Support ALTER TABLESPACE name SET/RESET ( tablespace_options ).

This patch only supports seq_page_cost and random_page_cost as parameters,
but it provides the infrastructure to scalably support many more.
In particular, we may want to add support for effective_io_concurrency,
but I'm leaving that as future work for now.

Thanks to Tom Lane for design help and Alvaro Herrera for the review.

src/backend/utils/cache/Makefile

@@ -4,7 +4,7 @@
 #    Makefile for utils/cache
 #
 # IDENTIFICATION
-#    $PostgreSQL: pgsql/src/backend/utils/cache/Makefile,v 1.23 2008/02/19 10:30:08 petere Exp $
+#    $PostgreSQL: pgsql/src/backend/utils/cache/Makefile,v 1.24 2010/01/05 21:53:59 rhaas Exp $
 #
 #-------------------------------------------------------------------------
 
@@ -13,6 +13,6 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = catcache.o inval.o plancache.o relcache.o \
-	syscache.o lsyscache.o typcache.o ts_cache.o
+	spccache.o syscache.o lsyscache.o typcache.o ts_cache.o
 
 include $(top_srcdir)/src/backend/common.mk

src/backend/utils/cache/spccache.c

@@ -0,0 +1,183 @@
+/*-------------------------------------------------------------------------
+ *
+ * spccache.c
+ *	  Tablespace cache management.
+ *
+ * We cache the parsed version of spcoptions for each tablespace to avoid
+ * needing to reparse on every lookup.  Right now, there doesn't appear to
+ * be a measurable performance gain from doing this, but that might change
+ * in the future as we add more options.
+ *
+ * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/backend/utils/cache/spccache.c,v 1.1 2010/01/05 21:53:59 rhaas Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+#include "access/reloptions.h"
+#include "catalog/pg_tablespace.h"
+#include "commands/tablespace.h"
+#include "miscadmin.h"
+#include "optimizer/cost.h"
+#include "utils/catcache.h"
+#include "utils/hsearch.h"
+#include "utils/inval.h"
+#include "utils/spccache.h"
+#include "utils/syscache.h"
+
+static HTAB *TableSpaceCacheHash = NULL;
+
+typedef struct {
+	Oid			oid;
+	TableSpaceOpts *opts;
+} TableSpace;
+
+/*
+ * InvalidateTableSpaceCacheCallback
+ *		Flush all cache entries when pg_tablespace is updated.
+ *
+ * When pg_tablespace is updated, we must flush the cache entry at least
+ * for that tablespace.  Currently, we just flush them all.  This is quick
+ * and easy and doesn't cost much, since there shouldn't be terribly many
+ * tablespaces, nor do we expect them to be frequently modified.
+ */
+static void
+InvalidateTableSpaceCacheCallback(Datum arg, int cacheid, ItemPointer tuplePtr)
+{
+	HASH_SEQ_STATUS status;
+	TableSpace *spc;
+
+	hash_seq_init(&status, TableSpaceCacheHash);
+	while ((spc = (TableSpace *) hash_seq_search(&status)) != NULL)
+	{
+		if (hash_search(TableSpaceCacheHash, (void *) &spc->oid, HASH_REMOVE,
+						NULL) == NULL)
+			elog(ERROR, "hash table corrupted");
+		if (spc->opts)
+			pfree(spc->opts);
+	}
+}
+
+/*
+ * InitializeTableSpaceCache
+ *		Initiate the tablespace cache.
+ */
+static void
+InitializeTableSpaceCache(void)
+{
+	HASHCTL ctl;
+
+	/* Initialize the hash table. */
+	MemSet(&ctl, 0, sizeof(ctl));
+	ctl.keysize = sizeof(Oid);
+	ctl.entrysize = sizeof(TableSpace);
+	ctl.hash = tag_hash;
+	TableSpaceCacheHash =
+		hash_create("TableSpace cache", 16, &ctl,
+				    HASH_ELEM | HASH_FUNCTION);
+
+	/* Make sure we've initialized CacheMemoryContext. */
