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Commit5236dcd

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Fix creation of partition descriptor during concurrent detach+drop
If a partition undergoes DETACH CONCURRENTLY immediately followed byDROP, this could cause a problem for a concurrent transactionrecomputing the partition descriptor when running a prepared statement,because it tries to dereference a pointer to a tuple that's not found ina catalog scan.The existing retry logic added in commitdbca346 is sufficient tocope with the overall problem, provided we don't try to dereference anon-existant heap tuple.Arguably, the code in RelationBuildPartitionDesc() has been wrong allalong, since no check was added in commit898e5e3 against receivinga NULL tuple from the catalog scan; that bug has only becomeuser-visible with DETACH CONCURRENTLY which was added in branch 14.Therefore, even though there's no known mechanism to cause a crashbecause of this, backpatch the addition of such a check to all supportedbranches. In branches prior to 14, this would cause the code to failwith a "missing relpartbound for relation XYZ" error instead ofcrashing; that's okay, because there are no reports of such behavioranyway.Author: Kuntal Ghosh <kuntalghosh.2007@gmail.com>Reviewed-by: Junwang Zhao <zhjwpku@gmail.com>Reviewed-by: Tender Wang <tndrwang@gmail.com>Discussion:https://postgr.es/m/18559-b48286d2eacd9a4e@postgresql.org
1 parent016f443 commit5236dcd

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‎src/backend/partitioning/partdesc.c

Lines changed: 10 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -164,8 +164,6 @@ RelationBuildPartitionDesc(Relation rel)
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Relationpg_class;
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SysScanDescscan;
166166
ScanKeyDatakey[1];
167-
Datumdatum;
168-
boolisnull;
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170168
pg_class=table_open(RelationRelationId,AccessShareLock);
171169
ScanKeyInit(&key[0],
@@ -175,10 +173,16 @@ RelationBuildPartitionDesc(Relation rel)
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scan=systable_beginscan(pg_class,ClassOidIndexId, true,
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NULL,1,key);
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tuple=systable_getnext(scan);
178-
datum=heap_getattr(tuple,Anum_pg_class_relpartbound,
179-
RelationGetDescr(pg_class),&isnull);
180-
if (!isnull)
181-
boundspec=stringToNode(TextDatumGetCString(datum));
176+
if (HeapTupleIsValid(tuple))
177+
{
178+
Datumdatum;
179+
boolisnull;
180+
181+
datum=heap_getattr(tuple,Anum_pg_class_relpartbound,
182+
RelationGetDescr(pg_class),&isnull);
183+
if (!isnull)
184+
boundspec=stringToNode(TextDatumGetCString(datum));
185+
}
182186
systable_endscan(scan);
183187
table_close(pg_class,AccessShareLock);
184188
}

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