fsq(7) is a standard for implementing queueing structures in POSIX file-systems. fsq provides a standard for both directory layouts and work-item naming, which allow for idempotent work-item construction, atomic enqueueing, and atomic completion.

fsq(1) is an interface for the file-system based queue-processing standard fsq(7). fsq(1) provides a variety of commands for enqueueing work, dispatching work and introspecting, auditing and repairing enqueued, failed, and finished work.

# cd /path/to/package/base/
# sudo python setup.py install

Each fsq queue conforms to the following directory structure:

The queue a_queue is installed to the default FSQ_ROOT, /var/fsq/. To enqueue a file to this queue, use the enqueue function:

```fs.enqueue('a_queue', ´/path/to/file', 'args', 'to', 'enqueue')```

or to enqueue a string, use the senqueue function:

```fsq.senqueue('a_queue', ´a string body for my work-item', 'args', 'to', 'enqueue')```

The queue directory within a_queue is the location where work-items are queued to. Following the above enqueue or senqueue function calls, you should be able to see 2 files in the q_queue/queue directory:

_20120710213904_0_13044_mss_0_args_to_enqueue
_20120710213904_1_13044_mss_0_args_to_enqueue
+|-----+------| + |-+-| |+| + |------+------|
|      |        |   |    |  |        |
|      |        |   |    |  |        +-> FSQ_DELIMITER seperated
|      |        |   |    |  |            arguments
|      |        |   |    |  +-> tries: number of failed attempts
|      |        |   |    |      to process
|      |        |   |    +-> hostname: the name of the host on
|      |        |   |        which the work-item was enqueued.
|      |        |   +-> pid of the process which enqueued the
|      |        |       work-item
|      |        +-> entropy: should a work-item be generated
|      |            with the same arguments, pid, hostname
|      |            and timestamp, entropy is incremented to
|      |            generate uniqueness.
|      +-> timestamp in FSQ_TIMEFMT format
+-> FSQ_DELIMITER used at enqueue time

The tmp directory within a_queue is a location for constructing work-items prior to enqueueing them to the queue directory. In the above enqueue and senqueue calls, the work-item files were initially con‐structed in tmp, then linked into queue and the tmp entry was removed.

The done directory within a_queue is a location for storing successfully completed work-items following work. Items may be marked as done, by using the done function (typically done during a scan):

for i in fsq.scan('a_queue'): fsq.done(i)

The function success may also be used:

for i in fsq.scan('a_queue'): fsq.success(i)

The done directory serves as a sort of book-keeping, but it should routinely be pruned, via cron or some such.

The fail directory within a_queue is a location for storing failed work-items following work. Items may be marked as failed, by using the fail function:

for i in fsq.scan('a_queue'):
  fsq.fail(i)

The fail_perm function may also be used:

for i in fsq.scan('a_queue'):
  try:
    raise Exception
  except:
    fsq.fail_perm(i)

permanent failure may also result if an work-item is older than, FSQ_TTL or if the work-item has been retried more than FSQ_MAX_TRIES by way of fail_tmp:

for i in fsq.scan('a_queue'):
  try:
    raise Exception
  except:
    fsq.fail_tmp(i)

Alternatively, retry may be used:

for i in fsq.scan('a_queue'):
  try:
    raise Exception
  except:
    fsq.retry(i)

The down file within a_queue is a file controlling wether or not a queue is available to be scanned. If down exists, the queue will not be scanned. down may be created by using the down function:

fsq.down('a_queue')

down may be removed by using the up function:

fsq.up('a_queue')

Queues with down may be scanned, by passing None or False to scan:

fsq.scan('a_queue', down=None)

The fsq suite and python library makes use of a number of FSQ_PREFIXED environment variables, which modify its behavior. Each environment variable is also available as a package-level constant.

Please refer to the fsq(7) manual page for a complete list.

Matthew Story <matt.story@axial.net>
Isaac (.ike) Levy <ike@blackskyresearch.net>
Will O'Meara <will.omeara@axial.net>

With Additional Contributions From:

Will Martino
Will Slippey
Jacob Yuan

And Thanks To:

William Baxter (For trigger, and for inspiring fsq)
Bruce Guenter (For nullmailer, featuring a simpler file-system queue)
Daniel J Bernstein (For QMail, inspiring trigger and nullmailer)