Add sql_drop event for event triggers

This event takes place just before ddl_command_end, and is fired if and
only if at least one object has been dropped by the command.  (For
instance, DROP TABLE IF EXISTS of a table that does not in fact exist
will not lead to such a trigger firing).  Commands that drop multiple
objects (such as DROP SCHEMA or DROP OWNED BY) will cause a single event
to fire.  Some firings might be surprising, such as
ALTER TABLE DROP COLUMN.

The trigger is fired after the drop has taken place, because that has
been deemed the safest design, to avoid exposing possibly-inconsistent
internal state (system catalogs as well as current transaction) to the
user function code.  This means that careful tracking of object
identification is required during the object removal phase.

Like other currently existing events, there is support for tag
filtering.

To support the new event, add a new pg_event_trigger_dropped_objects()
set-returning function, which returns a set of rows comprising the
objects affected by the command.  This is to be used within the user
function code, and is mostly modelled after the recently introduced
pg_identify_object() function.

Catalog version bumped due to the new function.

Dimitri Fontaine and Álvaro Herrera
Review by Robert Haas, Tom Lane

13 files changed, 865 insertions, 110 deletions

diff --git a/src/backend/catalog/dependency.c b/src/backend/catalog/dependency.c
index ddf199049ef..286137c2513 100644
--- a/src/backend/catalog/dependency.c
+++ b/src/backend/catalog/dependency.c
@@ -191,6 +191,44 @@ static bool stack_address_present_add_flags(const ObjectAddress *object,
 
 
 /*
+ * Go through the objects given running the final actions on them, and execute
+ * the actual deletion.
+ */
+static void
+deleteObjectsInList(ObjectAddresses *targetObjects, Relation *depRel,
+					int flags)
+{
+	int		i;
+
+	/*
+	 * Keep track of objects for event triggers, if necessary.
+	 */
+	if (trackDroppedObjectsNeeded())
+	{
+		for (i = 0; i < targetObjects->numrefs; i++)
+		{
+			ObjectAddress *thisobj = targetObjects->refs + i;
+
+			if ((!(flags & PERFORM_DELETION_INTERNAL)) &&
+				EventTriggerSupportsObjectType(getObjectClass(thisobj)))
+			{
+				EventTriggerSQLDropAddObject(thisobj);
+			}
+		}
+	}
+
+	/*
+	 * Delete all the objects in the proper order.
+	 */
+	for (i = 0; i < targetObjects->numrefs; i++)
+	{
+		ObjectAddress *thisobj = targetObjects->refs + i;
+
+		deleteOneObject(thisobj, depRel, flags);
+	}
+}
+
+/*
  * performDeletion: attempt to drop the specified object.  If CASCADE
  * behavior is specified, also drop any dependent objects (recursively).
  * If RESTRICT behavior is specified, error out if there are any dependent
@@ -215,7 +253,6 @@ performDeletion(const ObjectAddress *object,
 {
 	Relation	depRel;
 	ObjectAddresses *targetObjects;
-	int			i;
 
 	/*
 	 * We save some cycles by opening pg_depend just once and passing the
@@ -250,15 +287,8 @@ performDeletion(const ObjectAddress *object,
 						   NOTICE,
 						   object);
 
-	/*
-	 * Delete all the objects in the proper order.
-	 */
-	for (i = 0; i < targetObjects->numrefs; i++)
-	{
-		ObjectAddress *thisobj = targetObjects->refs + i;
-
-		deleteOneObject(thisobj, &depRel, flags);
-	}
+	/* do the deed */
+	deleteObjectsInList(targetObjects, &depRel, flags);
 
 	/* And clean up */
 	free_object_addresses(targetObjects);
@@ -332,15 +362,8 @@ performMultipleDeletions(const ObjectAddresses *objects,
 						   NOTICE,
 						   (objects->numrefs == 1 ? objects->refs : NULL));
 
-	/*
-	 * Delete all the objects in the proper order.
-	 */
-	for (i = 0; i < targetObjects->numrefs; i++)
-	{
-		ObjectAddress *thisobj = targetObjects->refs + i;
-
-		deleteOneObject(thisobj, &depRel, flags);
-	}
+	/* do the deed */
+	deleteObjectsInList(targetObjects, &depRel, flags);
 
 	/* And clean up */
 	free_object_addresses(targetObjects);
@@ -356,6 +379,10 @@ performMultipleDeletions(const ObjectAddresses *objects,
  * This is currently used only to clean out the contents of a schema
  * (namespace): the passed object is a namespace.  We normally want this
  * to be done silently, so there's an option to suppress NOTICE messages.
+ *
+ * Note we don't fire object drop event triggers here; it would be wrong to do
+ * so for the current only use of this function, but if more callers are added
+ * this might need to be reconsidered.
  */
 void
 deleteWhatDependsOn(const ObjectAddress *object,
diff --git a/src/backend/commands/event_trigger.c b/src/backend/commands/event_trigger.c
index fbe8f49a9e7..ed5240d63b0 100644
--- a/src/backend/commands/event_trigger.c
+++ b/src/backend/commands/event_trigger.c
@@ -19,14 +19,17 @@
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_event_trigger.h"
+#include "catalog/pg_namespace.h"
 #include "catalog/pg_proc.h"
 #include "catalog/pg_trigger.h"
 #include "catalog/pg_type.h"
 #include "commands/dbcommands.h"
 #include "commands/event_trigger.h"
 #include "commands/trigger.h"
+#include "funcapi.h"
 #include "parser/parse_func.h"
 #include "pgstat.h"
+#include "lib/ilist.h"
 #include "miscadmin.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
@@ -39,6 +42,17 @@
 #include "utils/syscache.h"
 #include "tcop/utility.h"
 
+
+typedef struct EventTriggerQueryState
+{
+	slist_head	SQLDropList;
+	bool		in_sql_drop;
+	MemoryContext	cxt;
+	struct EventTriggerQueryState *previous;
+} EventTriggerQueryState;
+
+EventTriggerQueryState	*currentEventTriggerState = NULL;
+
 typedef struct
 {
 	const char	   *obtypename;
@@ -89,6 +103,17 @@ static event_trigger_support_data event_trigger_support[] = {
 	{ NULL, false }
 };
 
