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.. _glossary:
Glossary
========
.. glossary::
:sorted:
acknowledged
Workers acknowledge messages to signify that a message has been
handled. Failing to acknowledge a message
will cause the message to be redelivered. Exactly when a
transaction is considered a failure varies by transport. In AMQP the
transaction fails when the connection/channel is closed (or lost),
but in Redis/SQS the transaction times out after a configurable amount
of time (the ``visibility_timeout``).
ack
Short for :term:`acknowledged`.
early acknowledgment
Task is :term:`acknowledged` just-in-time before being executed,
meaning the task won't be redelivered to another worker if the
machine loses power, or the worker instance is abruptly killed,
mid-execution.
Configured using :setting:`task_acks_late`.
late acknowledgment
Task is :term:`acknowledged` after execution (both if successful, or
if the task is raising an error), which means the task will be
redelivered to another worker in the event of the machine losing
power, or the worker instance being killed mid-execution.
Configured using :setting:`task_acks_late`.
early ack
Short for :term:`early acknowledgment`
late ack
Short for :term:`late acknowledgment`
ETA
"Estimated Time of Arrival", in Celery and Google Task Queue, etc.,
used as the term for a delayed message that should not be processed
until the specified ETA time. See :ref:`calling-eta`.
request
Task messages are converted to *requests* within the worker.
The request information is also available as the task's
:term:`context` (the ``task.request`` attribute).
calling
Sends a task message so that the task function is
:term:`executed <executing>` by a worker.
kombu
Python messaging library used by Celery to send and receive messages.
billiard
Fork of the Python multiprocessing library containing improvements
required by Celery.
executing
Workers *execute* task :term:`requests <request>`.
apply
Originally a synonym to :term:`call <calling>` but used to signify
that a function is executed by the current process.
context
The context of a task contains information like the id of the task,
it's arguments and what queue it was delivered to.
It can be accessed as the tasks ``request`` attribute.
See :ref:`task-request-info`
idempotent
Idempotence is a mathematical property that describes a function that
can be called multiple times without changing the result.
Practically it means that a function can be repeated many times without
unintended effects, but not necessarily side-effect free in the pure
sense (compare to :term:`nullipotent`).
Further reading: https://en.wikipedia.org/wiki/Idempotent
nullipotent
describes a function that'll have the same effect, and give the same
result, even if called zero or multiple times (side-effect free).
A stronger version of :term:`idempotent`.
reentrant
describes a function that can be interrupted in the middle of
execution (e.g., by hardware interrupt or signal), and then safely
called again later. Reentrancy isn't the same as
:term:`idempotence <idempotent>` as the return value doesn't have to
be the same given the same inputs, and a reentrant function may have
side effects as long as it can be interrupted; An idempotent function
is always reentrant, but the reverse may not be true.
cipater
Celery release 3.1 named after song by Autechre
(http://www.youtube.com/watch?v=OHsaqUr_33Y)
prefetch multiplier
The :term:`prefetch count` is configured by using the
:setting:`worker_prefetch_multiplier` setting, which is multiplied
by the number of pool slots (threads/processes/greenthreads).
`prefetch count`
Maximum number of unacknowledged messages a consumer can hold and if
exceeded the transport shouldn't deliver any more messages to that
consumer. See :ref:`optimizing-prefetch-limit`.
pidbox
A process mailbox, used to implement remote control commands.
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