'
> > \.
> > commit;
> >
> > If the target block cache is invalidated before the third COPY, we
> > will start to insert the frozen tuple into a new page, resulting in
> > adding two blocks in total during the third COPY. I think we still
> > need the following part of the reverted code so that we don't leave
> > the page partially empty after relcache invalidation:
> >
> > --- a/src/backend/access/heap/hio.c
> > +++ b/src/backend/access/heap/hio.c
> > @@ -407,19 +407,19 @@ RelationGetBufferForTuple(Relation relation, Size len,
> > * target.
> > */
> > targetBlock = GetPageWithFreeSpace(relation, targetFreeSpace);
> > - }
> >
> > - /*
> > - * If the FSM knows nothing of the rel, try the last page before we give
> > - * up and extend. This avoids one-tuple-per-page syndrome during
> > - * bootstrapping or in a recently-started system.
> > - */
> > - if (targetBlock == InvalidBlockNumber)
> > - {
> > - BlockNumber nblocks = RelationGetNumberOfBlocks(relation);
> > + /*
> > + * If the FSM knows nothing of the rel, try the last page before we
> > + * give up and extend. This avoids one-tuple-per-page syndrome during
> > + * bootstrapping or in a recently-started system.
> > + */
> > + if (targetBlock == InvalidBlockNumber)
> > + {
> > + BlockNumber nblocks = RelationGetNumberOfBlocks(relation);
> >
> > - if (nblocks > 0)
> > - targetBlock = nblocks - 1;
> > + if (nblocks > 0)
> > + targetBlock = nblocks - 1;
> > + }
> > }
> >
> > Attached the patch that brings back the above change.
> >
>
> Thanks for the analysis! I think you're right - this bit should have
> been kept. Partial reverts are tricky :-(
>
> I'll get this fixed / pushed later today, after a bit more testing. I'd
> swear I ran tests with CCA, but it's possible I skipped contrib.

I had missed this mail. Thank you for pushing the fix!

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/