+/* Support for dropped objects */
+typedef struct SQLDropObject
+{
+	ObjectAddress	address;
+	const char	   *schemaname;
+	const char	   *objname;
+	const char	   *objidentity;
+	const char	   *objecttype;
+	slist_node		next;
+} SQLDropObject;
+
 static void AlterEventTriggerOwner_internal(Relation rel,
 											HeapTuple tup,
 											Oid newOwnerId);
@@ -127,7 +152,8 @@ CreateEventTrigger(CreateEventTrigStmt *stmt)
 
 	/* Validate event name. */
 	if (strcmp(stmt->eventname, "ddl_command_start") != 0 &&
-		strcmp(stmt->eventname, "ddl_command_end") != 0)
+		strcmp(stmt->eventname, "ddl_command_end") != 0 &&
+		strcmp(stmt->eventname, "sql_drop") != 0)
 		ereport(ERROR,
 			(errcode(ERRCODE_SYNTAX_ERROR),
 			 errmsg("unrecognized event name \"%s\"",
@@ -151,7 +177,10 @@ CreateEventTrigger(CreateEventTrigStmt *stmt)
 	}
 
 	/* Validate tag list, if any. */
-	if (strcmp(stmt->eventname, "ddl_command_start") == 0 && tags != NULL)
+	if ((strcmp(stmt->eventname, "ddl_command_start") == 0 ||
+		 strcmp(stmt->eventname, "ddl_command_end") == 0 ||
+		 strcmp(stmt->eventname, "sql_drop") == 0)
+		&& tags != NULL)
 		validate_ddl_tags("tag", tags);
 
 	/*
@@ -220,7 +249,8 @@ check_ddl_tag(const char *tag)
 		pg_strcasecmp(tag, "SELECT INTO") == 0 ||
 		pg_strcasecmp(tag, "REFRESH MATERIALIZED VIEW") == 0 ||
 		pg_strcasecmp(tag, "ALTER DEFAULT PRIVILEGES") == 0 ||
-		pg_strcasecmp(tag, "ALTER LARGE OBJECT") == 0)
+		pg_strcasecmp(tag, "ALTER LARGE OBJECT") == 0 ||
+		pg_strcasecmp(tag, "DROP OWNED") == 0)
 		return EVENT_TRIGGER_COMMAND_TAG_OK;
 
 	/*
@@ -568,35 +598,19 @@ filter_event_trigger(const char **tag, EventTriggerCacheItem  *item)
 }
 
 /*
- * Fire ddl_command_start triggers.
+ * Setup for running triggers for the given event.  Return value is an OID list
+ * of functions to run; if there are any, trigdata is filled with an
+ * appropriate EventTriggerData for them to receive.
  */
-void
-EventTriggerDDLCommandStart(Node *parsetree)
+static List *
+EventTriggerCommonSetup(Node *parsetree,
+						EventTriggerEvent event, const char *eventstr,
+						EventTriggerData *trigdata)
 {
+	const char *tag;
 	List	   *cachelist;
-	List	   *runlist = NIL;
 	ListCell   *lc;
-	const char *tag;
-	EventTriggerData	trigdata;
-
-	/*
-	 * Event Triggers are completely disabled in standalone mode.  There are
-	 * (at least) two reasons for this:
-	 *
-	 * 1. A sufficiently broken event trigger might not only render the
-	 * database unusable, but prevent disabling itself to fix the situation.
-	 * In this scenario, restarting in standalone mode provides an escape
-	 * hatch.
-	 *
-	 * 2. BuildEventTriggerCache relies on systable_beginscan_ordered, and
-	 * therefore will malfunction if pg_event_trigger's indexes are damaged.
-	 * To allow recovery from a damaged index, we need some operating mode
-	 * wherein event triggers are disabled.  (Or we could implement
-	 * heapscan-and-sort logic for that case, but having disaster recovery
-	 * scenarios depend on code that's otherwise untested isn't appetizing.)
-	 */
-	if (!IsUnderPostmaster)
-		return;
+	List	   *runlist = NIL;
 
 	/*
 	 * We want the list of command tags for which this procedure is actually
@@ -624,9 +638,9 @@ EventTriggerDDLCommandStart(Node *parsetree)
 #endif
 
 	/* Use cache to find triggers for this event; fast exit if none. */
-	cachelist = EventCacheLookup(EVT_DDLCommandStart);
-	if (cachelist == NULL)
-		return;
+	cachelist = EventCacheLookup(event);
+	if (cachelist == NIL)
+		return NIL;
 
 	/* Get the command tag. */
 	tag = CreateCommandTag(parsetree);
@@ -649,11 +663,51 @@ EventTriggerDDLCommandStart(Node *parsetree)
 		}
 	}
 
-	/* Construct event trigger data. */
-	trigdata.type = T_EventTriggerData;
-	trigdata.event = "ddl_command_start";
-	trigdata.parsetree = parsetree;
-	trigdata.tag = tag;
+	/* don't spend any more time on this if no functions to run */
+	if (runlist == NIL)
+		return NIL;
+
+	trigdata->type = T_EventTriggerData;
+	trigdata->event = eventstr;
+	trigdata->parsetree = parsetree;
+	trigdata->tag = tag;
+
+	return runlist;
+}
+
+/*
+ * Fire ddl_command_start triggers.
+ */
+void
+EventTriggerDDLCommandStart(Node *parsetree)
+{
+	List	   *runlist;
+	EventTriggerData	trigdata;
+
+	/*
+	 * Event Triggers are completely disabled in standalone mode.  There are
+	 * (at least) two reasons for this:
+	 *
+	 * 1. A sufficiently broken event trigger might not only render the
+	 * database unusable, but prevent disabling itself to fix the situation.
+	 * In this scenario, restarting in standalone mode provides an escape
+	 * hatch.
+	 *
+	 * 2. BuildEventTriggerCache relies on systable_beginscan_ordered, and
+	 * therefore will malfunction if pg_event_trigger's indexes are damaged.
+	 * To allow recovery from a damaged index, we need some operating mode
+	 * wherein event triggers are disabled.  (Or we could implement
+	 * heapscan-and-sort logic for that case, but having disaster recovery
+	 * scenarios depend on code that's otherwise untested isn't appetizing.)
+	 */
+	if (!IsUnderPostmaster)
+		return;
+
+	runlist = EventTriggerCommonSetup(parsetree,
+									  EVT_DDLCommandStart, "ddl_command_start",
+									  &trigdata);
+	if (runlist == NIL)
+		return;
 
