TABLESAMPLE, SQL Standard and extensible

Add a TABLESAMPLE clause to SELECT statements that allows
user to specify random BERNOULLI sampling or block level
SYSTEM sampling. Implementation allows for extensible
sampling functions to be written, using a standard API.
Basic version follows SQLStandard exactly. Usable
concrete use cases for the sampling API follow in later
commits.

Petr Jelinek

Reviewed by Michael Paquier and Simon Riggs

1 files changed, 27 insertions, 0 deletions

diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 1dc293297d9..f259751e157 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -32,6 +32,7 @@
 #include "catalog/pg_range.h"
 #include "catalog/pg_statistic.h"
 #include "catalog/pg_transform.h"
+#include "catalog/pg_tablesample_method.h"
 #include "catalog/pg_type.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -2996,3 +2997,29 @@ get_range_subtype(Oid rangeOid)
 	else
 		return InvalidOid;
 }
+
+/*				---------- PG_TABLESAMPLE_METHOD CACHE ----------			 */
+
+/*
+ * get_tablesample_method_name - given a tablesample method OID,
+ * look up the name or NULL if not found
+ */
+char *
+get_tablesample_method_name(Oid tsmid)
+{
+	HeapTuple	tuple;
+
+	tuple = SearchSysCache1(TABLESAMPLEMETHODOID, ObjectIdGetDatum(tsmid));
+	if (HeapTupleIsValid(tuple))
+	{
+		Form_pg_tablesample_method	tup =
+			(Form_pg_tablesample_method) GETSTRUCT(tuple);
+		char	   *result;
+
+		result = pstrdup(NameStr(tup->tsmname));
+		ReleaseSysCache(tuple);
+		return result;
+	}
+	else
+		return NULL;
+}