litequeue 0.1

Simple queue built on top of SQLite

litequeue

Queue implemented on top of SQLite

Why?

You can use this to implement a persistent queue. It also has extra timing metrics for the tasks and the api to set a task as done lets you specifiy the task_id to set as done.

Since it's all based on SQLite / SQL, it is easily extendable.

Installation

Differences with a normal Python queue.Queue

• Persistence
• Different API to set tasks as done (you tell it which task_id to set as done)
• Timing metrics. As long as tasks are still in the queue or not pruned, you can see how long they have been there or how long they took to finish.
• Easy to extend using SQL

Examples

The examples are taken from the tests in tests.ipynb

from litequeue import SQLQueue

TEST_1 = "key_test_1"
TEST_2 = "key_test_2"

q = SQLQueue(":memory:")

q.put("hello")
q.put("world")
q.put("foo")
q.put("bar")
# 4  <- ID of the last row modified

q.pop()
# {'message': 'hello', 'task_id': '7da620ac542acd76c806dbcf00218426'}

print(q)


#    SQLQueue(dbname=':memory:', items=[{'done_time': None,
#      'in_time': 1612711137,
#      'lock_time': 1612711137,
#      'message': 'hello',
#      'status': 1,
#      'task_id': '7da620ac542acd76c806dbcf00218426'},
#       ...

# pop remaining
for _ in range(3):
    q.pop()


assert q.pop() is None

q.put("hello")
q.put("world")
q.put("foo")
q.put("bar")

# 8 <- ID of the last row modified

task = q.pop()

assert task["message"] == "hello"

q.peek()


#    {'message': 'world',
#     'task_id': '44cbc85f12b62891aa596b91f14183e5',
#     'status': 0,
#     'in_time': 1612711138,
#     'lock_time': None,
#     'done_time': None}


# next one that is free
assert q.peek()["message"] == "world"

# status = 0 = free
assert q.peek()["status"] == 0

# -> back to our previous task <-

task["message"], task["task_id"]

# ('hello', 'c9b9ef76e3a77cc66dd749d485613ec1')   

q.done(task["task_id"])

# 8 <- ID of the last row modified

q.get(task["task_id"])

#    {'message': 'hello',
#     'task_id': 'c9b9ef76e3a77cc66dd749d485613ec1',
#     'status': 2,   <---- status is now 2 (DONE)
#     'in_time': 1612711138,
#     'lock_time': 1612711138,
#     'done_time': 1612711138}


already_done = q.get(task["task_id"])

# stauts = 2 = done
assert already_done["status"] == 2

in_time = already_done["in_time"]
lock_time = already_done["lock_time"]
done_time = already_done["done_time"]

assert done_time >= lock_time >= in_time
print(
    f"Task {already_done['task_id']} took {done_time - lock_time} seconds to get done and was in the queue for {done_time - in_time} seconds"
)

# Task c9b9ef76e3a77cc66dd749d485613ec1 took 0 seconds to get done and was in the queue for 0 seconds

# the queue size ignores the finished items

assert q.qsize() == 7

next_one_msg = q.peek()["message"]
next_one_id = q.peek()["task_id"]

task = q.pop()

assert task["message"] == next_one_msg
assert task["task_id"] == next_one_id

# remove finished items
q.prune()

print(q)


#    SQLQueue(dbname=':memory:', items=[{'done_time': None,
#      'in_time': 1612711137,
#      'lock_time': 1612711137,
#      'message': 'hello',
#      'status': 1,
#      'task_id': '7da620ac542acd76c806dbcf00218426'},
#     {'done_time': None,
#      'in_time': 1612711137,
#      'lock_time': 1612711137,
#      'message': 'world',
#      'status': 1,
#      'task_id': 'a593292cfc8d2f3949eab857eafaf608'},
#     {'done_time': None,
#      'in_time': 1612711137,
#      'lock_time': 1612711137,
#      'message': 'foo',
#      'status': 1,
#      'task_id': '17e843a29770df8438ad72bbcf059bf5'},
#     ...

from string import ascii_lowercase, printable
from random import choice


def random_string(string_length=10, fuzz=False, space=False):
    """Generate a random string of fixed length """
    letters = ascii_lowercase
    letters = letters + " " if space else letters
    if fuzz:
        letters = printable
    return "".join(choice(letters) for i in range(string_length))

q = SQLQueue(":memory:", maxsize=50)

for i in range(50):

    q.put(random_string(20))

assert q.qsize() == 50

An error is raised when the queue has reached its size limit

import sqlite3

try:
    q.put(random_string(20))
except sqlite3.IntegrityError: # max len reached
    print("test pass")

# test pass

q.pop()

#    {'message': 'aktabyjadzrsohlitnei',
#     'task_id': '08b201c31099a296ef37f23b5257e5b6'}

q.put("hello")

# 51


# Check if a queue is empty
assert q.empty() == False

q2 = SQLQueue(":memory:")

assert q2.empty() == True

Benchmarks

Inserting items in the queue.

import gc

In-memory SQL queue

q = SQLQueue(":memory:", maxsize=None)

gc.collect()

# %%timeit -n10000 -r7

q.put(random_string(20))

# 40.2 µs ± 12 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

q.qsize()

# 70000

Standard python queue.

from queue import Queue

q = Queue()

gc.collect()

# %%timeit -n10000 -r7

q.put(random_string(20))

# 21.9 µs ± 3.57 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

Persistent SQL queue

q = SQLQueue("test.queue", maxsize=None)

gc.collect()

# %%timeit -n10000 -r7

q.put(random_string(20))

# 161 µs ± 5.36 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

assert q.conn.isolation_level is None

Creating, popping and setting tasks as done.

q = Queue()

gc.collect()

# %%timeit -n10000 -r7

tid = random_string(20)

q.put(tid)

q.get()

q.task_done()

# 27 µs ± 3.69 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

q = SQLQueue(":memory:", maxsize=None)

gc.collect()

# %%timeit -n10000 -r7

tid = random_string(20)

q.put(tid)

task = q.pop()

q.done(task["task_id"])

# 80.2 µs ± 4.02 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

Meta

Ricardo Ander-Egg Aguilar – @ricardoanderegg –

• ricardoanderegg.com
• github.com/polyrand
• linkedin.com/in/ricardoanderegg

Distributed under the MIT license. See LICENSE for more information.

Contributing

The only hard rules for the project are:

• No extra dependencies allowed
• No extra files, everything must be inside the main module's .py file.
• Tests must be inside the tests.ipynb notebook.