Remove logic for converting a table to a view.

Up to now we have allowed manual creation of an ON SELECT rule on
a table to convert it into a view.  That was never anything but a
horrid, error-prone hack though.  pg_dump used to rely on that
behavior to deal with cases involving circular dependencies,
where a dependency loop could be broken by separating the creation
of a view from installation of its ON SELECT rule.  However, we
changed pg_dump to use CREATE OR REPLACE VIEW for that in commit
d8c05aff5 (which was later back-patched as far as 9.4), so there's
not a good argument anymore for continuing to support the behavior.

The proximate reason for axing it now is that we found that the
new statistics code has failure modes associated with the relkind
change caused by this behavior.  We'll patch around that in v15,
but going forward it seems like a better idea to get rid of the
need to support relkind changes.

Discussion: https://postgr.es/m/CALDaNm2yXz+zOtv7y5zBd5WKT8O0Ld3YxikuU3dcyCvxF7gypA@mail.gmail.com

1 files changed, 12 insertions, 177 deletions

diff --git a/src/backend/rewrite/rewriteDefine.c b/src/backend/rewrite/rewriteDefine.c
index db45d8a08b2..8ac2c81b06b 100644
--- a/src/backend/rewrite/rewriteDefine.c
+++ b/src/backend/rewrite/rewriteDefine.c
@@ -239,7 +239,6 @@ DefineQueryRewrite(const char *rulename,
 	Relation	event_relation;
 	ListCell   *l;
 	Query	   *query;
-	bool		RelisBecomingView = false;
 	Oid			ruleId = InvalidOid;
 	ObjectAddress address;
 
@@ -311,7 +310,18 @@ DefineQueryRewrite(const char *rulename,
 		/*
 		 * Rules ON SELECT are restricted to view definitions
 		 *
-		 * So there cannot be INSTEAD NOTHING, ...
+		 * So this had better be a view, ...
+		 */
+		if (event_relation->rd_rel->relkind != RELKIND_VIEW &&
+			event_relation->rd_rel->relkind != RELKIND_MATVIEW)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("relation \"%s\" cannot have ON SELECT rules",
+							RelationGetRelationName(event_relation)),
+					 errdetail_relkind_not_supported(event_relation->rd_rel->relkind)));
+
+		/*
+		 * ... there cannot be INSTEAD NOTHING, ...
 		 */
 		if (action == NIL)
 			ereport(ERROR,
@@ -407,93 +417,6 @@ DefineQueryRewrite(const char *rulename,
 								ViewSelectRuleName)));
 			rulename = pstrdup(ViewSelectRuleName);
 		}
-
-		/*
-		 * Are we converting a relation to a view?
-		 *
-		 * If so, check that the relation is empty because the storage for the
-		 * relation is going to be deleted.  Also insist that the rel not be
-		 * involved in partitioning, nor have any triggers, indexes, child or
-		 * parent tables, RLS policies, or RLS enabled.  (Note: some of these
-		 * tests are too strict, because they will reject relations that once
-		 * had such but don't anymore.  But we don't really care, because this
-		 * whole business of converting relations to views is just an obsolete
-		 * kluge to allow dump/reload of views that participate in circular
-		 * dependencies.)
-		 */
-		if (event_relation->rd_rel->relkind != RELKIND_VIEW &&
-			event_relation->rd_rel->relkind != RELKIND_MATVIEW)
-		{
-			TableScanDesc scanDesc;
-			Snapshot	snapshot;
-			TupleTableSlot *slot;
-
-			if (event_relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
-				ereport(ERROR,
-						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("cannot convert partitioned table \"%s\" to a view",
-								RelationGetRelationName(event_relation))));
-
-			/* only case left: */
-			Assert(event_relation->rd_rel->relkind == RELKIND_RELATION);
-
-			if (event_relation->rd_rel->relispartition)
-				ereport(ERROR,
-						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("cannot convert partition \"%s\" to a view",
-								RelationGetRelationName(event_relation))));
-
-			snapshot = RegisterSnapshot(GetLatestSnapshot());
-			scanDesc = table_beginscan(event_relation, snapshot, 0, NULL);
-			slot = table_slot_create(event_relation, NULL);
-			if (table_scan_getnextslot(scanDesc, ForwardScanDirection, slot))
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-						 errmsg("could not convert table \"%s\" to a view because it is not empty",
-								RelationGetRelationName(event_relation))));
-			ExecDropSingleTupleTableSlot(slot);
-			table_endscan(scanDesc);
-			UnregisterSnapshot(snapshot);
-
-			if (event_relation->rd_rel->relhastriggers)
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-						 errmsg("could not convert table \"%s\" to a view because it has triggers",
-								RelationGetRelationName(event_relation)),
-						 errhint("In particular, the table cannot be involved in any foreign key relationships.")));
-
-			if (event_relation->rd_rel->relhasindex)
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-						 errmsg("could not convert table \"%s\" to a view because it has indexes",
-								RelationGetRelationName(event_relation))));
-
-			if (event_relation->rd_rel->relhassubclass)
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-						 errmsg("could not convert table \"%s\" to a view because it has child tables",
-								RelationGetRelationName(event_relation))));
-
-			if (has_superclass(RelationGetRelid(event_relation)))
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-						 errmsg("could not convert table \"%s\" to a view because it has parent tables",
-								RelationGetRelationName(event_relation))));
-
-			if (event_relation->rd_rel->relrowsecurity)
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-						 errmsg("could not convert table \"%s\" to a view because it has row security enabled",
-								RelationGetRelationName(event_relation))));
-
-			if (relation_has_policies(event_relation))
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-						 errmsg("could not convert table \"%s\" to a view because it has row security policies",
-								RelationGetRelationName(event_relation))));
-
-			RelisBecomingView = true;
-		}
 	}
 	else
 	{
@@ -569,94 +492,6 @@ DefineQueryRewrite(const char *rulename,
 		SetRelationRuleStatus(event_relid, true);
 	}
 