 	/* Run the triggers. */
 	EventTriggerInvoke(runlist, &trigdata);
@@ -674,10 +728,7 @@ EventTriggerDDLCommandStart(Node *parsetree)
 void
 EventTriggerDDLCommandEnd(Node *parsetree)
 {
-	List	   *cachelist;
-	List	   *runlist = NIL;
-	ListCell   *lc;
-	const char *tag;
+	List	   *runlist;
 	EventTriggerData	trigdata;
 
 	/*
@@ -687,53 +738,61 @@ EventTriggerDDLCommandEnd(Node *parsetree)
 	if (!IsUnderPostmaster)
 		return;
 
+	runlist = EventTriggerCommonSetup(parsetree,
+									  EVT_DDLCommandEnd, "ddl_command_end",
+									  &trigdata);
+	if (runlist == NIL)
+		return;
+
 	/*
-	 * See EventTriggerDDLCommandStart for a discussion about why this check is
-	 * important.
-	 *
+	 * Make sure anything the main command did will be visible to the
+	 * event triggers.
 	 */
-#ifdef USE_ASSERT_CHECKING
-	if (assert_enabled)
-	{
-		const char *dbgtag;
+	CommandCounterIncrement();
 
-		dbgtag = CreateCommandTag(parsetree);
-		if (check_ddl_tag(dbgtag) != EVENT_TRIGGER_COMMAND_TAG_OK)
-			elog(ERROR, "unexpected command tag \"%s\"", dbgtag);
-	}
-#endif
+	/* Run the triggers. */
+	EventTriggerInvoke(runlist, &trigdata);
 
-	/* Use cache to find triggers for this event; fast exit if none. */
-	cachelist = EventCacheLookup(EVT_DDLCommandEnd);
-	if (cachelist == NULL)
-		return;
+	/* Cleanup. */
+	list_free(runlist);
+}
 
-	/* Get the command tag. */
-	tag = CreateCommandTag(parsetree);
+/*
+ * Fire sql_drop triggers.
+ */
+void
+EventTriggerSQLDrop(Node *parsetree)
+{
+	List	   *runlist;
+	EventTriggerData	trigdata;
 
 	/*
-	 * Filter list of event triggers by command tag, and copy them into
-	 * our memory context.  Once we start running the command trigers, or
-	 * indeed once we do anything at all that touches the catalogs, an
-	 * invalidation might leave cachelist pointing at garbage, so we must
-	 * do this before we can do much else.
+	 * See EventTriggerDDLCommandStart for a discussion about why event
+	 * triggers are disabled in single user mode.
 	 */
-	foreach (lc, cachelist)
-	{
-		EventTriggerCacheItem  *item = lfirst(lc);
+	if (!IsUnderPostmaster)
+		return;
 
-		if (filter_event_trigger(&tag, item))
-		{
-			/* We must plan to fire this trigger. */
-			runlist = lappend_oid(runlist, item->fnoid);
-		}
-	}
+	/*
+	 * Use current state to determine whether this event fires at all.  If there
+	 * are no triggers for the sql_drop event, then we don't have anything to do
+	 * here.  Note that dropped object collection is disabled if this is the case,
+	 * so even if we were to try to run, the list would be empty.
+	 */
+	if (!currentEventTriggerState ||
+		slist_is_empty(&currentEventTriggerState->SQLDropList))
+		return;
 
-	/* Construct event trigger data. */
-	trigdata.type = T_EventTriggerData;
-	trigdata.event = "ddl_command_end";
-	trigdata.parsetree = parsetree;
-	trigdata.tag = tag;
+	runlist = EventTriggerCommonSetup(parsetree,
+									  EVT_SQLDrop, "sql_drop",
+									  &trigdata);
+	/*
+	 * Nothing to do if run list is empty.  Note this shouldn't happen, because
+	 * if there are no sql_drop events, then objects-to-drop wouldn't have been
+	 * collected in the first place and we would have quitted above.
+	 */
+	if (runlist == NIL)
+		return;
 
 	/*
 	 * Make sure anything the main command did will be visible to the
@@ -741,8 +800,27 @@ EventTriggerDDLCommandEnd(Node *parsetree)
 	 */
 	CommandCounterIncrement();
 
+	/*
+	 * Make sure pg_event_trigger_dropped_objects only works when running these
+	 * triggers.  Use PG_TRY to ensure in_sql_drop is reset even when one
+	 * trigger fails.  (This is perhaps not necessary, as the currentState
+	 * variable will be removed shortly by our caller, but it seems better to
+	 * play safe.)
+	 */
+	currentEventTriggerState->in_sql_drop = true;
+
 	/* Run the triggers. */
-	EventTriggerInvoke(runlist, &trigdata);
+	PG_TRY();
+	{
+		EventTriggerInvoke(runlist, &trigdata);
+	}
+	PG_CATCH();
+	{
+		currentEventTriggerState->in_sql_drop = false;
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+	currentEventTriggerState->in_sql_drop = false;
 
