芹菜任务中每个查询的Python cassandra-driver OperationTimeOut

Question

我对在 celery 任务中异步执行的每个插入查询（小查询）都有问题。 在同步模式下，当我确实插入时一切都做得很好，但是当它在 apply_async() 中执行时，我得到了这个：

OperationTimedOut('errors=errors=errors={}, last_host=***.***.*.***, last_host=None, last_host=None',)

追溯：

Traceback (most recent call last):
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/celery/app/trace.py", line 240, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/celery/app/trace.py", line 437, in __protected_call__
    return self.run(*args, **kwargs)
  File "/var/nfs_www/***/www_v1/app/mods/news_feed/tasks.py", line 26, in send_new_comment_reply_notifications
    send_new_comment_reply_notifications_method(comment_id)
  File "/var/nfs_www/***www_v1/app/mods/news_feed/methods.py", line 83, in send_new_comment_reply_notifications
    comment_type='comment_reply'
  File "/var/nfs_www/***/www_v1/app/mods/news_feed/models/storage.py", line 129, in add
    CommentsFeed(**kwargs).save()
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/cqlengine/models.py", line 531, in save
    consistency=self.__consistency__).save()
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/cqlengine/query.py", line 907, in save
    self._execute(insert)
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/cqlengine/query.py", line 786, in _execute
    tmp = execute(q, consistency_level=self._consistency)
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/cqlengine/connection.py", line 95, in execute
    result = session.execute(query, params)
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/cassandra/cluster.py", line 1103, in execute
    result = future.result(timeout)
  File "/var/nfs_www/***/env_v0/local/lib/python2.7/site-packages/cassandra/cluster.py", line 2475, in result
    raise OperationTimedOut(errors=self._errors, last_host=self._current_host)
OperationTimedOut: errors={}, last_host=***.***.*.***

有人对问题有想法吗？

我找到了这个When cassandra-driver was executing the query, cassandra-driver returned error OperationTimedOut，但我的查询很少，而且只在 celery 任务中出现问题。

更新：

我做了一个测试任务，它也引发了这个错误。

@celery.task()
def test_task_with_cassandra():
    from app import cassandra_session
    cassandra_session.execute('use news_feed')
    return 'Done'

更新 2： 做了这个：

@celery.task()
def test_task_with_cassandra():
    from cqlengine import connection
    connection.setup(app.config['CASSANDRA_SERVERS'], port=app.config['CASSANDRA_PORT'],
                     default_keyspace='test_keyspace')
    from .models import Feed
    Feed.objects.count()
    return 'Done'

知道了：

NoHostAvailable('Unable to connect to any servers', {'***.***.*.***': OperationTimedOut('errors=errors=Timed out creating connection, last_host=None, last_host=None',)})

我可以从 shell 连接到它

更新 3： 从 github 问题上的已删除线程（在我的电子邮件中找到）：（这对我也有用） 以下是我将 CQLengine 插入 Celery 的方法：

from celery import Celery
from celery.signals import worker_process_init, beat_init
from cqlengine import connection
from cqlengine.connection import (
    cluster as cql_cluster, session as cql_session)

def cassandra_init():
    """ Initialize a clean Cassandra connection. """
    if cql_cluster is not None:
        cql_cluster.shutdown()
    if cql_session is not None:
        cql_session.shutdown()
    connection.setup()

# Initialize worker context for both standard and periodic tasks.
worker_process_init.connect(cassandra_init)
beat_init.connect(cassandra_init)

app = Celery()

这是粗略的，但有效。我们应该在 FAQ 中添加这个 sn-p 吗？

Answer 1

受 Ron 回答的启发，我想出了以下代码放入 tasks.py：

import threading
from django.conf import settings
from cassandra.cluster import Cluster
from celery.signals import worker_process_init,worker_process_shutdown

thread_local = threading.local()

@worker_process_init.connect
def open_cassandra_session(*args, **kwargs):
    cluster = Cluster([settings.DATABASES["cassandra"]["HOST"],], protocol_version=3)
    session = cluster.connect(settings.DATABASES["cassandra"]["NAME"])
    thread_local.cassandra_session = session

@worker_process_shutdown.connect
def close_cassandra_session(*args,**kwargs):
    session = thread_local.cassandra_session
    session.shutdown()
    thread_local.cassandra_session = None

这个简洁的解决方案将在 celery 工作进程启动和停止时自动打开/关闭 cassandra 会话。

旁注：protocol_version=3，因为 Cassandra 2.1 仅支持协议版本 3 及更低版本。

Answer 2

我遇到了类似的问题。它似乎与在任务之间共享 Cassandra 会话有关。我通过为每个线程创建一个会话来解决它。确保从您的任务中调用get_session()，然后执行以下操作：

thread_local = threading.local()

def get_session():
    if hasattr(thread_local, "cassandra_session"):
        return thread_local.cassandra_session

    cluster = Cluster(settings.CASSANDRA_HOSTS)
    session = cluster.connect(settings.CASSANDRA_KEYSPACE)

    thread_local.cassandra_session = session

    return session

Answer 3

其他答案对我不起作用，但问题的“更新 3”对我有用。这是我最终得到的结果（问题中建议的小更新）：

from celery.signals import worker_process_init
from cassandra.cqlengine import connection
from cassandra.cqlengine.connection import (
    cluster as cql_cluster, session as cql_session)

def cassandra_init(*args, **kwargs):
    """ Initialize a clean Cassandra connection. """
    if cql_cluster is not None:
        cql_cluster.shutdown()
    if cql_session is not None:
        cql_session.shutdown()
    connection.setup(settings.DATABASES["cassandra"]["HOST"].split(','), settings.DATABASES["cassandra"]["NAME"])

# Initialize worker context (only standard tasks)
worker_process_init.connect(cassandra_init)

Answer 4

使用 django-cassandra-engine 以下解决了我的问题：

db_connection = connections['cassandra']

@worker_process_init.connect
def connect_db(**_):
    db_connection.reconnect()


@worker_shutdown.connect
def disconnect(**_):
    db_connection.connection.close_all()

看here