Speed up SequenceUsedInDistributedTable

This builds on the work to speed up EnsureSequenceTypeSupported, and now
does something similar for SequenceUsedInDistributedTable.
SequenceUsedInDistributedTable had a similar O(number of citus tables)
operation. This fixes that and speeds up creation of distributed tables
significantly when many distributed tables already exist.

src/backend/distributed/commands/sequence.c

@@ -14,6 +14,7 @@
 #include "access/xact.h"
 #include "catalog/dependency.h"
 #include "catalog/namespace.h"
+#include "catalog/pg_attrdef.h"
 #include "commands/defrem.h"
 #include "commands/extension.h"
 #include "nodes/makefuncs.h"
@@ -507,22 +508,14 @@ PreprocessAlterSequenceStmt(Node *node, const char *queryString,
 static Oid
 SequenceUsedInDistributedTable(const ObjectAddress *sequenceAddress, char depType)
 {
-	List *citusTableIdList = CitusTableTypeIdList(ANY_CITUS_TABLE_TYPE);
-	Oid citusTableId = InvalidOid;
-	foreach_oid(citusTableId, citusTableIdList)
+	Oid relationId;
+	List *relations = GetDependentRelationsWithSequence(sequenceAddress->objectId,
+														depType);
+	foreach_oid(relationId, relations)
 	{
-		List *seqInfoList = NIL;
-		GetDependentSequencesWithRelation(citusTableId, &seqInfoList, 0, depType);
-		SequenceInfo *seqInfo = NULL;
-		foreach_ptr(seqInfo, seqInfoList)
+		if (IsCitusTable(relationId))
 		{
-			/*
-			 * This sequence is used in a distributed table
-			 */
-			if (seqInfo->sequenceOid == sequenceAddress->objectId)
-			{
-				return citusTableId;
-			}
+			return relationId;
 		}
 	}
 

src/backend/distributed/metadata/metadata_sync.c

@@ -1637,6 +1637,74 @@ GetDependentSequencesWithRelation(Oid relationId, List **seqInfoList,
 }
 
 
+/*
+ * GetDependentDependentRelationsWithSequence returns a list of oids of
+ * relations that have have a dependency on the given sequence.
+ * There are three types of dependencies:
+ * 1. direct auto (owned sequences), created using SERIAL or BIGSERIAL
+ * 2. indirect auto (through an AttrDef), created using DEFAULT nextval('..')
+ * 3. internal, created using GENERATED ALWAYS AS IDENTITY
+ *
+ * Depending on the passed deptype, we return the relations that have the
+ * given type(s):
+ * - DEPENDENCY_AUTO returns both 1 and 2
+ * - DEPENDENCY_INTERNAL returns 3
+ *
+ * The returned list can contain duplicates, as the same relation can have
+ * multiple dependencies on the sequence.
+ */
+List *
+GetDependentRelationsWithSequence(Oid sequenceOid, char depType)
+{
+	List *relations = NIL;
+	ScanKeyData key[2];
+	HeapTuple tup;
+
+	Relation depRel = table_open(DependRelationId, AccessShareLock);
+
+	ScanKeyInit(&key[0],
+				Anum_pg_depend_classid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationRelationId));
+	ScanKeyInit(&key[1],
+				Anum_pg_depend_objid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(sequenceOid));
+	SysScanDesc scan = systable_beginscan(depRel, DependDependerIndexId, true,
+										  NULL, lengthof(key), key);
+	while (HeapTupleIsValid(tup = systable_getnext(scan)))
+	{
+		Form_pg_depend deprec = (Form_pg_depend) GETSTRUCT(tup);
+
+		if (
+			deprec->refclassid == RelationRelationId &&
+			deprec->refobjsubid != 0 &&
+			deprec->deptype == depType)
+		{
+			relations = lappend_oid(relations, deprec->refobjid);
+		}
+	}
+
+	systable_endscan(scan);
+
+	table_close(depRel, AccessShareLock);
+
+	if (depType == DEPENDENCY_AUTO)
+	{
+		Oid attrDefOid;
+		List *attrDefOids = GetAttrDefsFromSequence(sequenceOid);
+
+		foreach_oid(attrDefOid, attrDefOids)
+		{
+			ObjectAddress columnAddress = GetAttrDefaultColumnAddress(attrDefOid);
+			relations = lappend_oid(relations, columnAddress.objectId);
+		}
+	}
+
+	return relations;
+}
+
+
 /*
  * GetSequencesFromAttrDef returns a list of sequence OIDs that have
  * dependency with the given attrdefOid in pg_depend

src/include/distributed/metadata_sync.h

@@ -136,6 +136,7 @@ ObjectAddress GetAttrDefaultColumnAddress(Oid attrdefoid);
 extern List * GetAttrDefsFromSequence(Oid seqOid);
 extern void GetDependentSequencesWithRelation(Oid relationId, List **seqInfoList,
 											  AttrNumber attnum, char depType);
+extern List * GetDependentRelationsWithSequence(Oid seqId, char depType);
 extern List * GetDependentFunctionsWithRelation(Oid relationId);
 extern Oid GetAttributeTypeOid(Oid relationId, AttrNumber attnum);
 extern void SetLocalEnableMetadataSync(bool state);