 	/* Cleanup. */
 	list_free(runlist);
@@ -832,3 +910,287 @@ EventTriggerSupportsObjectType(ObjectType obtype)
 	}
 	return true;
 }
+
+/*
+ * Prepare event trigger state for a new complete query to run, if necessary;
+ * returns whether this was done.  If it was, EventTriggerEndCompleteQuery must
+ * be called when the query is done, regardless of whether it succeeds or fails
+ * -- so use of a PG_TRY block is mandatory.
+ */
+bool
+EventTriggerBeginCompleteQuery(void)
+{
+	EventTriggerQueryState *state;
+	MemoryContext	cxt;
+
+	/*
+	 * Currently, sql_drop events are the only reason to have event trigger
+	 * state at all; so if there are none, don't install one.
+	 */
+	if (!trackDroppedObjectsNeeded())
+		return false;
+
+	cxt = AllocSetContextCreate(TopMemoryContext,
+								"event trigger state",
+								ALLOCSET_DEFAULT_MINSIZE,
+								ALLOCSET_DEFAULT_INITSIZE,
+								ALLOCSET_DEFAULT_MAXSIZE);
+	state = MemoryContextAlloc(cxt, sizeof(EventTriggerQueryState));
+	state->cxt = cxt;
+	slist_init(&(state->SQLDropList));
+	state->in_sql_drop = false;
+
+	state->previous = currentEventTriggerState;
+	currentEventTriggerState = state;
+
+	return true;
+}
+
+/*
+ * Query completed (or errored out) -- clean up local state, return to previous
+ * one.
+ *
+ * Note: it's an error to call this routine if EventTriggerBeginCompleteQuery
+ * returned false previously.
+ *
+ * Note: this might be called in the PG_CATCH block of a failing transaction,
+ * so be wary of running anything unnecessary.  (In particular, it's probably
+ * unwise to try to allocate memory.)
+ */
+void
+EventTriggerEndCompleteQuery(void)
+{
+	EventTriggerQueryState *prevstate;
+
+	prevstate = currentEventTriggerState->previous;
+
+	/* this avoids the need for retail pfree of SQLDropList items: */
+	MemoryContextDelete(currentEventTriggerState->cxt);
+
+	currentEventTriggerState = prevstate;
+}
+
+/*
+ * Do we need to keep close track of objects being dropped?
+ *
+ * This is useful because there is a cost to running with them enabled.
+ */
+bool
+trackDroppedObjectsNeeded(void)
+{
+	/* true if any sql_drop event trigger exists */
+	return list_length(EventCacheLookup(EVT_SQLDrop)) > 0;
+}
+
+/*
+ * Support for dropped objects information on event trigger functions.
+ *
+ * We keep the list of objects dropped by the current command in current
+ * state's SQLDropList (comprising SQLDropObject items).  Each time a new
+ * command is to start, a clean EventTriggerQueryState is created; commands
+ * that drop objects do the dependency.c dance to drop objects, which
+ * populates the current state's SQLDropList; when the event triggers are
+ * invoked they can consume the list via pg_event_trigger_dropped_objects().
+ * When the command finishes, the EventTriggerQueryState is cleared, and
+ * the one from the previous command is restored (when no command is in
+ * execution, the current state is NULL).
+ *
+ * All this lets us support the case that an event trigger function drops
+ * objects "reentrantly".
+ */
+
+/*
+ * Register one object as being dropped by the current command.
+ */
+void
+EventTriggerSQLDropAddObject(ObjectAddress *object)
+{
+	SQLDropObject  *obj;
+	MemoryContext	oldcxt;
+
+	if (!currentEventTriggerState)
+		return;
+
+	Assert(EventTriggerSupportsObjectType(getObjectClass(object)));
+
+	/* don't report temp schemas */
+	if (object->classId == NamespaceRelationId &&
+		isAnyTempNamespace(object->objectId))
+		return;
+
+	oldcxt = MemoryContextSwitchTo(currentEventTriggerState->cxt);
+
+	obj = palloc0(sizeof(SQLDropObject));
+	obj->address = *object;
+
+	/*
+	 * Obtain schema names from the object's catalog tuple, if one exists;
+	 * this lets us skip objects in temp schemas.  We trust that ObjectProperty
+	 * contains all object classes that can be schema-qualified.
+	 */
+	if (is_objectclass_supported(object->classId))
+	{
+		Relation	catalog;
+		HeapTuple	tuple;
+
+		catalog = heap_open(obj->address.classId, AccessShareLock);
+		tuple = get_catalog_object_by_oid(catalog, obj->address.objectId);
+
+		if (tuple)
+		{
+			AttrNumber	attnum;
+			Datum		datum;
+			bool		isnull;
+
+			attnum = get_object_attnum_namespace(obj->address.classId);
+			if (attnum != InvalidAttrNumber)
+			{
+				datum = heap_getattr(tuple, attnum,
+									 RelationGetDescr(catalog), &isnull);
+				if (!isnull)
+				{
+					Oid		namespaceId;
+
+					namespaceId = DatumGetObjectId(datum);
+					/* Don't report objects in temp namespaces */
+					if (isAnyTempNamespace(namespaceId))
+					{
+						pfree(obj);
+						heap_close(catalog, AccessShareLock);
+						MemoryContextSwitchTo(oldcxt);
+						return;
+					}
+
+					obj->schemaname = get_namespace_name(namespaceId);
+				}
+			}
+
+			if (get_object_namensp_unique(obj->address.classId) &&
+				obj->address.objectSubId == 0)
+			{
+				attnum = get_object_attnum_name(obj->address.classId);
+				if (attnum != InvalidAttrNumber)
+				{
+					datum = heap_getattr(tuple, attnum,
+										 RelationGetDescr(catalog), &isnull);
+					if (!isnull)
+						obj->objname = pstrdup(NameStr(*DatumGetName(datum)));
+				}
+			}
+		}
+
+		heap_close(catalog, AccessShareLock);
+	}
+
+	/* object identity */
+	obj->objidentity = getObjectIdentity(&obj->address);
+
+	/* and object type, too */
+	obj->objecttype = getObjectTypeDescription(&obj->address);
+
+	slist_push_head(&(currentEventTriggerState->SQLDropList), &obj->next);
+
+	MemoryContextSwitchTo(oldcxt);
+}
+
+/*
+ * pg_event_trigger_dropped_objects
+ *
+ * Make the list of dropped objects available to the user function run by the
+ * Event Trigger.
+ */
+Datum
+pg_event_trigger_dropped_objects(PG_FUNCTION_ARGS)
+{
+	ReturnSetInfo	   *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc			tupdesc;
+	Tuplestorestate	   *tupstore;
+	MemoryContext		per_query_ctx;
+	MemoryContext		oldcontext;
+	slist_iter			iter;
+
+	/*
+	 * Protect this function from being called out of context
+	 */
+	if (!currentEventTriggerState ||
+		!currentEventTriggerState->in_sql_drop)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("%s can only be called in a sql_drop event trigger function",
+						"pg_event_trigger_dropped_objects()")));
+
+	/* check to see if caller supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	/* Build tuplestore to hold the result rows */
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	slist_foreach(iter, &(currentEventTriggerState->SQLDropList))
+	{
+		SQLDropObject *obj;
+		int			i = 0;
+		Datum		values[7];
+		bool		nulls[7];
+
+		obj = slist_container(SQLDropObject, next, iter.cur);
+
+		MemSet(values, 0, sizeof(values));
+		MemSet(nulls, 0, sizeof(nulls));
+
+		/* classid */
+		values[i++] = ObjectIdGetDatum(obj->address.classId);
+
+		/* objid */
+		values[i++] = ObjectIdGetDatum(obj->address.objectId);
+
+		/* objsubid */
+		values[i++] = Int32GetDatum(obj->address.objectSubId);
+
+		/* object_type */
+		values[i++] = CStringGetTextDatum(obj->objecttype);
+
+		/* schema_name */
+		if (obj->schemaname)
+			values[i++] = CStringGetTextDatum(obj->schemaname);
+		else
+			nulls[i++] = true;
+
+		/* object_name */
+		if (obj->objname)
+			values[i++] = CStringGetTextDatum(obj->objname);
+		else
+			nulls[i++] = true;
+
+		/* object_identity */
+		if (obj->objidentity)
+			values[i++] = CStringGetTextDatum(obj->objidentity);
+		else
+			nulls[i++] = true;
+
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+	}
+
+	/* clean up and return the tuplestore */
+	tuplestore_donestoring(tupstore);
+
+	return (Datum) 0;
+}
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 0d82141fef6..ed8502c6e4e 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4478,7 +4478,6 @@ DropTrigStmt:
  *
  *		QUERIES :
  *				CREATE EVENT TRIGGER ...
- *				DROP EVENT TRIGGER ...
  *				ALTER EVENT TRIGGER ...
  *
  *****************************************************************************/
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index a1c03f1f763..77b4e5368e7 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -346,12 +346,13 @@ ProcessUtility(Node *parsetree,
 	do { \
 	    if (isCompleteQuery) \
         { \
-		    EventTriggerDDLCommandStart(parsetree); \
+			EventTriggerDDLCommandStart(parsetree); \
 		} \
 		fncall; \
         if (isCompleteQuery) \
         { \
-		    EventTriggerDDLCommandEnd(parsetree); \
+			EventTriggerSQLDrop(parsetree); \
+			EventTriggerDDLCommandEnd(parsetree); \
 		} \
 	} while (0)
 
