A thread-safe disk based persistent queue in Python.
Project description
This project is based on the achievements of python-pqueue and queuelib
persist-queue implements a file-based queue and a serial of sqlite3-based queues. The goals is to achieve following requirements:
Disk-based: each queued item should be stored in disk in case of any crash.
Thread-safe: can be used by multi-threaded producers and multi-threaded consumers.
Recoverable: Items can be read after process restart.
Green-compatible: can be used in greenlet or eventlet environment.
While queuelib and python-pqueue cannot fulfil all of above. After some try, I found it’s hard to achieve based on their current implementation without huge code change. this is the motivation to start this project.
persist-queue use pickle object serialization module to support object instances. Most built-in type, like int, dict, list are able to be persisted by persist-queue directly, to support customized objects, please refer to Pickling and unpickling extension types(Python2) and Pickling Class Instances(Python3)
Requirements
Python 2.7 or Python 3.x.
Full support for Linux.
Windows support (with Caution if persistqueue.Queue is used).
Installation
from pypi
pip install persist-queuefrom source code
git clone https://github.com/peter-wangxu/persist-queue
cd persist-queue
python setup.py installBenchmark
Here is the result for writing/reading 10000 items to the disk comparing the sqlite3 and file queue.
- Environment:
OS: Windows 10
Disk: SATA3 SSD
RAM: 16 GiB
Transaction write (s) |
Bulk write (s) |
Transaction write/read (s) |
Bulk write/read (s) |
|
SQLite3 |
64.98 |
0.19 |
142.82 |
63.82 |
File |
89.68 |
85.78 |
101.37 |
85.76 |
Transaction refers to commit the change to disk on every write.
Bulk refers to only commit the change to disk on last write.
To see the real performance on your host, run the script under benchmark/run_benchmark.py:
python benchmark/run_benchmark.pyExamples
Example usage with a SQLite3 based queue
>>> import persistqueue
>>> q = persistqueue.SQLiteQueue('mypath', auto_commit=True)
>>> q.put('str1')
>>> q.put('str2')
>>> q.put('str3')
>>> q.get()
'str1'
>>> del qClose the console, and then recreate the queue:
>>> import persistqueue
>>> q = persistqueue.SQLiteQueue('mypath', auto_commit=True)
>>> q.get()
'str2'
>>>Example usage with a file based queue
>>> from persistqueue import Queue
>>> q = Queue("mypath")
>>> q.put('a')
>>> q.put('b')
>>> q.put('c')
>>> q.get()
'a'
>>> q.task_done()Close the python console, and then we restart the queue from the same path,
>>> from persistqueue import Queue
>>> q = Queue('mypath')
>>> q.get()
'b'
>>> q.task_done()Example usage with a SQLite3 based dict
>>> from persisitqueue import PDict
>>> q = PDict("testpath", "testname")
>>> q['key1'] = 123
>>> q['key2'] = 321
>>> q['key1']
123
>>> len(q)
2
>>> del q['key1']
>>> q['key1']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "persistqueue\pdict.py", line 58, in __getitem__
raise KeyError('Key: {} not exists.'.format(item))
KeyError: 'Key: key1 not exists.'Close the console and restart the PDict
>>> from persisitqueue import PDict
>>> q = PDict("testpath", "testname")
>>> q['key2']
321Multi-thread usage for SQLite3 based queue
from persistqueue import FIFOSQLiteQueue
q = FIFOSQLiteQueue(path="./test", multithreading=True)
def worker():
while True:
item = q.get()
do_work(item)
for i in range(num_worker_threads):
t = Thread(target=worker)
t.daemon = True
t.start()
for item in source():
q.put(item)multi-thread usage for Queue
from persistqueue import Queue
q = Queue()
def worker():
while True:
item = q.get()
do_work(item)
q.task_done()
for i in range(num_worker_threads):
t = Thread(target=worker)
t.daemon = True
t.start()
for item in source():
q.put(item)
q.join() # block until all tasks are donePerformance impact
Since persistqueue v0.3.0, a new parameter auto_commit is introduced to tweak the performance for sqlite3 based queues as needed. When specify auto_commit=False, user needs to perform queue.task_done() to persist the changes made to the disk since last task_done invocation.
Tests
persist-queue use tox to trigger tests.
to trigger tests based on python2.7/python3.x, use:
tox -e py27tox -e py34tox -e py35tox -e py36to trigger pep8 check, use:
tox -e pep8pyenv is usually a helpful tool to manage multiple versions of Python.
Caution
Currently, the atomic operation is not supported on Windows due to the limitation of Python’s os.rename, That’s saying, the data in persistqueue.Queue could be in unreadable state when an incidental failure occurs during Queue.task_done.
DO NOT PUT ANY CRITICAL DATA ON persistqueue.QUEUE WHEN RUNNING ON WINDOWS.
Contribution
Simply fork this repo and send PR for your code change(also tests to cover your change), remember to give a title and description of your PR. I am willing to enhance this project with you :).
License
FAQ
sqlite3.OperationalError: database is locked is raised.
persistquest open 2 connections for the db if multithreading=True, the SQLite database is locked until that transaction is committed. The timeout parameter specifies how long the connection should wait for the lock to go away until raising an exception. Default time is 10, increase timeout when creating the queue if above error occurs.
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