Horton

Re: [HACKERS] WAL logging problem in 9.4.3?

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: noah@leadboat.com
Cc: robertmhaas@gmail.com, pgsql-hackers@postgresql.org, 9erthalion6@gmail.com, andrew.dunstan@2ndquadrant.com, hlinnaka@iki.fi, michael@paquier.xyz
Date: 2020-01-27T04:44:13Z
Lists: pgsql-hackers 
Thanks!

At Sun, 26 Jan 2020 20:22:01 -0800, Noah Misch <noah@leadboat.com> wrote in 
> Diffing the two latest versions of one patch:
> > --- v32-0002-Fix-the-defect-1.patch	2020-01-18 14:32:47.499129940 -0800
> > +++ v33-0002-Fix-the-defect-1.patch	2020-01-26 16:23:52.846391035 -0800
> > +@@ -2978,8 +3054,8 @@ AssertPendingSyncs_RelationCache(void)
> > + 			LOCKTAG_RELATION)
> > + 			continue;
> > + 		relid = ObjectIdGetDatum(locallock->tag.lock.locktag_field2);
> > +-		r = RelationIdGetRelation(relid);
> > +-		if (r == NULL)
> > ++		r = RelationIdGetRelationCache(relid);
> 
> The purpose of this loop is to create relcache entries for rels locked in the
> current transaction.  (The "r == NULL" case happens for rels no longer visible
> in catalogs.  It is harmless.)  Since RelationIdGetRelationCache() never
> creates a relcache entry, calling it defeats that purpose.
> RelationIdGetRelation() is the right function to call.

I thought that the all required entry exist in the cache but actually
it's safer that recreate dropped caches. Does the following works?

	r = RelationIdGetRelation(relid);
+       /* if not found, fetch a "dropped" entry if any  */
+	if (r == NULL)
+	    r = RelationIdGetRelationCache(relid);
	if (r == NULL)
	    continue;

> On Tue, Jan 21, 2020 at 06:45:57PM +0900, Kyotaro Horiguchi wrote:
> > Three other fixes not mentined above are made. One is the useless
> > rd_firstRelfilenodeSubid in the condition to dicide whether to
> > preserve or not a relcache entry
> 
> It was not useless.  Test case:
> 
>   create table t (c int);
>   begin;
>   alter table t alter c type bigint;  -- sets rd_firstRelfilenodeSubid
>   savepoint q; drop table t; rollback to q;  -- forgets rd_firstRelfilenodeSubid
>   commit;  -- assertion failure, after s/RelationIdGetRelationCache/RelationIdGetRelation/ discussed above

Mmm? I thought somehow that that relcache entry never be dropped and I
believe I considered that case, of course.  But yes, you're right.

I'll post upated version.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

Commits

  1. Add perl2host call missing from a new test file.

  2. Skip WAL for new relfilenodes, under wal_level=minimal.

  3. Revert "Skip WAL for new relfilenodes, under wal_level=minimal."

  4. Back-patch log_newpage_range().

  5. During heap rebuild, lock any TOAST index until end of transaction.

  6. In log_newpage_range(), heed forkNum and page_std arguments.

  7. Back-patch src/test/recovery and PostgresNode from 9.6 to 9.5.

  8. Reduce pg_ctl's reaction time when waiting for postmaster start/stop.

  9. Accelerate end-of-transaction dropping of relations

  10. Redesign the planner's handling of index-descent cost estimation.

  11. Make TRUNCATE do truncate-in-place when processing a relation that was created