Re: [HACKERS] WAL logging problem in 9.4.3?

At Tue, 18 Feb 2020 23:44:52 -0800, Noah Misch <noah(at)leadboat(dot)com> wrote in
> I think attached v35nm is ready for commit to master. Would anyone like to
> talk me out of back-patching this? I would not enjoy back-patching it, but
> it's hard to justify lack of back-patch for a data-loss bug.
>
> Notable changes since v34:
>
> - Separate a few freestanding fixes into their own patches.

All of the three patches look fine.

> On Mon, Jan 27, 2020 at 07:28:31PM +0900, Kyotaro Horiguchi wrote:
> > --- a/src/backend/catalog/storage.c
> > +++ b/src/backend/catalog/storage.c
> > @@ -388,13 +388,7 @@ RelationPreTruncate(Relation rel)
> > /* Record largest maybe-unsynced block of files under tracking */
> > pending = hash_search(pendingSyncHash, &(rel->rd_smgr->smgr_rnode.node),
> > HASH_FIND, NULL);
> > - if (pending)
> > - {
> > - BlockNumber nblocks = smgrnblocks(rel->rd_smgr, MAIN_FORKNUM);
> > -
> > - if (pending->max_truncated < nblocks)
> > - pending->max_truncated = nblocks;
> > - }
> > + pending->is_truncated = true;
>
> - Fix this crashing when "pending" is NULL, as it is in this test case:
>
> begin;
> create temp table t ();
> create table t2 (); -- cause pendingSyncHash to exist
> truncate t;
> rollback;

That's terrible... Thanks for fixint it.

> - Fix the "deleted while still in use" problem that Thomas Munro reported, by
> removing the heap_create() change. Restoring the saved rd_createSubid had
> made obsolete the heap_create() change. check-world now passes with
> wal_level=minimal and CLOBBER_CACHE_ALWAYS.

Ok, as in the previous mail.

> - Set rd_droppedSubid in RelationForgetRelation(), not
> RelationClearRelation(). RelationForgetRelation() knows it is processing a
> drop, but RelationClearRelation() could only infer that from circumstantial
> evidence. This seems more future-proof to me.

Agreed. Different from RelationClearRelatoin, RelationForgetRelation
is called only for "drop"ing the relation.

> - When reusing an index build, instead of storing the dropped relid in the
> IndexStmt and opening the dropped relcache entry in ATExecAddIndex(), store
> the subid fields in the IndexStmt. This is less code, and I felt
> RelationIdGetRelationCache() invited misuse.

Hmm. I'm not sure that index_create having the new subid parameters is
good. And the last if(OidIsValid) clause handles storage persistence
so I did that there. But I don't strongly against it.

Please give a bit more time to look it.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center