Metadata-Version: 2.1
Name: psycopg2_mq
Version: 0.7.0
Summary: A message queue written around PostgreSQL.
Home-page: https://github.com/mmerickel/psycopg2_mq
Author: Michael Merickel
Author-email: oss@m.merickel.org
License: UNKNOWN
Description: ===========
        psycopg2_mq
        ===========
        
        .. image:: https://img.shields.io/pypi/v/psycopg2_mq.svg
            :target: https://pypi.org/pypi/psycopg2_mq
        
        ``psycopg2_mq`` is a message queue implemented on top of
        `PostgreSQL <https://www.postgresql.org/>`__,
        `SQLAlchemy <https://www.sqlalchemy.org/>`__, and
        `psycopg2 <http://initd.org/psycopg/>`__.
        
        Currently the library provides only the low-level constructs that can be used
        to build a multithreaded worker system. It is broken into two components:
        
        - ``psycopg2_mq.MQWorker`` - a reusable worker object that manages a
          single-threaded worker that can accept jobs and execute them. An application
          should create worker per thread. It supports an API for thread-safe graceful
          shutdown.
        
        - ``psycopg2_mq.MQSource`` - a source object providing a client-side API for
          invoking and querying job states.
        
        Data Model
        ==========
        
        Queues
        ------
        
        Workers run jobs defined in queues. Currently each queue will run jobs
        concurrently, while a future version may support serial execution on a
        per-queue basis. Each registered queue should contain an ``execute_job(job)``
        method.
        
        Jobs
        ----
        
        The ``execute_job`` method of a queue is passed a ``Job`` object containing
        the following attributes:
        
        - ``id``
        - ``queue``
        - ``method``
        - ``args``
        - ``cursor``
        
        As a convenience, there is an ``extend(**kw)`` method which can be used to
        add extra attributes to the object. This is useful in individual queues to
        define a contract between a queue and its methods.
        
        Cursors
        -------
        
        A ``Job`` can be scheduled with a ``cursor_key``. There can only be one
        pending job and one running job for any cursor. New jobs scheduled while
        another one is pending will be ignored and the pending job is returned.
        
        A ``job.cursor`` dict is provided to the workers containing the cursor data,
        and is saved back to the database when the job is completed. This effectively
        gives jobs some persistent, shared state, and serializes all jobs over a given
        cursor.
        
        Delayed Jobs
        ------------
        
        A ``Job`` can be delayed to run in the future by providing a ``datetime``
        object to the ``when`` argument. This, along with a cursor key, can provide a
        nice throttle on how frequently a job runs. For example, delay jobs to run
        in 30 seconds with a ``cursor_key`` and any jobs that are scheduled in the
        meantime will be dropped. The assumption here is that the arguments are
        constant and data for execution is in the cursor or another table. As a last
        resort, a ``conflict_resolver`` callback can be used to modify properties of
        the job when arguments cannot be constant.
        
        Schedules
        ---------
        
        A ``JobSchedule`` can be defined which supports
        `RFC 5545 <https://tools.ietf.org/html/rfc5545>`__ ``RRULE`` schedules. These
        are powerful and can support timezones, frequencies based on calendars as well
        as simple recurring rules from an anchor time using ``DTSTART``. Cron jobs
        can be converted to this syntax for simpler scenarios.
        
        ``psycopg2-mq`` workers will automatically negotiate which worker is responsible
        for managing schedules so clustered workers should operate as expected.
        
