Prioritize older instances and tasks

backend/postgres/postgres.go

@@ -778,7 +778,9 @@ func (be *postgresBackend) GetOrchestrationWorkItem(ctx context.Context) (*backe
 				SELECT 1 FROM NewEvents E
 				WHERE E.InstanceID = I.InstanceID AND (E.VisibleTime IS NULL OR E.VisibleTime < $4)
 			)
+			ORDER BY I.SequenceNumber ASC
 			LIMIT 1
+			FOR UPDATE SKIP LOCKED
 		) RETURNING InstanceID`,
 		be.workerName,     // LockedBy for Instances table
 		newLockExpiration, // Updated LockExpiration for Instances table
@@ -864,7 +866,9 @@ func (be *postgresBackend) GetActivityWorkItem(ctx context.Context) (*backend.Ac
 		WHERE SequenceNumber = (
 			SELECT SequenceNumber FROM NewTasks T
 			WHERE T.LockExpiration IS NULL OR T.LockExpiration < $3
+			ORDER BY T.SequenceNumber ASC
 			LIMIT 1
+			FOR UPDATE SKIP LOCKED
 		) RETURNING SequenceNumber, InstanceID, EventPayload`,
 		be.workerName,
 		newLockExpiration,

backend/postgres/schema.sql

@@ -18,6 +18,9 @@ CREATE TABLE IF NOT EXISTS Instances (
     ParentInstanceID TEXT NULL
 );
 
+-- This index is used to improve queries with ORDER BY Instances.SequenceNumber
+CREATE INDEX IF NOT EXISTS IX_Instances_SequenceNumber ON Instances(SequenceNumber);
+
 -- This index is used by LockNext and Purge logic
 CREATE INDEX IF NOT EXISTS IX_Instances_RuntimeStatus ON Instances(RuntimeStatus);
 

backend/sqlite/sqlite.go

@@ -852,6 +852,7 @@ func (be *sqliteBackend) GetActivityWorkItem(ctx context.Context) (*backend.Acti
 		WHERE [SequenceNumber] = (
 			SELECT [SequenceNumber] FROM NewTasks T
 			WHERE T.[LockExpiration] IS NULL OR T.[LockExpiration] < ?
+			ORDER BY T.[SequenceNumber] ASC
 			LIMIT 1
 		) RETURNING [SequenceNumber], [InstanceID], [EventPayload]`,
 		be.workerName,