@@ -366,10 +367,48 @@ ProcessUtility(Node *parsetree,
 		fncall; \
 		if (_supported) \
 		{ \
+			EventTriggerSQLDrop(parsetree); \
 			EventTriggerDDLCommandEnd(parsetree); \
 		} \
 	} while (0)
 
+/*
+ * UTILITY_BEGIN_QUERY and UTILITY_END_QUERY are a pair of macros to enclose
+ * execution of a single DDL command, to ensure the event trigger environment
+ * is appropriately set up before starting, and tore down after completion or
+ * error.
+ */
+#define UTILITY_BEGIN_QUERY(isComplete) \
+	do { \
+		bool		_needCleanup = false; \
+		\
+		if (isComplete) \
+		{ \
+			_needCleanup = EventTriggerBeginCompleteQuery(); \
+		} \
+		\
+		PG_TRY(); \
+		{ \
+			/* avoid empty statement when followed by a semicolon */ \
+			(void) 0
+
+#define UTILITY_END_QUERY() \
+		} \
+		PG_CATCH(); \
+		{ \
+			if (_needCleanup) \
+			{ \
+				EventTriggerEndCompleteQuery(); \
+			} \
+			PG_RE_THROW(); \
+		} \
+		PG_END_TRY(); \
+		if (_needCleanup) \
+		{ \
+			EventTriggerEndCompleteQuery(); \
+		} \
+	} while (0)
+
 void
 standard_ProcessUtility(Node *parsetree,
 						const char *queryString,
@@ -386,6 +425,8 @@ standard_ProcessUtility(Node *parsetree,
 	if (completionTag)
 		completionTag[0] = '\0';
 
+	UTILITY_BEGIN_QUERY(isCompleteQuery);
+
 	switch (nodeTag(parsetree))
 	{
 			/*
@@ -615,7 +656,10 @@ standard_ProcessUtility(Node *parsetree,
 				}
 
 				if (isCompleteQuery)
+				{
+					EventTriggerSQLDrop(parsetree);
 					EventTriggerDDLCommandEnd(parsetree);
+				}
 			}
 			break;
 
@@ -726,7 +770,10 @@ standard_ProcessUtility(Node *parsetree,
 
 				if (isCompleteQuery
 					&& EventTriggerSupportsObjectType(stmt->removeType))
+				{
+					EventTriggerSQLDrop(parsetree);
 					EventTriggerDDLCommandEnd(parsetree);
+				}
 
 				break;
 			}
@@ -856,6 +903,12 @@ standard_ProcessUtility(Node *parsetree,
 					ereport(NOTICE,
 						  (errmsg("relation \"%s\" does not exist, skipping",
 								  atstmt->relation->relname)));
+
+				if (isCompleteQuery)
+				{
+					EventTriggerSQLDrop(parsetree);
+					EventTriggerDDLCommandEnd(parsetree);
+				}
 			}
 			break;
 
@@ -1248,8 +1301,9 @@ standard_ProcessUtility(Node *parsetree,
 			break;
 
 		case T_DropOwnedStmt:
-			/* no event triggers for global objects */
-			DropOwnedObjects((DropOwnedStmt *) parsetree);
+			InvokeDDLCommandEventTriggers(
+				parsetree,
+				DropOwnedObjects((DropOwnedStmt *) parsetree));
 			break;
 
 		case T_ReassignOwnedStmt:
@@ -1372,6 +1426,8 @@ standard_ProcessUtility(Node *parsetree,
 				 (int) nodeTag(parsetree));
 			break;
 	}
+
+	UTILITY_END_QUERY();
 }
 
 /*
diff --git a/src/backend/utils/adt/regproc.c b/src/backend/utils/adt/regproc.c
index 94599aa44ba..700247e4741 100644
--- a/src/backend/utils/adt/regproc.c
+++ b/src/backend/utils/adt/regproc.c
@@ -345,7 +345,7 @@ format_procedure_internal(Oid procedure_oid, bool force_qualify)
 