-	/* ---------------------------------------------------------------------
-	 * If the relation is becoming a view:
-	 * - delete the associated storage files
-	 * - get rid of any system attributes in pg_attribute; a view shouldn't
-	 *	 have any of those
-	 * - remove the toast table; there is no need for it anymore, and its
-	 *	 presence would make vacuum slightly more complicated
-	 * - set relkind to RELKIND_VIEW, and adjust other pg_class fields
-	 *	 to be appropriate for a view
-	 *
-	 * NB: we had better have AccessExclusiveLock to do this ...
-	 * ---------------------------------------------------------------------
-	 */
-	if (RelisBecomingView)
-	{
-		Relation	relationRelation;
-		Oid			toastrelid;
-		HeapTuple	classTup;
-		Form_pg_class classForm;
-
-		relationRelation = table_open(RelationRelationId, RowExclusiveLock);
-		toastrelid = event_relation->rd_rel->reltoastrelid;
-
-		/* drop storage while table still looks like a table  */
-		RelationDropStorage(event_relation);
-		DeleteSystemAttributeTuples(event_relid);
-
-		/*
-		 * Drop the toast table if any.  (This won't take care of updating the
-		 * toast fields in the relation's own pg_class entry; we handle that
-		 * below.)
-		 */
-		if (OidIsValid(toastrelid))
-		{
-			ObjectAddress toastobject;
-
-			/*
-			 * Delete the dependency of the toast relation on the main
-			 * relation so we can drop the former without dropping the latter.
-			 */
-			deleteDependencyRecordsFor(RelationRelationId, toastrelid,
-									   false);
-
-			/* Make deletion of dependency record visible */
-			CommandCounterIncrement();
-
-			/* Now drop toast table, including its index */
-			toastobject.classId = RelationRelationId;
-			toastobject.objectId = toastrelid;
-			toastobject.objectSubId = 0;
-			performDeletion(&toastobject, DROP_RESTRICT,
-							PERFORM_DELETION_INTERNAL);
-		}
-
-		/*
-		 * SetRelationRuleStatus may have updated the pg_class row, so we must
-		 * advance the command counter before trying to update it again.
-		 */
-		CommandCounterIncrement();
-
-		/*
-		 * Fix pg_class entry to look like a normal view's, including setting
-		 * the correct relkind and removal of reltoastrelid of the toast table
-		 * we potentially removed above.
-		 */
-		classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(event_relid));
-		if (!HeapTupleIsValid(classTup))
-			elog(ERROR, "cache lookup failed for relation %u", event_relid);
-		classForm = (Form_pg_class) GETSTRUCT(classTup);
-
-		classForm->relam = InvalidOid;
-		classForm->reltablespace = InvalidOid;
-		classForm->relpages = 0;
-		classForm->reltuples = -1;
-		classForm->relallvisible = 0;
-		classForm->reltoastrelid = InvalidOid;
-		classForm->relhasindex = false;
-		classForm->relkind = RELKIND_VIEW;
-		classForm->relfrozenxid = InvalidTransactionId;
-		classForm->relminmxid = InvalidMultiXactId;
-		classForm->relreplident = REPLICA_IDENTITY_NOTHING;
-
-		CatalogTupleUpdate(relationRelation, &classTup->t_self, classTup);
-
-		heap_freetuple(classTup);
-		table_close(relationRelation, RowExclusiveLock);
-	}
-
 	ObjectAddressSet(address, RewriteRelationId, ruleId);
 
 	/* Close rel, but keep lock till commit... */