Date: Tue, 8 Sep 2020 21:05:43 -0700
From: Noah Misch <noah@leadboat.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: tgl@sss.pgh.pa.us, pryzby@telsasoft.com, pgsql-hackers@postgresql.org
Subject: Re: v13: CLUSTER segv with wal_level=minimal and parallel index
 creation
Message-ID: <20200909040543.GA15541@rfd.leadboat.com>
References: <20200907.174036.603784943439284546.horikyota.ntt@gmail.com>
 <20200907093255.GA3609623@rfd.leadboat.com>
 <20200908.091353.1505164218636547516.horikyota.ntt@gmail.com>
 <20200908.104332.1790214922230554649.horikyota.ntt@gmail.com>
 <20200908024709.GA3640955@rfd.leadboat.com>
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On Mon, Sep 07, 2020 at 07:47:09PM -0700, Noah Misch wrote:
> On Tue, Sep 08, 2020 at 10:43:32AM +0900, Kyotaro Horiguchi wrote:
> > At Tue, 08 Sep 2020 09:13:53 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> > > At Mon, 7 Sep 2020 02:32:55 -0700, Noah Misch <noah@leadboat.com> wrote in 
> > > > As a PoC, this looks promising.  Thanks.  Would you add a test case such that
> > > > the following demonstrates the bug in the absence of your PoC?
> > > > 
> > > >   printf '%s\n%s\n%s\n' 'log_statement = all' 'wal_level = minimal' 'max_wal_senders = 0' >/tmp/minimal.conf
> > > >   make check TEMP_CONFIG=/tmp/minimal.conf
> > > 
> > > Mmm. I was close to add some tests to 018_wal_optimize.pl but your
> > > suggestion seems better.  I added several ines to create_index.sql.

After looking closer, I've moved the test to reindex_catalog.sql; see that
file's header comment for the reasons.  One now needs this command:

  printf '%s\n%s\n%s\n' 'log_statement = all' 'wal_level = minimal' 'max_wal_senders = 0' >/tmp/minimal.conf
  make check-tests TESTS=reindex_catalog TEMP_CONFIG=/tmp/minimal.conf

> > > > Please have the test try both a nailed-and-mapped relation and a "nailed, but
> > > > not mapped" relation.  I am fairly confident that your PoC fixes the former
> > > > case, but the latter may need additional code.
> > > 
> > > Mmm. You're right. I choosed pg_amproc_fam_proc_index as
> > > nailed-but-not-mapped index.
> > 
> > I fixed a typo (s/staring/starting/).
> 
> At a glance, this looks reasonable.  If a closer look doesn't reveal problems,
> I'll push this.

RelationBuildDesc() calls RelationInitPhysicalAddr(), so RelationBuildDesc()
can stop calling RelFileNodeSkippingWAL().  The attached version makes it so,
and I plan to push it.

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Author:     Noah Misch <noah@leadboat.com>
Commit:     Noah Misch <noah@leadboat.com>

    Fix rd_firstRelfilenodeSubid for nailed relations, in parallel workers.
    
    Move applicable code out of RelationBuildDesc(), which nailed relations
    bypass.  Non-assert builds experienced no known problems.  Back-patch to
    v13, where commit c6b92041d38512a4176ed76ad06f713d2e6c01a8 introduced
    rd_firstRelfilenodeSubid.
    
    Kyotaro Horiguchi.  Reported by Justin Pryzby.
    
    Discussion: https://postgr.es/m/20200907023737.GA7158@telsasoft.com

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 96ecad0..9061af8 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -1243,14 +1243,6 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 	if (insertIt)
 		RelationCacheInsert(relation, true);
 
-	/*
-	 * For RelationNeedsWAL() to answer correctly on parallel workers, restore
-	 * rd_firstRelfilenodeSubid.  No subtransactions start or end while in
-	 * parallel mode, so the specific SubTransactionId does not matter.
-	 */
-	if (IsParallelWorker() && RelFileNodeSkippingWAL(relation->rd_node))
-		relation->rd_firstRelfilenodeSubid = TopSubTransactionId;
-
 	/* It's fully valid */
 	relation->rd_isvalid = true;
 
