Updated due to comments

application/src/main/java/org/thingsboard/server/service/entitiy/alarm/DefaultTbAlarmService.java

@@ -39,6 +39,7 @@ import org.thingsboard.server.common.data.id.EntityId;
 import org.thingsboard.server.common.data.id.TenantId;
 import org.thingsboard.server.common.data.id.UserId;
 import org.thingsboard.server.dao.eventsourcing.DeleteEntityEvent;
+import org.thingsboard.server.dao.housekeeper.HouseKeeperService;
 import org.thingsboard.server.service.entitiy.AbstractTbEntityService;
 
 import java.util.List;
@@ -51,6 +52,9 @@ public class DefaultTbAlarmService extends AbstractTbEntityService implements Tb
     @Autowired
     protected TbAlarmCommentService alarmCommentService;
 
+    @Autowired
+    private HouseKeeperService housekeeper;
+
     @Override
     public Alarm save(Alarm alarm, User user) throws ThingsboardException {
         ActionType actionType = alarm.getId() == null ? ActionType.ADDED : ActionType.UPDATED;
@@ -220,16 +224,10 @@ public class DefaultTbAlarmService extends AbstractTbEntityService implements Tb
     }
 
     @Override
-    public Boolean delete(Alarm alarm, User user) {
-        TenantId tenantId = alarm.getTenantId();
-        notificationEntityService.logEntityAction(tenantId, alarm.getOriginator(), alarm, alarm.getCustomerId(),
-                ActionType.DELETED, user);
-        return alarmSubscriptionService.deleteAlarm(tenantId, alarm.getId());
-    }
-
-    private void unassignDeletedUserAlarms(User user) {
+    public List<AlarmId> unassignDeletedUserAlarms(User user) {
         List<AlarmId> alarmIds = alarmService.findAlarmIdsByAssigneeId(user.getId());
         for (AlarmId alarmId : alarmIds) {
+            log.trace("[{}] Unassigning alarm {} userId {}", user.getTenantId().getId(), alarmId.getId(), user.getId().getId());
             AlarmApiCallResult result = alarmSubscriptionService.unassignAlarm(user.getTenantId(), alarmId, System.currentTimeMillis());
             Alarm alarm = result.getAlarm();
             if (!result.isSuccessful()) {
@@ -254,21 +252,26 @@ public class DefaultTbAlarmService extends AbstractTbEntityService implements Tb
                         alarm.getCustomerId(), ActionType.ALARM_UNASSIGNED, null);
             }
         }
+        return alarmIds;
     }
 
     @TransactionalEventListener(fallbackExecution = true)
     public void handleEvent(DeleteEntityEvent<?> event) {
-        try {
-            log.trace("[{}] DeleteEntityEvent called: {}", event.getTenantId(), event);
-            EntityId entityId = event.getEntityId();
-            if (EntityType.USER.equals(entityId.getEntityType())) {
-                unassignDeletedUserAlarms((User) event.getEntity());
-            }
-        } catch (Exception e) {
-            log.error("[{}] failed to process DeleteEntityEvent: {}", event.getTenantId(), event);
+        log.trace("[{}] DeleteEntityEvent called: {}", event.getTenantId(), event);
+        EntityId entityId = event.getEntityId();
+        if (EntityType.USER.equals(entityId.getEntityType())) {
+            housekeeper.unassignDeletedUserAlarms((User) event.getEntity());
         }
     }
 
+    @Override
+    public Boolean delete(Alarm alarm, User user) {
+        TenantId tenantId = alarm.getTenantId();
+        notificationEntityService.logEntityAction(tenantId, alarm.getOriginator(), alarm, alarm.getCustomerId(),
+                ActionType.DELETED, user);
+        return alarmSubscriptionService.deleteAlarm(tenantId, alarm.getId());
+    }
+
     private static long getOrDefault(long ts) {
         return ts > 0 ? ts : System.currentTimeMillis();
     }

application/src/main/java/org/thingsboard/server/service/entitiy/alarm/TbAlarmService.java

@@ -19,8 +19,11 @@ import org.thingsboard.server.common.data.User;
 import org.thingsboard.server.common.data.alarm.Alarm;
 import org.thingsboard.server.common.data.alarm.AlarmInfo;
 import org.thingsboard.server.common.data.exception.ThingsboardException;
+import org.thingsboard.server.common.data.id.AlarmId;
 import org.thingsboard.server.common.data.id.UserId;
 
+import java.util.List;
+
 public interface TbAlarmService {
 
     Alarm save(Alarm entity, User user) throws ThingsboardException;
@@ -37,5 +40,7 @@ public interface TbAlarmService {
 
