1 files changed, 173 insertions, 0 deletions
diff --git a/src/backend/access/table/tableamapi.c b/src/backend/access/table/tableamapi.c
new file mode 100644
index 00000000000..d49607e7f85
--- /dev/null
+++ b/src/backend/access/table/tableamapi.c
@@ -0,0 +1,173 @@
+/*----------------------------------------------------------------------
+ *
+ * tableamapi.c
+ *		Support routines for API for Postgres table access methods
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/backend/access/table/tableamapi.c
+ *----------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/heapam.h"
+#include "access/htup_details.h"
+#include "access/tableam.h"
+#include "access/xact.h"
+#include "catalog/pg_am.h"
+#include "catalog/pg_proc.h"
+#include "utils/fmgroids.h"
+#include "utils/memutils.h"
+#include "utils/syscache.h"
+
+
+static Oid	get_table_am_oid(const char *tableamname, bool missing_ok);
+
+
+/*
+ * GetTableAmRoutine
+ *		Call the specified access method handler routine to get its
+ *		TableAmRoutine struct, which will be palloc'd in the caller's
+ *		memory context.
+ */
+const TableAmRoutine *
+GetTableAmRoutine(Oid amhandler)
+{
+	Datum		datum;
+	const TableAmRoutine *routine;
+
+	datum = OidFunctionCall0(amhandler);
+	routine = (TableAmRoutine *) DatumGetPointer(datum);
+
+	if (routine == NULL || !IsA(routine, TableAmRoutine))
+		elog(ERROR, "Table access method handler %u did not return a TableAmRoutine struct",
+			 amhandler);
+
+	return routine;
+}
+
+/*
+ * GetTableAmRoutineByAmId - look up the handler of the table access
+ * method with the given OID, and get its TableAmRoutine struct.
+ */
+const TableAmRoutine *
+GetTableAmRoutineByAmId(Oid amoid)
+{
+	regproc		amhandler;
+	HeapTuple	tuple;
+	Form_pg_am	amform;
+
+	/* Get handler function OID for the access method */
+	tuple = SearchSysCache1(AMOID, ObjectIdGetDatum(amoid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for access method %u",
+			 amoid);
+	amform = (Form_pg_am) GETSTRUCT(tuple);
+
+	/* Check that it is a table access method */
+	if (amform->amtype != AMTYPE_TABLE)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("access method \"%s\" is not of type %s",
+						NameStr(amform->amname), "TABLE")));
+
+	amhandler = amform->amhandler;
+
+	/* Complain if handler OID is invalid */
+	if (!RegProcedureIsValid(amhandler))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("table access method \"%s\" does not have a handler",
+						NameStr(amform->amname))));
+
+	ReleaseSysCache(tuple);
+
+	/* And finally, call the handler function to get the API struct. */
+	return GetTableAmRoutine(amhandler);
+}
+
+/*
+ * get_table_am_oid - given a table access method name, look up the OID
+ *
+ * If missing_ok is false, throw an error if table access method name not
+ * found. If true, just return InvalidOid.
+ */
+static Oid
+get_table_am_oid(const char *tableamname, bool missing_ok)
+{
+	Oid			result;
+	Relation	rel;
+	HeapScanDesc scandesc;
+	HeapTuple	tuple;
+	ScanKeyData entry[1];
+
+	/*
+	 * Search pg_tablespace.  We use a heapscan here even though there is an
+	 * index on name, on the theory that pg_tablespace will usually have just
+	 * a few entries and so an indexed lookup is a waste of effort.
+	 */
+	rel = heap_open(AccessMethodRelationId, AccessShareLock);
+
+	ScanKeyInit(&entry[0],
+				Anum_pg_am_amname,
+				BTEqualStrategyNumber, F_NAMEEQ,
+				CStringGetDatum(tableamname));
+	scandesc = heap_beginscan_catalog(rel, 1, entry);
+	tuple = heap_getnext(scandesc, ForwardScanDirection);
+
+	/* We assume that there can be at most one matching tuple */
+	if (HeapTupleIsValid(tuple) &&
+		((Form_pg_am) GETSTRUCT(tuple))->amtype == AMTYPE_TABLE)
+		result = ((Form_pg_am) GETSTRUCT(tuple))->oid;
+	else
+		result = InvalidOid;
+
+	heap_endscan(scandesc);
+	heap_close(rel, AccessShareLock);
+
+	if (!OidIsValid(result) && !missing_ok)
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("table access method \"%s\" does not exist",
+						tableamname)));
+
+	return result;
+}
+
+/* check_hook: validate new default_table_access_method */
+bool
+check_default_table_access_method(char **newval, void **extra, GucSource source)
+{
+	/*
+	 * If we aren't inside a transaction, we cannot do database access so
+	 * cannot verify the name.  Must accept the value on faith.
+	 */
+	if (IsTransactionState())
+	{
+		if (**newval != '\0' &&
+			!OidIsValid(get_table_am_oid(*newval, true)))
+		{
+			/*
+			 * When source == PGC_S_TEST, don't throw a hard error for a
+			 * nonexistent table access method, only a NOTICE. See comments in
+			 * guc.h.
+			 */
+			if (source == PGC_S_TEST)
+			{
+				ereport(NOTICE,
+						(errcode(ERRCODE_UNDEFINED_OBJECT),
+						 errmsg("Table access method \"%s\" does not exist",
+								*newval)));
+			}
+			else
+			{
+				GUC_check_errdetail("Table access method \"%s\" does not exist.",
+									*newval);
+				return false;
+			}
+		}
+	}
+
+	return true;
+}