Allow a partdesc-omitting-partitions to be cached

Makes partition descriptor acquisition faster during the transient
period in which a partition is in the process of being detached.

This also adds the restriction that only one partition can be in
pending-detach state for a partitioned table.

While at it, return find_inheritance_children() API to what it was
before 71f4c8c6f74b, and create a separate
find_inheritance_children_extended() that returns detailed info about
detached partitions.

(This incidentally fixes a bug in 8aba9322511 whereby a memory context
holding a transient partdesc is reparented to a NULL PortalContext,
leading to permanent leak of that memory.  The fix is to no longer rely
on reparenting contexts to PortalContext.   Reported by Amit Langote.)

Per gripe from Amit Langote
Discussion: https://postgr.es/m/CA+HiwqFgpP1LxJZOBYGt9rpvTjXXkg5qG2+Xch2Z1Q7KrqZR1A@mail.gmail.com

1 files changed, 28 insertions, 5 deletions

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 466c28d5287..31c8e07f2a7 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -1157,7 +1157,10 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 	relation->rd_partkey = NULL;
 	relation->rd_partkeycxt = NULL;
 	relation->rd_partdesc = NULL;
+	relation->rd_partdesc_nodetached = NULL;
+	relation->rd_partdesc_nodetached_xmin = InvalidTransactionId;
 	relation->rd_pdcxt = NULL;
+	relation->rd_pddcxt = NULL;
 	relation->rd_partcheck = NIL;
 	relation->rd_partcheckvalid = false;
 	relation->rd_partcheckcxt = NULL;
@@ -2103,10 +2106,16 @@ RelationClose(Relation relation)
 	 * stale partition descriptors it has.  This is unlikely, so check to see
 	 * if there are child contexts before expending a call to mcxt.c.
 	 */
-	if (RelationHasReferenceCountZero(relation) &&
-		relation->rd_pdcxt != NULL &&
-		relation->rd_pdcxt->firstchild != NULL)
-		MemoryContextDeleteChildren(relation->rd_pdcxt);
+	if (RelationHasReferenceCountZero(relation))
+	{
+		if (relation->rd_pdcxt != NULL &&
+			relation->rd_pdcxt->firstchild != NULL)
+			MemoryContextDeleteChildren(relation->rd_pdcxt);
+
+		if (relation->rd_pddcxt != NULL &&
+			relation->rd_pddcxt->firstchild != NULL)
+			MemoryContextDeleteChildren(relation->rd_pddcxt);
+	}
 
 #ifdef RELCACHE_FORCE_RELEASE
 	if (RelationHasReferenceCountZero(relation) &&
@@ -2390,6 +2399,8 @@ RelationDestroyRelation(Relation relation, bool remember_tupdesc)
 		MemoryContextDelete(relation->rd_partkeycxt);
 	if (relation->rd_pdcxt)
 		MemoryContextDelete(relation->rd_pdcxt);
+	if (relation->rd_pddcxt)
+		MemoryContextDelete(relation->rd_pddcxt);
 	if (relation->rd_partcheckcxt)
 		MemoryContextDelete(relation->rd_partcheckcxt);
 	pfree(relation);
@@ -2644,7 +2655,7 @@ RelationClearRelation(Relation relation, bool rebuild)
 			SWAPFIELD(PartitionKey, rd_partkey);
 			SWAPFIELD(MemoryContext, rd_partkeycxt);
 		}
-		if (newrel->rd_pdcxt != NULL)
+		if (newrel->rd_pdcxt != NULL || newrel->rd_pddcxt != NULL)
 		{
 			/*
 			 * We are rebuilding a partitioned relation with a non-zero
@@ -2672,13 +2683,22 @@ RelationClearRelation(Relation relation, bool rebuild)
 			 * newrel.
 			 */
 			relation->rd_partdesc = NULL;	/* ensure rd_partdesc is invalid */
+			relation->rd_partdesc_nodetached = NULL;
+			relation->rd_partdesc_nodetached_xmin = InvalidTransactionId;
 			if (relation->rd_pdcxt != NULL) /* probably never happens */
 				MemoryContextSetParent(newrel->rd_pdcxt, relation->rd_pdcxt);
 			else
 				relation->rd_pdcxt = newrel->rd_pdcxt;
+			if (relation->rd_pddcxt != NULL)
+				MemoryContextSetParent(newrel->rd_pddcxt, relation->rd_pddcxt);
+			else
+				relation->rd_pddcxt = newrel->rd_pddcxt;
 			/* drop newrel's pointers so we don't destroy it below */
 			newrel->rd_partdesc = NULL;
+			newrel->rd_partdesc_nodetached = NULL;
+			newrel->rd_partdesc_nodetached_xmin = InvalidTransactionId;
 			newrel->rd_pdcxt = NULL;
+			newrel->rd_pddcxt = NULL;
 		}
 
 #undef SWAPFIELD
@@ -6017,7 +6037,10 @@ load_relcache_init_file(bool shared)
 		rel->rd_partkey = NULL;
 		rel->rd_partkeycxt = NULL;
 		rel->rd_partdesc = NULL;
+		rel->rd_partdesc_nodetached = NULL;
+		rel->rd_partdesc_nodetached_xmin = InvalidTransactionId;
 		rel->rd_pdcxt = NULL;
+		rel->rd_pddcxt = NULL;
 		rel->rd_partcheck = NIL;
 		rel->rd_partcheckvalid = false;
 		rel->rd_partcheckcxt = NULL;