Transfers: re-introduce last_processed_by logic in poller. Closes #6376

The protection provided by older_than, mentioned in
33f9578,
was over-estimated.

lib/rucio/core/request.py

@@ -688,7 +688,7 @@ def get_and_mark_next(
     for share in activity_shares:
 
         query = select(
-            models.Request
+            models.Request.id
         ).where(
             models.Request.state.in_(state),
             models.Request.request_type.in_(request_type)
@@ -744,6 +744,21 @@ def get_and_mark_next(
         else:
             query = query.limit(limit)
 
+        if session.bind.dialect.name == 'oracle':
+            query = select(
+                models.Request
+            ).where(
+                models.Request.id.in_(query)
+            ).with_for_update(
+                skip_locked=True
+            )
+        else:
+            query = query.with_only_columns(
+                models.Request
+            ).with_for_update(
+                skip_locked=True,
+                of=models.Request.last_processed_by
+            )
         query_result = session.execute(query).scalars()
         if query_result:
             if mode_all:

lib/rucio/daemons/conveyor/poller.py

@@ -66,6 +66,7 @@ def _fetch_requests(
         filter_transfertool,
         cached_topology,
         activity,
+        set_last_processed_by: bool,
         heartbeat_handler
 ):
     worker_number, total_workers, logger = heartbeat_handler.live()
@@ -77,6 +78,7 @@ def _fetch_requests(
         rse_collection=topology,
         request_type=[RequestType.TRANSFER, RequestType.STAGEIN, RequestType.STAGEOUT],
         state=[RequestState.SUBMITTED],
+        processed_by=heartbeat_handler.short_executable if set_last_processed_by else None,
         limit=db_bulk,
         older_than=datetime.datetime.utcnow() - datetime.timedelta(seconds=older_than) if older_than else None,
         total_workers=total_workers,
@@ -197,6 +199,7 @@ def _db_producer(*, activity: str, heartbeat_handler: "HeartbeatHandler"):
             filter_transfertool=filter_transfertool,
             cached_topology=cached_topology,
             activity=activity,
+            set_last_processed_by=not once,
             heartbeat_handler=heartbeat_handler,
         )