 		/*
 		 * Would this proc be found (given the right args) by regprocedurein?
-		 * If not, we need to qualify it.
+		 * If not, or if caller requests it, we need to qualify it.
 		 */
 		if (!force_qualify && FunctionIsVisible(procedure_oid))
 			nspname = NULL;
diff --git a/src/backend/utils/cache/evtcache.c b/src/backend/utils/cache/evtcache.c
index 34c61280c27..bbd3ae369d3 100644
--- a/src/backend/utils/cache/evtcache.c
+++ b/src/backend/utils/cache/evtcache.c
@@ -169,6 +169,8 @@ BuildEventTriggerCache(void)
 			event = EVT_DDLCommandStart;
 		else if (strcmp(evtevent, "ddl_command_end") == 0)
 			event = EVT_DDLCommandEnd;
+		else if (strcmp(evtevent, "sql_drop") == 0)
+			event = EVT_SQLDrop;
 		else
 			continue;
 
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index cbc4673d1b4..0eb8eefb8ff 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201303201
+#define CATALOG_VERSION_NO	201303271
 
 #endif
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 4aee00233a9..151987ec1d3 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -4693,6 +4693,9 @@ DATA(insert OID = 3473 (  spg_range_quad_leaf_consistent	PGNSP PGUID 12 1 0 0 0
 DESCR("SP-GiST support for quad tree over range");
 
 
+/* event triggers */
+DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s 0 0 2249 "" "{26,26,23,25,25,25,25}" "{o,o,o,o,o,o,o}" "{classid, objid, objsubid, object_type, schema_name, object_name, object_identity}" _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
+DESCR("list objects dropped by the current command");
 /*
  * Symbolic values for provolatile column: these indicate whether the result
  * of a function is dependent *only* on the values of its explicit arguments,
diff --git a/src/include/commands/event_trigger.h b/src/include/commands/event_trigger.h
index 74c150bd084..8ea99c19c99 100644
--- a/src/include/commands/event_trigger.h
+++ b/src/include/commands/event_trigger.h
@@ -13,13 +13,14 @@
 #ifndef EVENT_TRIGGER_H
 #define EVENT_TRIGGER_H
 
+#include "catalog/objectaddress.h"
 #include "catalog/pg_event_trigger.h"
 #include "nodes/parsenodes.h"
 
 typedef struct EventTriggerData
 {
 	NodeTag		type;
-	char	   *event;				/* event name */
+	const char *event;				/* event name */
 	Node	   *parsetree;			/* parse tree */
 	const char *tag;				/* command tag */
 } EventTriggerData;
@@ -42,5 +43,11 @@ extern void AlterEventTriggerOwner_oid(Oid, Oid newOwnerId);
 extern bool EventTriggerSupportsObjectType(ObjectType obtype);
 extern void EventTriggerDDLCommandStart(Node *parsetree);
 extern void EventTriggerDDLCommandEnd(Node *parsetree);
+extern void EventTriggerSQLDrop(Node *parsetree);
+
+extern bool EventTriggerBeginCompleteQuery(void);
+extern void EventTriggerEndCompleteQuery(void);
+extern bool trackDroppedObjectsNeeded(void);
+extern void EventTriggerSQLDropAddObject(ObjectAddress *object);
 
 #endif   /* EVENT_TRIGGER_H */
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index cd8ac9462b5..e71876502e1 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -1151,6 +1151,9 @@ extern Datum pg_identify_object(PG_FUNCTION_ARGS);
 /* commands/constraint.c */
 extern Datum unique_key_recheck(PG_FUNCTION_ARGS);
 
+/* commands/event_trigger.c */
+extern Datum pg_event_trigger_dropped_objects(PG_FUNCTION_ARGS);
+
 /* commands/extension.c */
 extern Datum pg_available_extensions(PG_FUNCTION_ARGS);
 extern Datum pg_available_extension_versions(PG_FUNCTION_ARGS);
diff --git a/src/include/utils/evtcache.h b/src/include/utils/evtcache.h
index c230995212d..945e5b53cb8 100644
--- a/src/include/utils/evtcache.h
+++ b/src/include/utils/evtcache.h
@@ -19,7 +19,8 @@
 typedef enum
 {
 	EVT_DDLCommandStart,
-	EVT_DDLCommandEnd
+	EVT_DDLCommandEnd,
+	EVT_SQLDrop
 } EventTriggerEvent;
 
