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Commit258cef1

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Fix possibile deadlock when dropping partitions.
heap_drop_with_catalog and RangeVarCallbackForDropRelation shouldlock the parent before locking the target relation.Amit LangoteDiscussion:http://postgr.es/m/29588799-a8ce-b0a2-3dae-f39ff6d35922@lab.ntt.co.jp
1 parentfeffa0e commit258cef1

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2 files changed

+47
-13
lines changed

2 files changed

+47
-13
lines changed

‎src/backend/catalog/heap.c

Lines changed: 17 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -1759,29 +1759,33 @@ void
17591759
heap_drop_with_catalog(Oidrelid)
17601760
{
17611761
Relationrel;
1762+
HeapTupletuple;
17621763
OidparentOid;
17631764
Relationparent=NULL;
17641765

17651766
/*
1766-
* Open and lock the relation.
1767+
* To drop a partition safely, we must grab exclusive lock on its parent,
1768+
* because another backend might be about to execute a query on the parent
1769+
* table. If it relies on previously cached partition descriptor, then
1770+
* it could attempt to access the just-dropped relation as its partition.
1771+
* We must therefore take a table lock strong enough to prevent all
1772+
* queries on the table from proceeding until we commit and send out a
1773+
* shared-cache-inval notice that will make them update their index lists.
17671774
*/
1768-
rel=relation_open(relid,AccessExclusiveLock);
1769-
1770-
/*
1771-
* If the relation is a partition, we must grab exclusive lock on its
1772-
* parent because we need to update its partition descriptor. We must take
1773-
* a table lock strong enough to prevent all queries on the parent from
1774-
* proceeding until we commit and send out a shared-cache-inval notice
1775-
* that will make them update their partition descriptor. Sometimes, doing
1776-
* this is cycles spent uselessly, especially if the parent will be
1777-
* dropped as part of the same command anyway.
1778-
*/
1779-
if (rel->rd_rel->relispartition)
1775+
tuple=SearchSysCache1(RELOID,ObjectIdGetDatum(relid));
1776+
if (((Form_pg_class)GETSTRUCT(tuple))->relispartition)
17801777
{
17811778
parentOid=get_partition_parent(relid);
17821779
parent=heap_open(parentOid,AccessExclusiveLock);
17831780
}
17841781

1782+
ReleaseSysCache(tuple);
1783+
1784+
/*
1785+
* Open and lock the relation.
1786+
*/
1787+
rel=relation_open(relid,AccessExclusiveLock);
1788+
17851789
/*
17861790
* There can no longer be anyone *else* touching the relation, but we
17871791
* might still have open queries or cursors, or pending trigger events, in

‎src/backend/commands/tablecmds.c

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -271,6 +271,7 @@ struct DropRelationCallbackState
271271
{
272272
charrelkind;
273273
OidheapOid;
274+
OidpartParentOid;
274275
boolconcurrent;
275276
};
276277

@@ -1049,6 +1050,7 @@ RemoveRelations(DropStmt *drop)
10491050
/* Look up the appropriate relation using namespace search. */
10501051
state.relkind=relkind;
10511052
state.heapOid=InvalidOid;
1053+
state.partParentOid=InvalidOid;
10521054
state.concurrent=drop->concurrent;
10531055
relOid=RangeVarGetRelidExtended(rel,lockmode, true,
10541056
false,
@@ -1078,6 +1080,8 @@ RemoveRelations(DropStmt *drop)
10781080
/*
10791081
* Before acquiring a table lock, check whether we have sufficient rights.
10801082
* In the case of DROP INDEX, also try to lock the table before the index.
1083+
* Also, if the table to be dropped is a partition, we try to lock the parent
1084+
* first.
10811085
*/
10821086
staticvoid
10831087
RangeVarCallbackForDropRelation(constRangeVar*rel,OidrelOid,OidoldRelOid,
@@ -1087,6 +1091,7 @@ RangeVarCallbackForDropRelation(const RangeVar *rel, Oid relOid, Oid oldRelOid,
10871091
structDropRelationCallbackState*state;
10881092
charrelkind;
10891093
charexpected_relkind;
1094+
boolis_partition;
10901095
Form_pg_classclassform;
10911096
LOCKMODEheap_lockmode;
10921097

@@ -1106,6 +1111,17 @@ RangeVarCallbackForDropRelation(const RangeVar *rel, Oid relOid, Oid oldRelOid,
11061111
state->heapOid=InvalidOid;
11071112
}
11081113

1114+
/*
1115+
* Similarly, if we previously locked some other partition's heap, and
1116+
* the name we're looking up no longer refers to that relation, release
1117+
* the now-useless lock.
1118+
*/
1119+
if (relOid!=oldRelOid&&OidIsValid(state->partParentOid))
1120+
{
1121+
UnlockRelationOid(state->partParentOid,AccessExclusiveLock);
1122+
state->partParentOid=InvalidOid;
1123+
}
1124+
11091125
/* Didn't find a relation, so no need for locking or permission checks. */
11101126
if (!OidIsValid(relOid))
11111127
return;
@@ -1114,6 +1130,7 @@ RangeVarCallbackForDropRelation(const RangeVar *rel, Oid relOid, Oid oldRelOid,
11141130
if (!HeapTupleIsValid(tuple))
11151131
return;/* concurrently dropped, so nothing to do */
11161132
classform= (Form_pg_class)GETSTRUCT(tuple);
1133+
is_partition=classform->relispartition;
11171134

11181135
/*
11191136
* Both RELKIND_RELATION and RELKIND_PARTITIONED_TABLE are OBJECT_TABLE,
@@ -1157,6 +1174,19 @@ RangeVarCallbackForDropRelation(const RangeVar *rel, Oid relOid, Oid oldRelOid,
11571174
if (OidIsValid(state->heapOid))
11581175
LockRelationOid(state->heapOid,heap_lockmode);
11591176
}
1177+
1178+
/*
1179+
* Similarly, if the relation is a partition, we must acquire lock on its
1180+
* parent before locking the partition. That's because queries lock the
1181+
* parent before its partitions, so we risk deadlock it we do it the other
1182+
* way around.
1183+
*/
1184+
if (is_partition&&relOid!=oldRelOid)
1185+
{
1186+
state->partParentOid=get_partition_parent(relOid);
1187+
if (OidIsValid(state->partParentOid))
1188+
LockRelationOid(state->partParentOid,AccessExclusiveLock);
1189+
}
11601190
}
11611191

11621192
/*

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