RedisBackend

Redis task result store.

Attributes

Attribute	Type	Description
ResultConsumer		The class used to consume task results from Redis.
redis	module	:pypi:redis client module.
connection_class_ssl	= redis.SSLConnection	The Redis connection class used when SSL is enabled, defaulting to redis.SSLConnection.
max_connections	int = null	Maximum number of connections in the pool.
supports_autoexpire	boolean = true	Indicates that the backend supports automatic expiration of keys via Redis EXPIRE commands.
supports_native_join	boolean = true	Indicates that the backend supports native join operations for chords.

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Constructor

Signature

def RedisBackend(
    host: string = null,
    port: int = null,
    db: int = null,
    password: string = null,
    max_connections: int = null,
    url: string = null,
    connection_pool: redis.ConnectionPool = null,
    **kwargs: dict
) - > null

Parameters

Name	Type	Description
host	string = null	The Redis server host. Can also be a connection URL.
port	int = null	The port number for the Redis server.
db	int = null	The Redis database index.
password	string = null	The password for Redis authentication.
max_connections	int = null	Maximum number of connections in the pool.
url	string = null	A full Redis connection URL.
connection_pool	redis.ConnectionPool = null	An existing Redis connection pool instance.
**kwargs	dict	Additional keyword arguments passed to the base class.

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Methods

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exception_safe_to_retry()

@classmethod
def exception_safe_to_retry(
    exc: Exception
) - > boolean

Determines if a raised exception is a connection-related error that can be safely retried.

Parameters

Name	Type	Description
exc	Exception	The exception instance to evaluate

Returns

Type	Description
boolean	True if the exception is in the known connection error classes, False otherwise

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retry_policy()

@classmethod
def retry_policy() - > dict

Retrieves the retry configuration for Redis operations, merging base policies with transport-specific options.

Returns

Type	Description
dict	A dictionary containing retry settings like max_retries and intervals

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on_task_call()

@classmethod
def on_task_call(
    producer: object,
    task_id: string
)

Initiates result consumption for a specific task ID if the current context allows non-blocking joins.

Parameters

Name	Type	Description
producer	object	The producer instance initiating the task call
task_id	string	The unique identifier of the task to start consuming

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get()

@classmethod
def get(
    key: string
) - > bytes

Fetches the raw value associated with a specific key from the Redis store.

Parameters

Name	Type	Description
key	string	The Redis key to retrieve

Returns

Type	Description
bytes	The raw data stored at the key, or None if the key does not exist

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mget()

@classmethod
def mget(
    keys: list
) - > list

Fetches multiple values from Redis in a single batch operation.

Parameters

Name	Type	Description
keys	list	A list of Redis keys to retrieve

Returns

Type	Description
list	A list of raw values corresponding to the provided keys

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ensure()

@classmethod
def ensure(
    fun: callable,
    args: tuple
) - > any

Executes a function with a retry policy to handle transient connection errors.

Parameters

Name	Type	Description
fun	callable	The function to execute with retry logic
args	tuple	Positional arguments to pass to the function

Returns

Type	Description
any	The return value of the executed function

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on_connection_error()

@classmethod
def on_connection_error(
    max_retries: int,
    exc: Exception,
    intervals: iterator,
    retries: int
) - > float

Logs a connection loss and calculates the next retry interval during a retry loop.

Parameters

Name	Type	Description
max_retries	int	The maximum number of allowed retry attempts
exc	Exception	The connection error that triggered this handler
intervals	iterator	An iterator providing the sequence of wait times between retries
retries	int	The current number of retry attempts already made

Returns

Type	Description
float	The number of seconds to wait before the next retry attempt

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set()

@classmethod
def set(
    key: string,
    value: string
) - > any

Stores a value in Redis with retry logic, ensuring the value does not exceed the maximum allowed size.

Parameters

Name	Type	Description
key	string	The Redis key where the value will be stored
value	string	The data to store; must be within Redis string size limits

Returns

Type	Description
any	The result of the underlying _set operation

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forget()

@classmethod
def forget(
    task_id: string
)

Removes a task's result from the store and cancels any active result consumption for that task.

Parameters

Name	Type	Description
task_id	string	The unique identifier of the task to forget

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delete()

@classmethod
def delete(
    key: string
)

Deletes a specific key from the Redis database.

Parameters

Name	Type	Description
key	string	The Redis key to remove

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incr()

@classmethod
def incr(
    key: string
) - > int

Increments the integer value of a key by one.

Parameters

Name	Type	Description
key	string	The Redis key to increment

Returns

Type	Description
int	The new value of the key after incrementing

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expire()

@classmethod
def expire(
    key: string,
    value: int
)

Sets a time-to-live (TTL) expiration on a specific Redis key.

Parameters

Name	Type	Description
key	string	The Redis key to expire
value	int	The number of seconds until the key expires

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add_to_chord()

@classmethod
def add_to_chord(
    group_id: string,
    result: any
)

Increments the counter tracking the number of completed parts in a chord group.

Parameters

Name	Type	Description
group_id	string	The unique identifier for the chord group
result	any	The result of the individual task part (unused in this implementation)

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set_chord_size()

@classmethod
def set_chord_size(
    group_id: string,
    chord_size: int
)

Stores the total number of expected tasks in a chord group to track completion.

Parameters

Name	Type	Description
group_id	string	The unique identifier for the chord group
chord_size	int	The total number of tasks in the chord header

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apply_chord()

@classmethod
def apply_chord(
    header_result_args: tuple,
    body: any
)

Saves the chord header metadata if it contains complex nested group results to preserve structure.

Parameters

Name	Type	Description
header_result_args	tuple	Arguments used to reconstruct the GroupResult for the chord header
body	any	The callback task to be executed when the chord is complete

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on_chord_part_return()

@classmethod
def on_chord_part_return(
    request: object,
    state: string,
    result: any
)

Handles the completion of a single chord task, updating the join state and triggering the callback if all parts are ready.

Parameters

Name	Type	Description
request	object	The task request object containing group and chord metadata
state	string	The execution state of the completed task part
result	any	The return value of the completed task part

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ConnectionPool()

@classmethod
def ConnectionPool() - > type

Property that returns the connection pool class, defaulting to the standard redis.ConnectionPool if not specified.

Returns

Type	Description
type	The class used to instantiate connection pools

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client()

@classmethod
def client() - > redis.StrictRedis

Property that provides a cached Redis client instance for performing operations.

Returns

Type	Description
redis.StrictRedis	The active Redis client for this backend

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