Error "unknown delivery tag" occurs when i try ack messages to RabbitMQ using pika (python)

Question

I want process messages in few threads but i'm getting error during execute this code:

from __future__ import with_statement
import pika
import sys
from pika.adapters.blocking_connection import BlockingConnection
from pika import connection, credentials
import time
import threading
import random
from pika.adapters.select_connection import SelectConnection
from pika.connection import Connection
import traceback


def doWork(body, args, channel):


    r = random.random()
    time.sleep(r * 10)
    try:        
        channel.basic_ack(delivery_tag=args.delivery_tag)

    except :
        traceback.print_exc()


auth = credentials.PlainCredentials(username="guest", password="guest")
params = connection.ConnectionParameters(host="localhost", credentials=auth)
conn = BlockingConnection(params)
channel = conn.channel()


while True:

    time.sleep(0.03)    
    try:

        method_frame, header_frame, body = channel.basic_get(queue="test_queue")
        if method_frame.NAME == 'Basic.GetEmpty':
            continue        

        t = threading.Thread(target=doWork, args=[body, method_frame, channel])
        t.setDaemon(True)
        t.start()

    except Exception, e:
        traceback.print_exc()
        continue

Error desctiption:

Traceback (most recent call last):
  File "C:\work\projects\mq\start.py", line 43, in 
    method_frame, header_frame, body = channel.basic_get(queue="test_queue")
  File "C:\work\projects\mq\libs\pika\adapters\blocking_connection.py", line 318, in basic_get
    self.basic_get_(self, self._on_basic_get, ticket, queue, no_ack)
  File "C:\work\projects\mq\libs\pika\channel.py", line 469, in basic_get
    no_ack=no_ack))
  File "C:\work\projects\mq\libs\pika\adapters\blocking_connection.py", line 244, in send_method
    self.connection.process_data_events()
  File "C:\work\projects\mq\libs\pika\adapters\blocking_connection.py", line 94, in process_data_events
    self._handle_read()
  File "C:\work\projects\mq\libs\pika\adapters\base_connection.py", line 162, in _handle_read
    self._on_data_available(data)
  File "C:\work\projects\mq\libs\pika\connection.py", line 589, in _on_data_available
    frame)                 # Args
  File "C:\work\projects\mq\libs\pika\callback.py", line 124, in process
    callback(*args, **keywords)
  File "C:\work\projects\mq\libs\pika\adapters\blocking_connection.py", line 269, in _on_remote_close
    frame.method.reply_text)
AMQPChannelError: (406, 'PRECONDITION_FAILED - unknown delivery tag 204')

Versions: pika 0.9.5, rabbitMQ 2.6.1

Answer 1

The problem probably is that you're setting no_ack=True like this:

consumer_tag = channel.basic_consume(
    message_delivery_event,
    no_ack=True,
    queue=queue,
)

And then acknowledging the messages:

channel.basic_ack(delivery_tag=args.delivery_tag)

You have to chose if you want to acknowledge or not and set the correct consume parameter.