fix: Fix the issue of actor migration panic caused by the in-place scale-down

src/meta/src/barrier/context/recovery.rs

@@ -427,13 +427,13 @@ impl GlobalBarrierWorkerContextImpl {
             .collect();
 
         if expired_worker_slots.is_empty() {
-            debug!("no expired worker slots, skipping.");
+            info!("no expired worker slots, skipping.");
             return self.resolve_graph_info(None).await;
         }
 
-        debug!("start migrate actors.");
+        info!("start migrate actors.");
         let mut to_migrate_worker_slots = expired_worker_slots.into_iter().rev().collect_vec();
-        debug!("got to migrate worker slots {:#?}", to_migrate_worker_slots);
+        info!("got to migrate worker slots {:#?}", to_migrate_worker_slots);
 
         let mut inuse_worker_slots: HashSet<_> = all_inuse_worker_slots
             .intersection(&active_worker_slots)
@@ -535,6 +535,8 @@ impl GlobalBarrierWorkerContextImpl {
             warn!(?changed, "get worker changed or timed out. Retry migrate");
         }
 
+        info!("migration plan {:?}", plan);
+
         mgr.catalog_controller.migrate_actors(plan).await?;
 
         info!("migrate actors succeed.");

src/meta/src/controller/fragment.rs

@@ -1125,12 +1125,17 @@ impl CatalogController {
                 .insert(*actor_id);
         }
 
-        let expired_workers: HashSet<_> = plan.keys().map(|k| k.worker_id() as WorkerId).collect();
+        let expired_or_changed_workers: HashSet<_> =
+            plan.keys().map(|k| k.worker_id() as WorkerId).collect();
 
         let mut actor_migration_plan = HashMap::new();
         for (worker, fragment) in actor_locations {
-            if expired_workers.contains(&worker) {
-                for (_, actors) in fragment {
+            if expired_or_changed_workers.contains(&worker) {
+                for (fragment_id, actors) in fragment {
+                    debug!(
+                        "worker {} expired or changed, migrating fragment {}",
+                        worker, fragment_id
+                    );
                     let worker_slot_to_actor: HashMap<_, _> = actors
                         .iter()
                         .enumerate()
@@ -1140,8 +1145,9 @@ impl CatalogController {
                         .collect();
 
                     for (worker_slot, actor) in worker_slot_to_actor {
-                        actor_migration_plan
-                            .insert(actor, plan[&worker_slot].worker_id() as WorkerId);
+                        if let Some(target) = plan.get(&worker_slot) {
+                            actor_migration_plan.insert(actor, target.worker_id() as WorkerId);
+                        }
                     }
                 }
             }