saferedisqueue 1.0.1

A small wrapper around Redis that provides access to a FIFO queue.

==============
saferedisqueue
==============

A small wrapper around `Redis <http://www.redis.io>`_ (using the "standard"
`Python redis client lib <https://pypi.python.org/pypi/redis>`_) that provides
access to a FIFO queue and allows upstream code to mark pop'ed items as
processed successfully (ACK'ing) or unsucessfully (FAIL'ing).

Failed items are automatically requeued. Addionally a backup is kept for items
that were neither ack'ed nor fail'ed, i.e. in case the consumer crashes. The
backup items will be requeued as soon as one of the consumer(s) comes up
again.

All actions are atomic and it is safe to have multiple producers and consumers
accessing the same queue concurrently.

.. attention:: Currently it only works with Redis 2.4. The code should be easy
to adapt to 2.6 — pull requests and patches accepted ;-)


Usage as a library
==================

>>> queue = SafeRedisQueue(name='test')
>>> queue.push("Hello World")
>>> queue.push("Foo bar")
>>> queue.pop()
('595d43b2-2e49-4e96-a1d2-0848d1c7f0d3', 'Hello World')
>>> queue.pop()
('1df060eb-b578-499d-bede-20db9da8184e', 'Foo bar')


ACK'ing and FAIL'ing
--------------------

>>> queue.push("Good stuff")
>>> queue.push("Bad stuff")
>>> uid_good, payload_good = queue.pop()
>>> uid_bad, payload_bad = queue.pop()
...
# process the payloads...
...
>>> queue.ack(uid_good) # done with that one
>>> queue.fail(uid_bad) # something didn't work out with that one, let's requeue
>>> uid, payload = queue.pop() # pop again; we get the requeued payload again
>>> uid == uid_bad
True
...
# try again
...
>>> queue.ack(uid) # now it worked; ACK the stuff now


pop timeout
-----------

`SafeRedisQueue.pop` accepts a timeout parameter:

- 0 (the default) blocks forever, waiting for items
- a positive number blocks that amount of seconds
- a negative timeout disables blocking


Constructor parameters
----------------------

`SafeRedisQueue` accepts ``*args, **kwargs`` and passes them to
`redis.StrictRedis`, so use whatever you need.

*Two exceptions*, use these in the keyword arguments to configure `SafeRedisQueue` itself:

`name`
A prefix used for the keys in Redis. Default: "0", which creates the
following keys in your Redis DB:

- srq:0:items
- srq:0:queue
- srq:0:ackbuf
- srq:0:backup
- srq:0:backuplock

`autoclean_interval`
An interval in seconds (default: 60) at which *unacknowledged* items are
requeued automatically. (They are moved from the internal ackbuf and backup data
structures to the queue again.)

Pass ``None`` to disable autocleaning. It's enabled by default!


Command line usage
==================

For quick'n'dirty testing, you can use the script from the command line to put stuff into the queue::

$ echo "Hello World" | python saferedisqueue.py producer

...and get it out again::

$ python saferedisqueue.py consumer
cbdabbc8-1c0f-4eb0-8733-fdb62a9c0fa6 Hello World


=======
Changes
=======

1.0.1 - 2013-06-26
------------------

- Changed dependency on redis to require at least version 2.4.10 as
redis.StrictRedis, which we use, was only introduced in that version.
This should not affect anyone negatively as you wouldn't have to be able
to use saferedisqueue at all if your project or package used an older
version so far.
(Thanks Telofy!)


1.0.0 - 2013-06-05
------------------

- Released as open-source under 3-clause BSD license. Code identical to 0.3.0.


0.3.0 - 2012-05-22
------------------

- The constructor now accepts an "autoclean_interval" value to set the interval
at which the ackbuf -> backup rotation and backup requeuing happens.
Setting the value to `None` disables autoclean completely.
Default: 60 (seconds).


0.2.2 - 2012-03-29
------------------

- Negative timeout makes .pop() non-blocking.


0.2.1 - 2012-03-09
------------------

- Added setup.py and publish it on our internal package directory.


0.2.0 - 2012-03-08
------------------

- Renamed methods ("push_item" -> "push" etc.)
- New autoclean method that is called on every .pop()
- Internal: New names for keys in the redis db.