 typedef struct
diff --git a/src/test/regress/expected/event_trigger.out b/src/test/regress/expected/event_trigger.out
index bf020de16f6..060cd722bef 100644
--- a/src/test/regress/expected/event_trigger.out
+++ b/src/test/regress/expected/event_trigger.out
@@ -93,11 +93,204 @@ ERROR:  event trigger "regress_event_trigger" does not exist
 drop role regression_bob;
 ERROR:  role "regression_bob" cannot be dropped because some objects depend on it
 DETAIL:  owner of event trigger regress_event_trigger3
+-- cleanup before next test
 -- these are all OK; the second one should emit a NOTICE
 drop event trigger if exists regress_event_trigger2;
 drop event trigger if exists regress_event_trigger2;
 NOTICE:  event trigger "regress_event_trigger2" does not exist, skipping
 drop event trigger regress_event_trigger3;
 drop event trigger regress_event_trigger_end;
-drop function test_event_trigger();
-drop role regression_bob;
+-- test support for dropped objects
+CREATE SCHEMA schema_one authorization regression_bob;
+CREATE SCHEMA schema_two authorization regression_bob;
+CREATE SCHEMA audit_tbls authorization regression_bob;
+SET SESSION AUTHORIZATION regression_bob;
+CREATE TABLE schema_one.table_one(a int);
+CREATE TABLE schema_one."table two"(a int);
+CREATE TABLE schema_one.table_three(a int);
+CREATE TABLE audit_tbls.schema_one_table_two(the_value text);
+CREATE TABLE schema_two.table_two(a int);
+CREATE TABLE schema_two.table_three(a int, b text);
+CREATE TABLE audit_tbls.schema_two_table_three(the_value text);
+CREATE OR REPLACE FUNCTION schema_two.add(int, int) RETURNS int LANGUAGE plpgsql
+  CALLED ON NULL INPUT
+  AS $$ BEGIN RETURN coalesce($1,0) + coalesce($2,0); END; $$;
+CREATE AGGREGATE schema_two.newton
+  (BASETYPE = int, SFUNC = schema_two.add, STYPE = int);
+RESET SESSION AUTHORIZATION;
+CREATE TABLE undroppable_objs (
+	object_type text,
+	object_identity text
+);
+INSERT INTO undroppable_objs VALUES
+('table', 'schema_one.table_three'),
+('table', 'audit_tbls.schema_two_table_three');
+CREATE TABLE dropped_objects (
+	type text,
+	schema text,
+	object text
+);
+-- This tests errors raised within event triggers; the one in audit_tbls
+-- uses 2nd-level recursive invocation via test_evtrig_dropped_objects().
+CREATE OR REPLACE FUNCTION undroppable() RETURNS event_trigger
+LANGUAGE plpgsql AS $$
+DECLARE
+	obj record;
+BEGIN
+	PERFORM 1 FROM pg_tables WHERE tablename = 'undroppable_objs';
+	IF NOT FOUND THEN
+		RAISE NOTICE 'table undroppable_objs not found, skipping';
+		RETURN;
+	END IF;
+	FOR obj IN
+		SELECT * FROM pg_event_trigger_dropped_objects() JOIN
+			undroppable_objs USING (object_type, object_identity)
+	LOOP
+		RAISE EXCEPTION 'object % of type % cannot be dropped',
+			obj.object_identity, obj.object_type;
+	END LOOP;
+END;
+$$;
+CREATE EVENT TRIGGER undroppable ON sql_drop
+	EXECUTE PROCEDURE undroppable();
+CREATE OR REPLACE FUNCTION test_evtrig_dropped_objects() RETURNS event_trigger
+LANGUAGE plpgsql AS $$
+DECLARE
+    obj record;
+BEGIN
+    FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
+    LOOP
+        IF obj.object_type = 'table' THEN
+                EXECUTE format('DROP TABLE IF EXISTS audit_tbls.%I',
+					format('%s_%s', obj.schema_name, obj.object_name));
+        END IF;
+
+	INSERT INTO dropped_objects
+		(type, schema, object) VALUES
+		(obj.object_type, obj.schema_name, obj.object_identity);
+    END LOOP;
+END
+$$;
+CREATE EVENT TRIGGER regress_event_trigger_drop_objects ON sql_drop
+	WHEN TAG IN ('drop table', 'drop function', 'drop view',
+		'drop owned', 'drop schema', 'alter table')
+	EXECUTE PROCEDURE test_evtrig_dropped_objects();
+ALTER TABLE schema_one.table_one DROP COLUMN a;
+DROP SCHEMA schema_one, schema_two CASCADE;
+NOTICE:  drop cascades to 7 other objects
+DETAIL:  drop cascades to table schema_two.table_two
+drop cascades to table schema_two.table_three
+drop cascades to function schema_two.add(integer,integer)
+drop cascades to function schema_two.newton(integer)
+drop cascades to table schema_one.table_one
+drop cascades to table schema_one."table two"
+drop cascades to table schema_one.table_three
+NOTICE:  table "schema_two_table_two" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_two_table_two"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "audit_tbls_schema_two_table_three" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.audit_tbls_schema_two_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_two_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+ERROR:  object audit_tbls.schema_two_table_three of type table cannot be dropped
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_two_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+DELETE FROM undroppable_objs WHERE object_identity = 'audit_tbls.schema_two_table_three';
+DROP SCHEMA schema_one, schema_two CASCADE;
+NOTICE:  drop cascades to 7 other objects
+DETAIL:  drop cascades to table schema_two.table_two
+drop cascades to table schema_two.table_three
+drop cascades to function schema_two.add(integer,integer)
+drop cascades to function schema_two.newton(integer)
+drop cascades to table schema_one.table_one
+drop cascades to table schema_one."table two"
+drop cascades to table schema_one.table_three
+NOTICE:  table "schema_two_table_two" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_two_table_two"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "audit_tbls_schema_two_table_three" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.audit_tbls_schema_two_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_two_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "schema_one_table_one" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_one_table_one"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "schema_one_table two" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls."schema_one_table two""
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "schema_one_table_three" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_one_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+ERROR:  object schema_one.table_three of type table cannot be dropped
+DELETE FROM undroppable_objs WHERE object_identity = 'schema_one.table_three';
+DROP SCHEMA schema_one, schema_two CASCADE;
+NOTICE:  drop cascades to 7 other objects
+DETAIL:  drop cascades to table schema_two.table_two
+drop cascades to table schema_two.table_three
+drop cascades to function schema_two.add(integer,integer)
+drop cascades to function schema_two.newton(integer)
+drop cascades to table schema_one.table_one
+drop cascades to table schema_one."table two"
+drop cascades to table schema_one.table_three
+NOTICE:  table "schema_two_table_two" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_two_table_two"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "audit_tbls_schema_two_table_three" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.audit_tbls_schema_two_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_two_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "schema_one_table_one" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_one_table_one"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "schema_one_table two" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls."schema_one_table two""
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+NOTICE:  table "schema_one_table_three" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.schema_one_table_three"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+SELECT * FROM dropped_objects WHERE schema IS NULL OR schema <> 'pg_toast';
+     type     |   schema   |               object                
+--------------+------------+-------------------------------------
+ table column | schema_one | schema_one.table_one.a
+ schema       |            | schema_two
+ table        | schema_two | schema_two.table_two
+ type         | schema_two | schema_two.table_two
+ type         | schema_two | schema_two.table_two[]
+ table        | audit_tbls | audit_tbls.schema_two_table_three
+ type         | audit_tbls | audit_tbls.schema_two_table_three
+ type         | audit_tbls | audit_tbls.schema_two_table_three[]
+ table        | schema_two | schema_two.table_three
+ type         | schema_two | schema_two.table_three
+ type         | schema_two | schema_two.table_three[]
+ function     | schema_two | schema_two.add(integer,integer)
+ aggregate    | schema_two | schema_two.newton(integer)
+ schema       |            | schema_one
+ table        | schema_one | schema_one.table_one
+ type         | schema_one | schema_one.table_one
+ type         | schema_one | schema_one.table_one[]
+ table        | schema_one | schema_one."table two"
+ type         | schema_one | schema_one."table two"
+ type         | schema_one | schema_one."table two"[]
+ table        | schema_one | schema_one.table_three
+ type         | schema_one | schema_one.table_three
+ type         | schema_one | schema_one.table_three[]
+(23 rows)
+
+DROP OWNED BY regression_bob;
+NOTICE:  table "audit_tbls_schema_one_table_two" does not exist, skipping
+CONTEXT:  SQL statement "DROP TABLE IF EXISTS audit_tbls.audit_tbls_schema_one_table_two"
+PL/pgSQL function test_evtrig_dropped_objects() line 8 at EXECUTE statement
+SELECT * FROM dropped_objects WHERE type = 'schema';
+  type  | schema |   object   
+--------+--------+------------
+ schema |        | schema_two
+ schema |        | schema_one
+ schema |        | audit_tbls
+(3 rows)
+
+DROP ROLE regression_bob;
+DROP EVENT TRIGGER regress_event_trigger_drop_objects;
+DROP EVENT TRIGGER undroppable;
diff --git a/src/test/regress/sql/event_trigger.sql b/src/test/regress/sql/event_trigger.sql
index a07dcd75546..11d2ce5c133 100644
--- a/src/test/regress/sql/event_trigger.sql
+++ b/src/test/regress/sql/event_trigger.sql
@@ -97,10 +97,112 @@ drop event trigger regress_event_trigger;
 -- should fail, regression_bob owns regress_event_trigger2/3
 drop role regression_bob;
 
