From 588ce747026bfdd0da5d6c0a95c73082cb9316d7 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Wed, 28 Nov 2018 10:15:55 -0500
Subject: [PATCH 3/8] Initial cut at PartitionDirectory.

---
 src/backend/partitioning/partdesc.c | 64 ++++++++++++++++++++++++++++-
 src/include/partitioning/partdefs.h |  2 +
 src/include/partitioning/partdesc.h |  3 ++
 3 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/src/backend/partitioning/partdesc.c b/src/backend/partitioning/partdesc.c
index 66b1e38527..a207ff35ee 100644
--- a/src/backend/partitioning/partdesc.c
+++ b/src/backend/partitioning/partdesc.c
@@ -21,12 +21,25 @@
 #include "storage/sinval.h"
 #include "utils/builtins.h"
 #include "utils/inval.h"
+#include "utils/hsearch.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 #include "utils/partcache.h"
 #include "utils/syscache.h"
 
+typedef struct PartitionDirectoryData
+{
+	MemoryContext pdir_mcxt;
+	HTAB	   *pdir_hash;
+} PartitionDirectoryData;
+
+typedef struct PartitionDirectoryEntry
+{
+	Oid			reloid;
+	PartitionDesc pd;
+} PartitionDirectoryEntry;
+
 /*
  * RelationBuildPartitionDesc
  *		Form rel's partition descriptor
@@ -208,13 +221,62 @@ RelationBuildPartitionDesc(Relation rel)
 		partdesc->oids[index] = oids[i];
 		/* Record if the partition is a leaf partition */
 		partdesc->is_leaf[index] =
-				(get_rel_relkind(oids[i]) != RELKIND_PARTITIONED_TABLE);
+			(get_rel_relkind(oids[i]) != RELKIND_PARTITIONED_TABLE);
 	}
 	MemoryContextSwitchTo(oldcxt);
 
 	rel->rd_partdesc = partdesc;
 }
 
+/*
+ * CreatePartitionDirectory
+ *		Create a new partition directory object.
+ */
+PartitionDirectory
+CreatePartitionDirectory(MemoryContext mcxt)
+{
+	MemoryContext oldcontext = MemoryContextSwitchTo(mcxt);
+	PartitionDirectory pdir;
+	HASHCTL		ctl;
+
+	MemSet(&ctl, 0, sizeof(HASHCTL));
+	ctl.keysize = sizeof(Oid);
+	ctl.entrysize = sizeof(PartitionDirectoryEntry);
+	ctl.hcxt = mcxt;
+
+	pdir = palloc(sizeof(PartitionDirectoryData));
+	pdir->pdir_mcxt = mcxt;
+	pdir->pdir_hash = hash_create("partition directory", 256, &ctl,
+								  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	MemoryContextSwitchTo(oldcontext);
+	return pdir;
+}
+
+/*
+ * PartitionDirectoryLookup
+ *		Look up the partition descriptor for a relation in the directory.
+ *
+ * The purpose of this function is to ensure that we get the same
+ * PartitionDesc for each relation every time we look it up.  In the
+ * face of current DDL, different PartitionDescs may be constructed with
+ * different views of the catalog state, but any single particular OID
+ * will always get the same PartitionDesc for as long as the same
+ * PartitionDirectory is used.
+ */
+PartitionDesc
+PartitionDirectoryLookup(PartitionDirectory pdir, Relation rel)
+{
+	PartitionDirectoryEntry *pde;
+	Oid			relid = RelationGetRelid(rel);
+	bool		found;
+
+	pde = hash_search(pdir->pdir_hash, &relid, HASH_ENTER, &found);
+	if (!found)
+		pde->pd = RelationGetPartitionDesc(rel);
+	return pde->pd;
+}
+
 /*
  * equalPartitionDescs
  *		Compare two partition descriptors for logical equality
diff --git a/src/include/partitioning/partdefs.h b/src/include/partitioning/partdefs.h
index 6e9c128b2c..aec3b3fe63 100644
--- a/src/include/partitioning/partdefs.h
+++ b/src/include/partitioning/partdefs.h
@@ -21,4 +21,6 @@ typedef struct PartitionBoundSpec PartitionBoundSpec;
 
 typedef struct PartitionDescData *PartitionDesc;
 
+typedef struct PartitionDirectoryData *PartitionDirectory;
+
 #endif							/* PARTDEFS_H */
diff --git a/src/include/partitioning/partdesc.h b/src/include/partitioning/partdesc.h
index f72b70dded..6e384541da 100644
--- a/src/include/partitioning/partdesc.h
+++ b/src/include/partitioning/partdesc.h
@@ -31,6 +31,9 @@ typedef struct PartitionDescData
 
 extern void RelationBuildPartitionDesc(Relation rel);
 
+extern PartitionDirectory CreatePartitionDirectory(MemoryContext mcxt);
+extern PartitionDesc PartitionDirectoryLookup(PartitionDirectory, Relation);
+
 extern Oid	get_default_oid_from_partdesc(PartitionDesc partdesc);
 
 extern bool equalPartitionDescs(PartitionKey key, PartitionDesc partdesc1,
-- 
2.17.2 (Apple Git-113)