diff --git a/optimizer_worker.py b/optimizer_worker.py
index 050326a..d8970fe 100644
--- a/optimizer_worker.py
+++ b/optimizer_worker.py
@@ -41,13 +41,14 @@ def rabbit_callback(ch, method, properties, body):
             "task_id": task.task_id
         }
     send_reply(ch, json.dumps(res).encode("utf-8"))
+    ch.basic_ack(delivery_tag=method.delivery_tag)
 
 
 def main():
     channel = get_channel()
 
     channel.basic_consume(
-        queue=RABBIT_TASK_QUEUE, on_message_callback=rabbit_callback, auto_ack=True
+        queue=RABBIT_TASK_QUEUE, on_message_callback=rabbit_callback, auto_ack=False
     )
     channel.start_consuming()
 
diff --git a/src/rabbit.py b/src/rabbit.py
index b3d8e68..84fac4c 100644
--- a/src/rabbit.py
+++ b/src/rabbit.py
@@ -55,7 +55,7 @@ def get_channel(connection: Optional[BlockingConnection] = None) -> Channel:
     channel.queue_declare(queue=RABBIT_REPLY_QUEUE, **base_queue_params)
     channel.queue_declare(queue=RABBIT_TASK_QUEUE, **base_queue_params)
 
-    channel.basic_qos(prefetch_count=1)
+    channel.basic_qos(prefetch_count=4)
     return channel
 
 
@@ -64,7 +64,11 @@ def send_task(channel: Channel, data: bytes):
         exchange="",
         routing_key=RABBIT_TASK_QUEUE,
         body=data,
-        properties=BasicProperties(expiration=RABBIT_MESSAGE_TTL, reply_to=RABBIT_REPLY_QUEUE),
+        properties=BasicProperties(
+            expiration=RABBIT_MESSAGE_TTL,
+            reply_to=RABBIT_REPLY_QUEUE,
+            delivery_mode=2,  # make message persistent
+        ),
     )
 
 
@@ -73,7 +77,10 @@ def send_reply(channel, data: bytes):
         exchange="",
         routing_key=RABBIT_REPLY_QUEUE,
         body=data,
-        properties=BasicProperties(expiration=RABBIT_MESSAGE_TTL),
+        properties=BasicProperties(
+            expiration=RABBIT_MESSAGE_TTL,
+            # delivery_mode=2,  # make message persistent
+        ),
     )