"""Apache Cassandra result store backend using the DataStax driver."""
import threading
from celery import states
from celery.exceptions import ImproperlyConfigured
from celery.utils.log import get_logger
from .base import BaseBackend
try: # pragma: no cover
import cassandra
import cassandra.auth
import cassandra.cluster
import cassandra.query
except ImportError:
cassandra = None
__all__ = ('CassandraBackend',)
logger = get_logger(__name__)
E_NO_CASSANDRA = """
You need to install the cassandra-driver library to
use the Cassandra backend. See https://github.com/datastax/python-driver
"""
E_NO_SUCH_CASSANDRA_AUTH_PROVIDER = """
CASSANDRA_AUTH_PROVIDER you provided is not a valid auth_provider class.
See https://datastax.github.io/python-driver/api/cassandra/auth.html.
"""
E_CASSANDRA_MISCONFIGURED = 'Cassandra backend improperly configured.'
E_CASSANDRA_NOT_CONFIGURED = 'Cassandra backend not configured.'
Q_INSERT_RESULT = """
INSERT INTO {table} (
task_id, status, result, date_done, traceback, children) VALUES (
%s, %s, %s, %s, %s, %s) {expires};
"""
Q_SELECT_RESULT = """
SELECT status, result, date_done, traceback, children
FROM {table}
WHERE task_id=%s
LIMIT 1
"""
Q_CREATE_RESULT_TABLE = """
CREATE TABLE {table} (
task_id text,
status text,
result blob,
date_done timestamp,
traceback blob,
children blob,
PRIMARY KEY ((task_id), date_done)
) WITH CLUSTERING ORDER BY (date_done DESC);
"""
Q_EXPIRES = """
USING TTL {0}
"""
def buf_t(x):
return bytes(x, 'utf8')
[документация]class CassandraBackend(BaseBackend):
"""Cassandra/AstraDB backend utilizing DataStax driver.
Raises:
celery.exceptions.ImproperlyConfigured:
if module :pypi:`cassandra-driver` is not available,
or not-exactly-one of the :setting:`cassandra_servers` and
the :setting:`cassandra_secure_bundle_path` settings is set.
"""
#: List of Cassandra servers with format: ``hostname``.
servers = None
#: Location of the secure connect bundle zipfile (absolute path).
bundle_path = None
supports_autoexpire = True # autoexpire supported via entry_ttl
def __init__(self, servers=None, keyspace=None, table=None, entry_ttl=None,
port=9042, bundle_path=None, **kwargs):
super().__init__(**kwargs)
if not cassandra:
raise ImproperlyConfigured(E_NO_CASSANDRA)
conf = self.app.conf
self.servers = servers or conf.get('cassandra_servers', None)
self.bundle_path = bundle_path or conf.get(
'cassandra_secure_bundle_path', None)
self.port = port or conf.get('cassandra_port', None)
self.keyspace = keyspace or conf.get('cassandra_keyspace', None)
self.table = table or conf.get('cassandra_table', None)
self.cassandra_options = conf.get('cassandra_options', {})
# either servers or bundle path must be provided...
db_directions = self.servers or self.bundle_path
if not db_directions or not self.keyspace or not self.table:
raise ImproperlyConfigured(E_CASSANDRA_NOT_CONFIGURED)
# ...but not both:
if self.servers and self.bundle_path:
raise ImproperlyConfigured(E_CASSANDRA_MISCONFIGURED)
expires = entry_ttl or conf.get('cassandra_entry_ttl', None)
self.cqlexpires = (
Q_EXPIRES.format(expires) if expires is not None else '')
read_cons = conf.get('cassandra_read_consistency') or 'LOCAL_QUORUM'
write_cons = conf.get('cassandra_write_consistency') or 'LOCAL_QUORUM'
self.read_consistency = getattr(
cassandra.ConsistencyLevel, read_cons,
cassandra.ConsistencyLevel.LOCAL_QUORUM)
self.write_consistency = getattr(
cassandra.ConsistencyLevel, write_cons,
cassandra.ConsistencyLevel.LOCAL_QUORUM)
self.auth_provider = None
auth_provider = conf.get('cassandra_auth_provider', None)
auth_kwargs = conf.get('cassandra_auth_kwargs', None)
if auth_provider and auth_kwargs:
auth_provider_class = getattr(cassandra.auth, auth_provider, None)
if not auth_provider_class:
raise ImproperlyConfigured(E_NO_SUCH_CASSANDRA_AUTH_PROVIDER)
self.auth_provider = auth_provider_class(**auth_kwargs)
self._cluster = None
self._session = None
self._write_stmt = None
self._read_stmt = None
self._lock = threading.RLock()
def _get_connection(self, write=False):
"""Prepare the connection for action.