        Example Worker
        ==============
        
        .. code-block:: python
        
            from psycopg2_mq import (
                MQWorker,
                make_default_model,
            )
            from sqlalchemy import (
                MetaData,
                create_engine,
            )
            import sys
        
            class EchoQueue:
                def execute_job(self, job):
                    return f'hello, {job.args["name"]} from method="{job.method}"'
        
            if __name__ == '__main__':
                engine = create_engine(sys.argv[1])
                metadata = MetaData()
                model = make_default_model(metadata)
                worker = MQWorker(
                    engine=engine,
                    queues={
                        'echo': EchoQueue(),
                    },
                    model=model,
                )
                worker.run()
        
        Example Source
        ==============
        
        .. code-block:: python
        
            engine = create_engine()
            metadata = MetaData()
            model = make_default_model(metadata)
            session_factory = sessionmaker()
            session_factory.configure(bind=engine)
        
            dbsession = session_factory()
            with dbsession.begin():
                mq = MQSource(
                    dbsession=dbsession,
                    model=model,
                )
                job = mq.call('echo', 'hello', {'name': 'Andy'})
                print(f'queued job={job.id}')
        
        
        0.7.0 (2022-03-03)
        ==================
        
        - Fix a corner case with lost jobs attached to cursors. In scenarios where
          multiple workers are running, if one loses a database connection then the
          other is designed to notice and mark jobs lost. However, it's possible the
          job is not actually lost and the worker can then recover after resuming
          its connection, and marking the job running again. In this situation, we
          do not want another job to begin on the same cursor. To fix this issue,
          new jobs will not be run if another job is marked lost on the same cursor.
          You will be required to recover the job by marking it as not lost (probably
          failed) first to unblock the rest of the jobs on the cursor.
        
        0.6.2 (2022-03-01)
        ==================
        
        - Prioritize maintenance work higher than running new jobs.
          There was a chicken-and-egg issue where a job would be marked running
          but needs to be marked lost. However marking it lost is lower priority than
          trying to start new jobs. In the case where a lot of jobs were scheduled
          at the same time, the worker always tried to start new jobs and didn't
          run the maintenance so the job never got marked lost, effectively blocking
          the queue.
        
        0.6.1 (2022-01-15)
        ==================
        
        - Fix a bug introduced in the 0.6.0 release when scheduling new jobs.
        
        0.6.0 (2022-01-14)
        ==================
        
        - [breaking] Add model changes to mark jobs as collapsible.
        
        - [breaking] Add model changes to the cursor index.
        
        - Allow multiple pending jobs to be scheduled on the same cursor if either:
        
          1. The queue or method are different from existing pending jobs on the cursor.
        
          2. ``collapse_on_cursor`` is set to ``False`` when scheduling the job.
        
        0.5.7 (2021-03-07)
        ==================
        
        - Add a ``schedule_id`` attribute to the job context for use in jobs that want
          to know whether they were executed from a schedule or not.
        
        0.5.6 (2021-02-28)
        ==================
        
        - Some UnicodeDecodeError exceptions raised from jobs could trigger a
          serialization failure (UntranslatableCharacter) because it would contain
          the sequence ``\u0000``` which, while valid in Python, is not allowed
          in postgres. So when dealing with the raw bytes, we'll decode it with
          the replacement character that can be properly stored. Not ideal, but
          better than failing to store the error at all.
        
        0.5.5 (2021-01-22)
        ==================
        
        - Fixed some old code causing the worker lock to release after a job
          completed.
        
        0.5.4 (2021-01-20)
        ==================
        
        - Log at the error level when marking a job as lost.
        
        0.5.3 (2021-01-11)
        ==================
        
        - Copy the ``schedule_id`` information to retried jobs.
        
        0.5.2 (2021-01-11)
        ==================
        
        - [breaking] Require ``call_schedule`` to accept an id instead of an object.
        
        0.5.1 (2021-01-09)
        ==================
        
        - Drop the ``UNIQUE`` constraint on the background job ``lock_id`` column.
        
        0.5 (2021-01-09)
        ================
        
        - Add a scheduler model with support for emitting periodic jobs based on
          RRULE syntax.
          See https://github.com/mmerickel/psycopg2_mq/pull/11
        
        - Enable the workers to coordinate on a per-queue basis who is in control
          of scheduling jobs.
          See https://github.com/mmerickel/psycopg2_mq/pull/12
        
        - Reduce the number of advisory locks held from one per job to one per worker.
          See https://github.com/mmerickel/psycopg2_mq/pull/12
        
        0.4.5 (2020-12-22)
        ==================
        
        - Use column objects in the insert statement to support ORM-level synonyms,
          enabling the schema to have columns with different names.
        
