From 1bf53093225794d01003c62d6fd0a4d2a8d06453 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Tue, 18 Dec 2018 18:55:37 -0500
Subject: [PATCH] Partition directory.

---
 src/backend/partitioning/Makefile   |  2 +-
 src/backend/partitioning/partdir.c  | 76 +++++++++++++++++++++++++++++
 src/include/partitioning/partdefs.h |  2 +
 src/include/partitioning/partdir.h  | 21 ++++++++
 4 files changed, 100 insertions(+), 1 deletion(-)
 create mode 100644 src/backend/partitioning/partdir.c
 create mode 100644 src/include/partitioning/partdir.h

diff --git a/src/backend/partitioning/Makefile b/src/backend/partitioning/Makefile
index 278fac3afa..a096b0a0bb 100644
--- a/src/backend/partitioning/Makefile
+++ b/src/backend/partitioning/Makefile
@@ -12,6 +12,6 @@ subdir = src/backend/partitioning
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = partprune.o partbounds.o
+OBJS = partprune.o partbounds.o partdir.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/partitioning/partdir.c b/src/backend/partitioning/partdir.c
new file mode 100644
index 0000000000..463d192f13
--- /dev/null
+++ b/src/backend/partitioning/partdir.c
@@ -0,0 +1,76 @@
+/*-------------------------------------------------------------------------
+ *
+ * partdir.c
+ *		Support for partition directories
+ *
+ * Partition directories provide a mechanism for looking up the
+ * PartitionDesc for a relation in such a way that the answer will be
+ * the same every time the directory is interrogated, even in the face
+ * of concurrent DDL.
+ *
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		  src/backend/partitioning/partdir.c
+ *
+ *-------------------------------------------------------------------------
+*/
+#include "postgres.h"
+
+#include "catalog/pg_class.h"
+#include "partitioning/partdir.h"
+#include "utils/hsearch.h"
+#include "utils/rel.h"
+
+typedef struct PartitionDirectoryData
+{
+	MemoryContext pdir_mcxt;
+	HTAB *pdir_htab;
+} PartitionDirectoryData;
+
+typedef struct PartitionDirectoryEntry
+{
+	Oid	relid;
+	PartitionDesc pd;
+} PartitionDirectoryEntry;
+
+PartitionDirectory
+CreatePartitionDirectory(MemoryContext mcxt)
+{
+	HASHCTL hctl;
+	MemoryContext oldcontext;
+	PartitionDirectory pdir;
+
+	hctl.keysize = sizeof(Oid);
+	hctl.entrysize = sizeof(PartitionDirectoryEntry);
+	hctl.hcxt = mcxt;
+
+	oldcontext = MemoryContextSwitchTo(mcxt);
+
+	pdir = palloc(sizeof(PartitionDirectoryData));
+	pdir->pdir_mcxt = mcxt;
+	pdir->pdir_htab = hash_create("PartitionDirectory", 256, &hctl,
+								  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	MemoryContextSwitchTo(oldcontext);
+	return pdir;
+}
+
+PartitionDesc
+PartitionDirectoryLookup(PartitionDirectory pdir, Relation rel)
+{
+	PartitionDirectoryEntry *pde;
+	Oid relid;
+	bool found;
+
+	Assert(rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
+	relid = RelationGetRelid(rel);
+	pde = hash_search(pdir->pdir_htab, &relid, HASH_ENTER, &found);
+	if (!found)
+	{
+		pde->pd = RelationGetPartitionDesc(rel);
+		Assert(pde->pd != NULL);
+	}
+	return pde->pd;
+}
diff --git a/src/include/partitioning/partdefs.h b/src/include/partitioning/partdefs.h
index 1fe1b4868e..9d94740d1d 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/partdir.h b/src/include/partitioning/partdir.h
new file mode 100644
index 0000000000..0472575bc1
--- /dev/null
+++ b/src/include/partitioning/partdir.h
@@ -0,0 +1,21 @@
+/*-------------------------------------------------------------------------
+ *
+ * partdir.h
+ *		A partition directory provides stable PartitionDesc lookups
+ *
+ * Copyright (c) 2007-2018, PostgreSQL Global Development Group
+ *
+ * src/include/partitioning/partdir.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PARTDIR_H
+#define PARTDIR_H
+
+#include "partitioning/partdefs.h"
+#include "utils/relcache.h"
+
+extern PartitionDirectory CreatePartitionDirectory(MemoryContext mcxt);
+extern PartitionDesc PartitionDirectoryLookup(PartitionDirectory, Relation);
+
+#endif							/* PARTDIR_H */
-- 
2.39.5