Retry Helpers#
- class redis.retry.Retry(backoff, retries, supported_errors=(<class 'redis.exceptions.ConnectionError'>, <class 'redis.exceptions.TimeoutError'>, <class 'socket.timeout'>))[source]#
Retry a specific number of times after a failure
Retry in Redis Standalone#
>>> from redis.backoff import ExponentialBackoff
>>> from redis.retry import Retry
>>> from redis.client import Redis
>>> from redis.exceptions import (
>>> BusyLoadingError,
>>> ConnectionError,
>>> TimeoutError
>>> )
>>>
>>> # Run 3 retries with exponential backoff strategy
>>> retry = Retry(ExponentialBackoff(), 3)
>>> # Redis client with retries on custom errors
>>> r = Redis(host='localhost', port=6379, retry=retry, retry_on_error=[BusyLoadingError, ConnectionError, TimeoutError])
>>> # Redis client with retries on TimeoutError only
>>> r_only_timeout = Redis(host='localhost', port=6379, retry=retry, retry_on_timeout=True)
As you can see from the example above, Redis client supports 3 parameters to configure the retry behaviour:
retry
:Retry
instance with a Backoff strategy and the max number of retriesretry_on_error
: list of Exceptions to retry onretry_on_timeout
: ifTrue
, retry onTimeoutError
only
If either retry_on_error
or retry_on_timeout
are passed and no retry
is given,
by default it uses a Retry(NoBackoff(), 1)
(meaning 1 retry right after the first failure).
Retry in Redis Cluster#
>>> from redis.backoff import ExponentialBackoff
>>> from redis.retry import Retry
>>> from redis.cluster import RedisCluster
>>>
>>> # Run 3 retries with exponential backoff strategy
>>> retry = Retry(ExponentialBackoff(), 3)
>>> # Redis Cluster client with retries
>>> rc = RedisCluster(host='localhost', port=6379, retry=retry, cluster_error_retry_attempts=2)
Retry behaviour in Redis Cluster is a little bit different from Standalone:
retry
:Retry
instance with a Backoff strategy and the max number of retries, default value isRetry(NoBackoff(), 0)
cluster_error_retry_attempts
: number of times to retry before raising an error whenTimeoutError
orConnectionError
orClusterDownError
are encountered, default value is3
Let’s consider the following example:
>>> from redis.backoff import ExponentialBackoff
>>> from redis.retry import Retry
>>> from redis.cluster import RedisCluster
>>>
>>> rc = RedisCluster(host='localhost', port=6379, retry=Retry(ExponentialBackoff(), 6), cluster_error_retry_attempts=1)
>>> rc.set('foo', 'bar')
the client library calculates the hash slot for key ‘foo’.
given the hash slot, it then determines which node to connect to, in order to execute the command.
during the connection, a
ConnectionError
is raised.because we set
retry=Retry(ExponentialBackoff(), 6)
, the client tries to reconnect to the node up to 6 times, with an exponential backoff between each attempt.even after 6 retries, the client is still unable to connect.
because we set
cluster_error_retry_attempts=1
, before giving up, the client starts a cluster update, removes the failed node from the startup nodes, and re-initializes the cluster.after the cluster has been re-initialized, it starts a new cycle of retries, up to 6 retries, with an exponential backoff.
if the client can connect, we’re good. Otherwise, the exception is finally raised to the caller, because we’ve run out of attempts.