+-- cleanup before next test
 -- these are all OK; the second one should emit a NOTICE
 drop event trigger if exists regress_event_trigger2;
 drop event trigger if exists regress_event_trigger2;
 drop event trigger regress_event_trigger3;
 drop event trigger regress_event_trigger_end;
-drop function test_event_trigger();
-drop role regression_bob;
+
+-- test support for dropped objects
+CREATE SCHEMA schema_one authorization regression_bob;
+CREATE SCHEMA schema_two authorization regression_bob;
+CREATE SCHEMA audit_tbls authorization regression_bob;
+SET SESSION AUTHORIZATION regression_bob;
+
+CREATE TABLE schema_one.table_one(a int);
+CREATE TABLE schema_one."table two"(a int);
+CREATE TABLE schema_one.table_three(a int);
+CREATE TABLE audit_tbls.schema_one_table_two(the_value text);
+
+CREATE TABLE schema_two.table_two(a int);
+CREATE TABLE schema_two.table_three(a int, b text);
+CREATE TABLE audit_tbls.schema_two_table_three(the_value text);
+
+CREATE OR REPLACE FUNCTION schema_two.add(int, int) RETURNS int LANGUAGE plpgsql
+  CALLED ON NULL INPUT
+  AS $$ BEGIN RETURN coalesce($1,0) + coalesce($2,0); END; $$;
+CREATE AGGREGATE schema_two.newton
+  (BASETYPE = int, SFUNC = schema_two.add, STYPE = int);
+
+RESET SESSION AUTHORIZATION;
+
+CREATE TABLE undroppable_objs (
+	object_type text,
+	object_identity text
+);
+INSERT INTO undroppable_objs VALUES
+('table', 'schema_one.table_three'),
+('table', 'audit_tbls.schema_two_table_three');
+
+CREATE TABLE dropped_objects (
+	type text,
+	schema text,
+	object text
+);
+
+-- This tests errors raised within event triggers; the one in audit_tbls
+-- uses 2nd-level recursive invocation via test_evtrig_dropped_objects().
+CREATE OR REPLACE FUNCTION undroppable() RETURNS event_trigger
+LANGUAGE plpgsql AS $$
+DECLARE
+	obj record;
+BEGIN
+	PERFORM 1 FROM pg_tables WHERE tablename = 'undroppable_objs';
+	IF NOT FOUND THEN
+		RAISE NOTICE 'table undroppable_objs not found, skipping';
+		RETURN;
+	END IF;
+	FOR obj IN
+		SELECT * FROM pg_event_trigger_dropped_objects() JOIN
+			undroppable_objs USING (object_type, object_identity)
+	LOOP
+		RAISE EXCEPTION 'object % of type % cannot be dropped',
+			obj.object_identity, obj.object_type;
+	END LOOP;
+END;
+$$;
+
+CREATE EVENT TRIGGER undroppable ON sql_drop
+	EXECUTE PROCEDURE undroppable();
+
+CREATE OR REPLACE FUNCTION test_evtrig_dropped_objects() RETURNS event_trigger
+LANGUAGE plpgsql AS $$
+DECLARE
+    obj record;
+BEGIN
+    FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
+    LOOP
+        IF obj.object_type = 'table' THEN
+                EXECUTE format('DROP TABLE IF EXISTS audit_tbls.%I',
+					format('%s_%s', obj.schema_name, obj.object_name));
+        END IF;
+
+	INSERT INTO dropped_objects
+		(type, schema, object) VALUES
+		(obj.object_type, obj.schema_name, obj.object_identity);
+    END LOOP;
+END
+$$;
+
+CREATE EVENT TRIGGER regress_event_trigger_drop_objects ON sql_drop
+	WHEN TAG IN ('drop table', 'drop function', 'drop view',
+		'drop owned', 'drop schema', 'alter table')
+	EXECUTE PROCEDURE test_evtrig_dropped_objects();
+
+ALTER TABLE schema_one.table_one DROP COLUMN a;
+DROP SCHEMA schema_one, schema_two CASCADE;
+DELETE FROM undroppable_objs WHERE object_identity = 'audit_tbls.schema_two_table_three';
+DROP SCHEMA schema_one, schema_two CASCADE;
+DELETE FROM undroppable_objs WHERE object_identity = 'schema_one.table_three';
+DROP SCHEMA schema_one, schema_two CASCADE;
+
+SELECT * FROM dropped_objects WHERE schema IS NULL OR schema <> 'pg_toast';
+
+DROP OWNED BY regression_bob;
+SELECT * FROM dropped_objects WHERE type = 'schema';
+
+DROP ROLE regression_bob;
+
+DROP EVENT TRIGGER regress_event_trigger_drop_objects;
+DROP EVENT TRIGGER undroppable;