From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Wed, 13 Nov 2019 15:34:13 -0300
Subject: [PATCH 2/2] Invoke RelationBuildPartitionDesc lazily

---
 src/backend/partitioning/partdesc.c | 17 ++++++++++++++++-
 src/backend/utils/cache/relcache.c  | 22 +++++-----------------
 src/include/partitioning/partdesc.h |  2 +-
 src/include/utils/rel.h             |  6 ------
 4 files changed, 22 insertions(+), 25 deletions(-)

diff --git a/src/backend/partitioning/partdesc.c b/src/backend/partitioning/partdesc.c
index c551df6673..8171eb03ca 100644
--- a/src/backend/partitioning/partdesc.c
+++ b/src/backend/partitioning/partdesc.c
@@ -34,6 +34,7 @@
 #include "utils/rel.h"
 #include "utils/syscache.h"
 
+
 typedef struct PartitionDirectoryData
 {
 	MemoryContext pdir_mcxt;
@@ -47,6 +48,20 @@ typedef struct PartitionDirectoryEntry
 	PartitionDesc pd;
 } PartitionDirectoryEntry;
 
+
+static void RelationBuildPartitionDesc(Relation rel);
+
+PartitionDesc
+RelationGetPartitionDesc(Relation rel)
+{
+	Assert(rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
+
+	if (rel->rd_partdesc == NULL)
+		RelationBuildPartitionDesc(rel);
+
+	return rel->rd_partdesc;
+}
+
 /*
  * RelationBuildPartitionDesc
  *		Form rel's partition descriptor, and store in relcache entry
@@ -57,7 +72,7 @@ typedef struct PartitionDirectoryEntry
  * that's sufficient to prevent that can assume that rd_partdesc
  * won't change underneath it.
  */
-void
+static void
 RelationBuildPartitionDesc(Relation rel)
 {
 	PartitionDesc partdesc;
diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index ad1ff01b32..5ef61d187a 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -1165,20 +1165,17 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 	relation->rd_fkeylist = NIL;
 	relation->rd_fkeyvalid = false;
 
-	/* if a partitioned table, initialize key and partition descriptor info */
+	/* if a partitioned table, initialize key info */
 	if (relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
-	{
 		RelationBuildPartitionKey(relation);
-		RelationBuildPartitionDesc(relation);
-	}
 	else
 	{
 		relation->rd_partkey = NULL;
 		relation->rd_partkeycxt = NULL;
-		relation->rd_partdesc = NULL;
-		relation->rd_pdcxt = NULL;
 	}
-	/* ... but partcheck is not loaded till asked for */
+	/* ... but partcheck and partdesc are not loaded till asked for */
+	relation->rd_pdcxt = NULL;
+	relation->rd_partdesc = NULL;
 	relation->rd_partcheck = NIL;
 	relation->rd_partcheckvalid = false;
 	relation->rd_partcheckcxt = NULL;
@@ -3908,7 +3905,7 @@ RelationCacheInitializePhase3(void)
 		}
 
 		/*
-		 * Reload the partition key and descriptor for a partitioned table.
+		 * Reload the partition key for a partitioned table.
 		 */
 		if (relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE &&
 			relation->rd_partkey == NULL)
@@ -3919,15 +3916,6 @@ RelationCacheInitializePhase3(void)
 			restart = true;
 		}
 
-		if (relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE &&
-			relation->rd_partdesc == NULL)
-		{
-			RelationBuildPartitionDesc(relation);
-			Assert(relation->rd_partdesc != NULL);
-
-			restart = true;
-		}
-
 		if (relation->rd_tableam == NULL &&
 			(relation->rd_rel->relkind == RELKIND_RELATION ||
 			 relation->rd_rel->relkind == RELKIND_SEQUENCE ||
diff --git a/src/include/partitioning/partdesc.h b/src/include/partitioning/partdesc.h
index 38712c1550..d30c8feb48 100644
--- a/src/include/partitioning/partdesc.h
+++ b/src/include/partitioning/partdesc.h
@@ -29,7 +29,7 @@ typedef struct PartitionDescData
 	PartitionBoundInfo boundinfo;	/* collection of partition bounds */
 } PartitionDescData;
 
-extern void RelationBuildPartitionDesc(Relation rel);
+extern PartitionDesc RelationGetPartitionDesc(Relation rel);
 
 extern PartitionDirectory CreatePartitionDirectory(MemoryContext mcxt);
 extern PartitionDesc PartitionDirectoryLookup(PartitionDirectory, Relation);
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index 8b8b237f0d..4ec27a63e8 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -603,12 +603,6 @@ typedef struct ViewOptions
  */
 #define RelationGetPartitionKey(relation) ((relation)->rd_partkey)
 
-/*
- * RelationGetPartitionDesc
- *		Returns partition descriptor for a relation.
- */
-#define RelationGetPartitionDesc(relation) ((relation)->rd_partdesc)
-
 /* routines in utils/cache/relcache.c */
 extern void RelationIncrementReferenceCount(Relation rel);
 extern void RelationDecrementReferenceCount(Relation rel);
-- 
2.20.1


--OXfL5xGRrasGEqWY--