Arguments:
write (bool): are we a writer?
"""
if self._session is not None:
return
self._lock.acquire()
try:
if self._session is not None:
return
# using either 'servers' or 'bundle_path' here:
if self.servers:
self._cluster = cassandra.cluster.Cluster(
self.servers, port=self.port,
auth_provider=self.auth_provider,
**self.cassandra_options)
else:
# 'bundle_path' is guaranteed to be set
self._cluster = cassandra.cluster.Cluster(
cloud={
'secure_connect_bundle': self.bundle_path,
},
auth_provider=self.auth_provider,
**self.cassandra_options)
self._session = self._cluster.connect(self.keyspace)
# We're forced to do concatenation below, as formatting would
# blow up on superficial %s that'll be processed by Cassandra
self._write_stmt = cassandra.query.SimpleStatement(
Q_INSERT_RESULT.format(
table=self.table, expires=self.cqlexpires),
)
self._write_stmt.consistency_level = self.write_consistency
self._read_stmt = cassandra.query.SimpleStatement(
Q_SELECT_RESULT.format(table=self.table),
)
self._read_stmt.consistency_level = self.read_consistency
if write:
# Only possible writers "workers" are allowed to issue
# CREATE TABLE. This is to prevent conflicting situations
# where both task-creator and task-executor would issue it
# at the same time.
# Anyway; if you're doing anything critical, you should
# have created this table in advance, in which case
# this query will be a no-op (AlreadyExists)
make_stmt = cassandra.query.SimpleStatement(
Q_CREATE_RESULT_TABLE.format(table=self.table),
)
make_stmt.consistency_level = self.write_consistency
try:
self._session.execute(make_stmt)
except cassandra.AlreadyExists:
pass
except cassandra.OperationTimedOut:
# a heavily loaded or gone Cassandra cluster failed to respond.
# leave this class in a consistent state
if self._cluster is not None:
self._cluster.shutdown() # also shuts down _session
self._cluster = None
self._session = None
raise # we did fail after all - reraise
finally:
self._lock.release()
def _store_result(self, task_id, result, state,
traceback=None, request=None, **kwargs):
"""Store return value and state of an executed task."""
self._get_connection(write=True)
self._session.execute(self._write_stmt, (
task_id,
state,
buf_t(self.encode(result)),
self.app.now(),
buf_t(self.encode(traceback)),
buf_t(self.encode(self.current_task_children(request)))
))
[документация] def as_uri(self, include_password=True):
return 'cassandra://'
def _get_task_meta_for(self, task_id):
"""Get task meta-data for a task by id."""
self._get_connection()
res = self._session.execute(self._read_stmt, (task_id, )).one()
if not res:
return {'status': states.PENDING, 'result': None}
status, result, date_done, traceback, children = res
return self.meta_from_decoded({
'task_id': task_id,
'status': status,
'result': self.decode(result),
'date_done': date_done,
'traceback': self.decode(traceback),
'children': self.decode(children),
})
def __reduce__(self, args=(), kwargs=None):
kwargs = {} if not kwargs else kwargs
kwargs.update(
{'servers': self.servers,
'keyspace': self.keyspace,
'table': self.table})
return super().__reduce__(args, kwargs)