     AlarmInfo unassign(Alarm alarm, long unassignTs, User user) throws ThingsboardException;
 
+    List<AlarmId> unassignDeletedUserAlarms(User user);
+
     Boolean delete(Alarm alarm, User user);
 }

application/src/main/java/org/thingsboard/server/service/housekeeper/InMemoryHouseKeeperServiceService.java

@@ -0,0 +1,73 @@
+/**
+ * Copyright © 2016-2023 The Thingsboard Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.thingsboard.server.service.housekeeper;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.ListeningExecutorService;
+import com.google.common.util.concurrent.MoreExecutors;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.context.annotation.Lazy;
+import org.springframework.stereotype.Component;
+import org.thingsboard.common.util.ThingsBoardThreadFactory;
+import org.thingsboard.server.common.data.User;
+import org.thingsboard.server.common.data.id.AlarmId;
+import org.thingsboard.server.dao.housekeeper.HouseKeeperService;
+import org.thingsboard.server.service.entitiy.alarm.TbAlarmService;
+
+import javax.annotation.PostConstruct;
+import javax.annotation.PreDestroy;
+import java.util.List;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicInteger;
+
+@Component
+@RequiredArgsConstructor
+@Slf4j
+public class InMemoryHouseKeeperServiceService implements HouseKeeperService {
+
+    @Lazy
+    final TbAlarmService alarmService;
+
+    ListeningExecutorService executor;
+
+    AtomicInteger queueSize = new AtomicInteger();
+
+    @PostConstruct
+    public void init() {
+         executor = MoreExecutors.listeningDecorator(Executors.newSingleThreadExecutor(ThingsBoardThreadFactory.forName("housekeeper")));
+    }
+
+    @PreDestroy
+    public void destroy() {
+        if (executor != null) {
+            executor.shutdown();
+        }
+    }
+
+    @Override
+    public ListenableFuture<List<AlarmId>> unassignDeletedUserAlarms(User user) {
+        log.debug("[{}][{}] unassignDeletedUserAlarms submitting, pending queue size: {} ", user.getTenantId().getId(), user.getId().getId(), queueSize.get());
+        queueSize.incrementAndGet();
+        ListenableFuture<List<AlarmId>> future = executor.submit(() -> alarmService.unassignDeletedUserAlarms(user));
+        future.addListener(() -> {
+            queueSize.decrementAndGet();
+            log.debug("[{}][{}] unassignDeletedUserAlarms finished, pending queue size: {} ", user.getTenantId().getId(), user.getId().getId(), queueSize.get());
+        }, MoreExecutors.directExecutor());
+        return future;
+    }
+
+}

common/dao-api/src/main/java/org/thingsboard/server/dao/housekeeper/HouseKeeperService.java

@@ -0,0 +1,27 @@
+/**
+ * Copyright © 2016-2023 The Thingsboard Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.thingsboard.server.dao.housekeeper;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import org.thingsboard.server.common.data.User;
+import org.thingsboard.server.common.data.id.AlarmId;
+
+import java.util.List;
+
+public interface HouseKeeperService {
+    ListenableFuture<List<AlarmId>> unassignDeletedUserAlarms(User user);
+
+}

dao/src/main/java/org/thingsboard/server/dao/DaoUtil.java

@@ -33,6 +33,7 @@ import java.util.Optional;
 import java.util.UUID;
 import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.stream.Collectors;
 
 public abstract class DaoUtil {
 
@@ -109,6 +110,10 @@ public abstract class DaoUtil {
         return ids;
     }
 
+    public static <I> List<I> fromUUIDs(List<UUID> uuids, Function<UUID, I> mapper) {
+        return uuids.stream().map(mapper).collect(Collectors.toList());
+    }
+
     public static <I> I toEntityId(UUID uuid, Function<UUID, I> creator) {
         if (uuid != null) {
             return creator.apply(uuid);

dao/src/main/java/org/thingsboard/server/dao/sql/alarm/JpaAlarmDao.java

@@ -289,7 +289,7 @@ public class JpaAlarmDao extends JpaAbstractDao<AlarmEntity, Alarm> implements A
     @Override
     public List<AlarmId> findAlarmIdsByAssigneeId(UUID key) {
         List<UUID> assignedAlarmIds = alarmRepository.findAlarmIdsByAssigneeId(key);
-        return assignedAlarmIds.stream().map(AlarmId::new).collect(Collectors.toList());
+        return DaoUtil.fromUUIDs(assignedAlarmIds, AlarmId::new);
     }
 
     @Override