Django-lrucache-backend

------------------

Implementation now based on the built in Django LocMemBackend as it switched
to an LRU strategy in [version 2.1](https://docs.djangoproject.com/en/2.1/topics/cache/local-memory-caching).

The only differences now are that keys are not validated against memcache rules,
and objects are not pickled.

* Dropped dependency on lru-dict, now using OrderedDict as per LocMemBackend
* Honour CULL_FREQUENCY setting as per LocMemBackend

Potential Compatability Issue:

Performance seems to be much better when CULL_FREQUENCY == MAX_ENTRIES as it
allows the LRU algorithm to work more effectively.

Benchmarks ::

========= ========= ========= ========= ========= ========= ========= =========
Timings for locmem (django) objects-500
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712424 72448 148.058us 185.013us 346.899us 8.008ms 113.785s
set 71473 0 152.826us 191.927us 360.012us 4.567ms 11.797s
delete 8095 0 144.958us 180.960us 339.031us 4.239ms 1.270s
Total 791992 126.852s
========= ========= ========= ========= ========= ========= ========= =========


========= ========= ========= ========= ========= ========= ========= =========
Timings for lrumem (lru-dict) objects-500
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712450 72398 99.897us 180.960us 307.083us 15.951ms 80.657s
set 71441 0 100.136us 180.006us 296.116us 12.349ms 8.059s
delete 8101 0 99.659us 180.960us 291.109us 890.970us 908.009ms
Total 791992 89.624s
========= ========= ========= ========= ========= ========= ========= =========


========= ========= ========= ========= ========= ========= ========= =========
Timings for lrumem (OrderedDict) objects-500
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712437 72379 105.381us 124.931us 249.147us 7.124ms 80.715s
set 71465 0 107.050us 126.839us 251.055us 4.267ms 8.204s
delete 8090 0 105.143us 123.739us 243.187us 2.800ms 911.312ms
Total 791992 89.831s
========= ========= ========= ========= ========= ========= ========= =========

Note, these benchmarks are a special once off showing the difference between the older
lru-dict dependency and the new OrderedDict implementation. It's also been updated
with performance stats from the latest Django implementation (2.2).

------------------

* Dropped support for Django 1.11
* Dropped support for Django < 2.2
* Dropped support for python 2

Benchmarks ::

PYTHONPATH="../:." python benchmark.py -r 500 --complex

========= ========= ========= ========= ========= ========= ========= =========
Timings for locmem-objects-500
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712444 72553 153.065us 207.186us 369.072us 6.758ms 119.826s
set 71457 0 159.025us 215.054us 378.132us 2.389ms 12.426s
delete 8091 0 150.919us 203.848us 365.019us 720.024us 1.335s
Total 791992 133.586s
========= ========= ========= ========= ========= ========= ========= =========


========= ========= ========= ========= ========= ========= ========= =========
Timings for lrumem-objects-500
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712419 72506 108.004us 193.834us 341.177us 5.191ms 90.436s
set 71482 0 108.242us 190.973us 321.150us 4.951ms 9.034s
delete 8091 0 108.004us 192.881us 323.772us 4.941ms 1.026s
Total 791992 100.496s
========= ========= ========= ========= ========= ========= ========= =========

------------------

* Dropped support for Django < 1.11
* Updated Django support for >= 2.1
* Removed python 3.3, 3.4, and 3.5 from build matrix. Support will be best effort.
* Changed locks from a Read-Write lock to an RLock, as a read lock is incorrect for LRU algorithm
* Changed benchmark script to use threads rather than multiprocessing so that locks
will be engaged during benchmarks.
* Now using poetry to build

Benchmarks ::

python benchmark.py -r 500 --complex

========= ========= ========= ========= ========= ========= ========= =========
Timings for lrumem-objects-500-2.0.0
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712436 72701 159.025us 302.076us 524.044us 49.870ms 130.832s
set 71473 0 159.979us 247.240us 470.161us 39.725ms 12.560s
delete 8083 0 157.833us 241.756us 473.976us 6.788ms 1.397s
Total 791992 144.789s
========= ========= ========= ========= ========= ========= ========= =========

------------------

* Don't validate the key
- delete P90: 20% improvement
- set P90: 17% improvement
- get P90: 10% improvement

Benchmarks ::

python benchmark.py -r 500 --complex

========= ========= ========= ========= ========= ========= ========= =========
Timings for lrumem-objects-500-0.2.0
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712827 99120 33.855us 59.843us 81.062us 37.626ms 28.899s
set 71262 0 35.048us 37.909us 73.195us 5.847ms 2.719s
delete 7903 0 32.902us 35.048us 63.896us 1.114ms 272.343ms
Total 791992 31.891s
========= ========= ========= ========= ========= ========= ========= =========

------------------

* Project comes online

Benchmarks ::

python benchmark.py -r 500 --complex

========= ========= ========= ========= ========= ========= ========= =========
Timings for locmem-objects-500
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712827 99120 51.022us 67.949us 127.077us 13.318ms 41.607s
set 71262 0 59.128us 66.042us 154.018us 6.350ms 4.693s
delete 7903 0 42.915us 46.015us 81.062us 3.040ms 361.492ms
Total 791992 46.661s
========= ========= ========= ========= ========= ========= ========= =========


========= ========= ========= ========= ========= ========= ========= =========
Timings for lrumem-objects-500
-------------------------------------------------------------------------------
Action Count Miss Median P90 P99 Max Total
========= ========= ========= ========= ========= ========= ========= =========
get 712827 99120 41.008us 66.996us 102.043us 29.211ms 34.952s
set 71262 0 42.915us 46.015us 84.162us 16.403ms 3.313s
delete 7903 0 40.054us 43.869us 80.824us 1.426ms 340.591ms
Total 791992 38.605s
========= ========= ========= ========= ========= ========= ========= =========