Split DDL processing into start and end hooks

The ProcessUtility hook doesn't give any information on applied DDL
commands, which makes it hard to implement DDL processing that
requires the result of a DDL command on a hypertable (for instance,
adding a constraint or index without an explicit name).

This change splits the DDL processing over start and end hooks,
handling DDL commands before and after regular PostgreSQL processing,
respectively.

The start DDL hook is still based on the ProcessUtility hook, while
the end DDL hook is based on an event trigger that allows getting
information on the created/dropped/altered objects.

Makefile

@@ -42,6 +42,7 @@ SRCS = \
 	src/cache.c \
 	src/cache_invalidate.c \
 	src/process_utility.c \
+	src/event_trigger.c \
 	src/trigger.c \
 	src/chunk.c \
 	src/scanner.c \

sql/ddl_triggers.sql

@@ -132,3 +132,8 @@ BEGIN
 END
 $BODY$;
 
+CREATE FUNCTION _timescaledb_internal.ddl_command_end() RETURNS event_trigger
+AS '$libdir/timescaledb', 'timescaledb_ddl_command_end' LANGUAGE C IMMUTABLE STRICT;
+
+CREATE EVENT TRIGGER timescaledb_ddl_command_end ON ddl_command_end
+EXECUTE PROCEDURE _timescaledb_internal.ddl_command_end();

src/event_trigger.c

@@ -0,0 +1,75 @@
+#include <postgres.h>
+#include <commands/event_trigger.h>
+#include <executor/executor.h>
+#include <access/htup_details.h>
+
+#include "event_trigger.h"
+
+/* Function manager info for the event "pg_event_trigger_ddl_commands", which is
+ * used to retrieve information on executed DDL commands in an event
+ * trigger. The function manager info is initialized on extension load. */
+static FmgrInfo ddl_commands_fmgrinfo;
+
+/*
+ * Get a list of executed DDL commands in an event trigger.
+ *
+ * This function calls the function pg_event_trigger_ddl_commands(), which is
+ * part of the event trigger API, and retrieves the DDL commands executed in
+ * relation to the event trigger. It is only valid to call this function from
+ * within an event trigger.
+ */
+List *
+event_trigger_ddl_commands(void)
+{
+	ReturnSetInfo rsinfo;
+	FunctionCallInfoData fcinfo;
+	TupleTableSlot *slot;
+	EState	   *estate = CreateExecutorState();
+	List	   *objects = NIL;
+
+	InitFunctionCallInfoData(fcinfo, &ddl_commands_fmgrinfo, 1, InvalidOid, NULL, NULL);
+	MemSet(&rsinfo, 0, sizeof(rsinfo));
+	rsinfo.type = T_ReturnSetInfo;
+	rsinfo.allowedModes = SFRM_Materialize;
+	rsinfo.econtext = CreateExprContext(estate);
+	fcinfo.resultinfo = (fmNodePtr) &rsinfo;
+
+	FunctionCallInvoke(&fcinfo);
+
+	slot = MakeSingleTupleTableSlot(rsinfo.setDesc);
+
+	while (tuplestore_gettupleslot(rsinfo.setResult, true, false, slot))
+	{
+		HeapTuple	tuple = ExecFetchSlotTuple(slot);
+		CollectedCommand *cmd;
+		Datum		values[rsinfo.setDesc->natts];
+		bool		nulls[rsinfo.setDesc->natts];
+
+		heap_deform_tuple(tuple, rsinfo.setDesc, values, nulls);
+
+		if (rsinfo.setDesc->natts > 8 && !nulls[8])
+		{
+			cmd = (CollectedCommand *) DatumGetPointer(values[8]);
+			objects = lappend(objects, cmd);
+		}
+	}
+
+	FreeExprContext(rsinfo.econtext, false);
+	FreeExecutorState(estate);
+	ExecDropSingleTupleTableSlot(slot);
+
+	return objects;
+}
+
+void
+_event_trigger_init(void)
+{
+	fmgr_info(fmgr_internal_function("pg_event_trigger_ddl_commands"),
+			  &ddl_commands_fmgrinfo);
+}
+
+void
+_event_trigger_fini(void)
+{
+	/* Nothing to do */
+}

src/event_trigger.h

@@ -0,0 +1,11 @@
+#ifndef TIMESCALEDB_EVENT_TRIGGER_H
+#define TIMESCALEDB_EVENT_TRIGGER_H
+
+#include <postgres.h>
+#include <nodes/pg_list.h>
+
+extern List *event_trigger_ddl_commands(void);
+extern void _event_trigger_init(void);
+extern void _event_trigger_fini(void);
+
+#endif   /* TIMESCALEDB_EVENT_TRIGGER_H */

src/hypertable.c

@@ -89,5 +89,7 @@ hypertable_relid(RangeVar *rv)
 bool
 is_hypertable(Oid relid)
 {
+	if (!OidIsValid(relid))
+		return false;
 	return hypertable_relid_lookup(relid) != InvalidOid;
 }

src/init.c

@@ -38,6 +38,9 @@ extern void _planner_fini(void);
 extern void _process_utility_init(void);
 extern void _process_utility_fini(void);
 
+extern void _event_trigger_init(void);
+extern void _event_trigger_fini(void);
+
 extern void _PG_init(void);
 extern void _PG_fini(void);
 
@@ -76,6 +79,7 @@ _PG_init(void)
 	_cache_invalidate_init();
 	_planner_init();
 	_executor_init();
+	_event_trigger_init();
 	_process_utility_init();
 	_guc_init();
 }
@@ -89,6 +93,7 @@ _PG_fini(void)
 	 */
 	_guc_fini();
 	_process_utility_fini();
+	_event_trigger_fini();
 	_executor_fini();
 	_planner_fini();
 	_cache_invalidate_fini();