        0.4.4 (2019-11-07)
        ==================
        
        - Ensure the advisory locks are released when a job completes.
        
        0.4.3 (2019-10-31)
        ==================
        
        - Ensure maintenance (finding lost jobs) always runs at set intervals defined
          by the ``timeout`` parameter.
        
        0.4.2 (2019-10-30)
        ==================
        
        - Recover active jobs when the connection is lost by re-locking them
          and ensuring they are marked running.
        
        0.4.1 (2019-10-30)
        ==================
        
        - Attempt to reconnect to the database after losing the connection.
          If the reconnect attempt fails then crash.
        
        0.4 (2019-10-28)
        ================
        
        - Add a ``worker`` column to the ``Job`` model to track what worker
          is handling a job.
        
        - Add an optional ``name`` argument to ``MQWorker`` to name the worker -
          the value will be recorded in each job.
        
        - Add a ``threads`` argument (default=``1``) to ``MQWorker`` to support
          handling multiple jobs from the same worker instance instead of making a
          worker per thread.
        
        - Add ``capture_signals`` argument (default=``True``) to ``MQWorker`` which
          will capture ``SIGTERM``, ``SIGINT`` and ``SIGUSR1``. The first two will
          trigger graceful shutdown - they will make the process stop handling new
          jobs while finishing active jobs. The latter will dump to ``stderr`` a
          JSON dump of the current status of the worker.
        
        0.3.3 (2019-10-23)
        ==================
        
        - Only save a cursor update if the job is completed successfully.
        
        0.3.2 (2019-10-22)
        ==================
        
        - Mark lost jobs during timeouts instead of just when a worker starts in order
          to catch them earlier.
        
        0.3.1 (2019-10-17)
        ==================
        
        - When attempting to schedule a job with a cursor and a ``scheduled_time``
          earlier than a pending job on the same cursor, the job will be updated to
          run at the earlier time.
        
        - When attempting to schedule a job with a cursor and a pending job already
          exists on the same cursor, a ``conflict_resolver`` function may be
          supplied to ``MQSource.call`` to update the job properties, merging the
          arguments however the user wishes.
        
        0.3 (2019-10-15)
        ================
        
        - Add a new column ``cursor_snapshot`` to the ``Job`` model which will
          contain the value of the cursor when the job begins.
        
        0.2 (2019-10-09)
        ================
        
        - Add cursor support for jobs. This requires a schema migration to add
          a ``cursor_key`` column, a new ``JobCursor`` model, and some new indices.
        
        0.1.6 (2019-10-07)
        ==================
        
        - Support passing custom kwargs to the job in ``psycopg2_mq.MQSource.call``
          to allow custom columns on the job table.
        
        0.1.5 (2019-05-17)
        ==================
        
        - Fix a regression when serializing errors with strings or cycles.
        
        0.1.4 (2019-05-09)
        ==================
        
        - More safely serialize exception objects when jobs fail.
        
        0.1.3 (2018-09-04)
        ==================
        
        - Rename the thread to contain the job id while it's handling a job.
        
        0.1.2 (2018-09-04)
        ==================
        
        - Rename ``Job.params`` to ``Job.args``.
        
        0.1.1 (2018-09-04)
        ==================
        
        - Make ``psycopg2`` an optional dependency in order to allow apps to depend
          on ``psycopg2-binary`` if they wish.
        
        0.1 (2018-09-04)
        ================
        
        - Initial release.
        
Keywords: psycopg2,postgres,postgresql
Platform: UNKNOWN
Classifier: Development Status :: 4 - Beta
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: MIT License
Classifier: Natural Language :: English
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.6
Classifier: Programming Language :: Python :: 3.7
Classifier: Programming Language :: Python :: 3.8
Classifier: Programming Language :: Python :: 3.9
Classifier: Programming Language :: Python :: Implementation :: CPython
Requires-Python: >=3.6
Provides-Extra: testing