+	if (!CacheMemoryContext)
+		CreateCacheMemoryContext();
+
+	/* Watch for invalidation events. */
+	CacheRegisterSyscacheCallback(TABLESPACEOID,
+								  InvalidateTableSpaceCacheCallback,
+								  (Datum) 0);
+}
+
+/*
+ * get_tablespace
+ *		Fetch TableSpace structure for a specified table OID.
+ *
+ * Pointers returned by this function should not be stored, since a cache
+ * flush will invalidate them.
+ */
+static TableSpace *
+get_tablespace(Oid spcid)
+{
+	HeapTuple	tp;
+	TableSpace *spc;
+	bool		found;
+
+	/*
+	 * Since spcid is always from a pg_class tuple, InvalidOid implies the
+	 * default.
+	 */
+	if (spcid == InvalidOid)
+		spcid = MyDatabaseTableSpace;
+
+	/* Find existing cache entry, or create a new one. */
+	if (!TableSpaceCacheHash)
+		InitializeTableSpaceCache();
+	spc = (TableSpace *) hash_search(TableSpaceCacheHash, (void *) &spcid,
+									 HASH_ENTER, &found);
+	if (found)
+		return spc;
+
+	/*
+	 * Not found in TableSpace cache.  Check catcache.  If we don't find a
+	 * valid HeapTuple, it must mean someone has managed to request tablespace
+	 * details for a non-existent tablespace.  We'll just treat that case as if
+	 * no options were specified.
+	 */
+	tp = SearchSysCache(TABLESPACEOID, ObjectIdGetDatum(spcid), 0, 0, 0);
+	if (!HeapTupleIsValid(tp))
+		spc->opts = NULL;
+	else
+	{
+		Datum	datum;
+		bool	isNull;
+		MemoryContext octx;
+
+		datum = SysCacheGetAttr(TABLESPACEOID,
+								tp,
+								Anum_pg_tablespace_spcoptions,
+								&isNull);
+		if (isNull)
+			spc->opts = NULL;
+		else
+		{
+			octx = MemoryContextSwitchTo(CacheMemoryContext);
+			spc->opts = (TableSpaceOpts *) tablespace_reloptions(datum, false);
+			MemoryContextSwitchTo(octx);
+		}
+		ReleaseSysCache(tp);
+	}
+
+	/* Update new TableSpace cache entry with results of option parsing. */
+	return spc;
+}
+
+/*
+ * get_tablespace_page_costs
+ *		Return random and sequential page costs for a given tablespace.
+ */
+void
+get_tablespace_page_costs(Oid spcid, double *spc_random_page_cost,
+							   double *spc_seq_page_cost)
+{
+	TableSpace *spc = get_tablespace(spcid);
+
+	Assert(spc != NULL);
+
+	if (spc_random_page_cost)
+	{
+		if (!spc->opts || spc->opts->random_page_cost < 0)
+			*spc_random_page_cost = random_page_cost;
+		else
+			*spc_random_page_cost = spc->opts->random_page_cost;
+	}
+
+	if (spc_seq_page_cost)
+	{
+		if (!spc->opts || spc->opts->seq_page_cost < 0)
+			*spc_seq_page_cost = seq_page_cost;
+		else
+			*spc_seq_page_cost = spc->opts->seq_page_cost;
+	}
+}

src/backend/utils/cache/syscache.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/cache/syscache.c,v 1.123 2010/01/02 16:57:56 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/cache/syscache.c,v 1.124 2010/01/05 21:53:59 rhaas Exp $
  *
  * NOTES
  *	  These routines allow the parser/planner/executor to perform
@@ -43,6 +43,7 @@
 #include "catalog/pg_proc.h"
 #include "catalog/pg_rewrite.h"
 #include "catalog/pg_statistic.h"
+#include "catalog/pg_tablespace.h"
 #include "catalog/pg_ts_config.h"
 #include "catalog/pg_ts_config_map.h"
 #include "catalog/pg_ts_dict.h"
@@ -609,6 +610,18 @@ static const struct cachedesc cacheinfo[] = {
 		},
 		1024
 	},
+	{TableSpaceRelationId,		/* TABLESPACEOID */
+		TablespaceOidIndexId,
+		0,
+		1,
+		{
+			ObjectIdAttributeNumber,
+			0,
+			0,
+			0,
+		},
+		16
+	},
 	{TSConfigMapRelationId,		/* TSCONFIGMAP */
 		TSConfigMapIndexId,
 		0,