@@ -1273,6 +1265,8 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 static void
 RelationInitPhysicalAddr(Relation relation)
 {
+	Oid			oldnode = relation->rd_node.relNode;
+
 	/* these relations kinds never have storage */
 	if (!RELKIND_HAS_STORAGE(relation->rd_rel->relkind))
 		return;
@@ -1330,6 +1324,19 @@ RelationInitPhysicalAddr(Relation relation)
 			elog(ERROR, "could not find relation mapping for relation \"%s\", OID %u",
 				 RelationGetRelationName(relation), relation->rd_id);
 	}
+
+	/*
+	 * For RelationNeedsWAL() to answer correctly on parallel workers, restore
+	 * rd_firstRelfilenodeSubid.  No subtransactions start or end while in
+	 * parallel mode, so the specific SubTransactionId does not matter.
+	 */
+	if (IsParallelWorker() && oldnode != relation->rd_node.relNode)
+	{
+		if (RelFileNodeSkippingWAL(relation->rd_node))
+			relation->rd_firstRelfilenodeSubid = TopSubTransactionId;
+		else
+			relation->rd_firstRelfilenodeSubid = InvalidSubTransactionId;
+	}
 }
 
 /*
diff --git a/src/test/regress/expected/reindex_catalog.out b/src/test/regress/expected/reindex_catalog.out
index 4b5fba4..204f056 100644
--- a/src/test/regress/expected/reindex_catalog.out
+++ b/src/test/regress/expected/reindex_catalog.out
@@ -36,3 +36,13 @@ REINDEX INDEX pg_index_indexrelid_index; -- non-mapped, non-shared, critical
 REINDEX INDEX pg_index_indrelid_index; -- non-mapped, non-shared, non-critical
 REINDEX INDEX pg_database_oid_index; -- mapped, shared, critical
 REINDEX INDEX pg_shdescription_o_c_index; -- mapped, shared, non-critical
+-- Check the same REINDEX INDEX statements under parallelism.
+BEGIN;
+SET min_parallel_table_scan_size = 0;
+REINDEX INDEX pg_class_oid_index; -- mapped, non-shared, critical
+REINDEX INDEX pg_class_relname_nsp_index; -- mapped, non-shared, non-critical
+REINDEX INDEX pg_index_indexrelid_index; -- non-mapped, non-shared, critical
+REINDEX INDEX pg_index_indrelid_index; -- non-mapped, non-shared, non-critical
+REINDEX INDEX pg_database_oid_index; -- mapped, shared, critical
+REINDEX INDEX pg_shdescription_o_c_index; -- mapped, shared, non-critical
+ROLLBACK;
diff --git a/src/test/regress/sql/reindex_catalog.sql b/src/test/regress/sql/reindex_catalog.sql
index 87ecf52..8203641 100644
--- a/src/test/regress/sql/reindex_catalog.sql
+++ b/src/test/regress/sql/reindex_catalog.sql
@@ -39,3 +39,14 @@ REINDEX INDEX pg_index_indexrelid_index; -- non-mapped, non-shared, critical
 REINDEX INDEX pg_index_indrelid_index; -- non-mapped, non-shared, non-critical
 REINDEX INDEX pg_database_oid_index; -- mapped, shared, critical
 REINDEX INDEX pg_shdescription_o_c_index; -- mapped, shared, non-critical
+
+-- Check the same REINDEX INDEX statements under parallelism.
+BEGIN;
+SET min_parallel_table_scan_size = 0;
+REINDEX INDEX pg_class_oid_index; -- mapped, non-shared, critical
+REINDEX INDEX pg_class_relname_nsp_index; -- mapped, non-shared, non-critical
+REINDEX INDEX pg_index_indexrelid_index; -- non-mapped, non-shared, critical
+REINDEX INDEX pg_index_indrelid_index; -- non-mapped, non-shared, non-critical
+REINDEX INDEX pg_database_oid_index; -- mapped, shared, critical
+REINDEX INDEX pg_shdescription_o_c_index; -- mapped, shared, non-critical
+ROLLBACK;

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