django-cachalot¶

Requirements¶

• Django 1.6 or 1.7

• Python 2.6, 2.7, 3.2, 3.3, or 3.4

• a cache configured as default with one of these backends:

  • django-redis

  • memcached (using either python-memcached or pylibmc (but pylibmc is only supported

    with Django >= 1.7))

  • filebased (only with Django >= 1.7 as it was not thread-safe before)

  • locmem (but it’s not shared between processes, see Limits)

• one of these databases:

  • PostgreSQL

  • SQLite

  • MySQL (but you probably don’t need django-cachalot in this case,

    see Limits)

Usage¶

1. pip install django-cachalot
2. Add 'cachalot', to your INSTALLED_APPS
3. Be aware of the few limits
4. If you use django-debug-toolbar, you can add 'cachalot.panels.CachalotPanel', to your DEBUG_TOOLBAR_PANELS
5. Enjoy!

Settings¶

from django.conf import settings
from django.test.utils import override_settings

with override_settings(CACHALOT_ENABLED=False):
    # SQL queries are not cached in this block

@override_settings(CACHALOT_CACHE='another_alias')
def your_function():
    # What’s in this function uses another cache

# Globally disables SQL caching until you set it back to True
settings.CACHALOT_ENABLED = False

Locmem¶

Locmem is a just a dict stored in a single Python process. It’s not shared between processes, so don’t use locmem with django-cachalot in a multi-processes project, if you use RQ or Celery for instance.

MySQL¶

This database software already provides by default something like django-cachalot: MySQL query cache. Django-cachalot will slow down your queries if that query cache is enabled. If it’s not enabled, django-cachalot will make queries much faster. But you should probably better enable the query cache instead.

Raw SQL queries¶

By default, django-cachalot tries to invalidate its cache after a raw query. It detects if the raw query contains UPDATE, INSERT or DELETE, and then invalidates the tables contained in that query by comparing with models registered by Django.

This is quite robust, so if a query is not invalidated automatically by this system, please send a bug report. In the meantime, you can use the API to manually invalidate the tables where data has changed.

However, this simple system can be too efficient in some cases and lead to unwanted extra invalidations. In such cases, you may want to partially disable this behaviour by dynamically overriding settings to set CACHALOT_INVALIDATE_RAW to False. After that, use the API to manually invalidate the tables you modified.

For version 1.0¶

• Cache raw queries
• Test multi-location caches
• Add a management command to invalidate everything

Reverse engineering¶

It’s a lot of Django reverse engineering combined with a strong test suite. Such a test suite is crucial for a reverse engineering project. If some important part of Django changes and breaks the expected behaviour, you can be sure that the test suite will fail.

Monkey patching¶

django-cachalot modifies Django in place during execution to add a caching tool just before SQL queries are executed. We detect which cache keys must be removed when some data is created/changed/deleted on the database.

0.9.0¶

Added:

• Caches all queries implying Queryset.extra
• Invalidates raw queries
• Adds a simple API containing: invalidate_tables, invalidate_models, invalidate_all
• Adds file-based cache support for Django 1.7
• Adds a setting to choose if random queries must be cached
• Adds 2 settings to customize how cache keys are generated
• Adds a django-debug-toolbar panel
• Adds a benchmark

Fixed:

• Rewrites invalidation for a better speed & memory performance
• Fixes a stale cache issue occurring when an invalidation is done exactly during a SQL request on the invalidated table(s)
• Fixes a stale cache issue occurring after concurrent transactions
• Uses an infinite timeout

Removed:

• Simplifies cachalot_settings and forbids its use or modification

0.8.1¶

• Fixes an issue with pip if Django is not yet installed

0.8.0¶

• Adds multi-database support
• Adds invalidation when altering the DB schema using migrate, syncdb, flush, loaddata commands (also invalidates South, if you use it)
• Small optimizations & simplifications
• Adds several tests

0.7.0¶

• Adds thread-safety
• Optimizes the amount of cache queries during transaction

0.6.0¶

• Adds memcached support

0.5.0¶

• Adds CACHALOT_ENABLED & CACHALOT_CACHE settings
• Allows settings to be dynamically overridden using cachalot_settings
• Adds some missing tests

0.4.1¶

• Fixes pip install.

0.4.0 (install broken)¶

• Adds Travis CI and adds compatibility for:
  • Django 1.6 & 1.7
  • Python 2.6, 2.7, 3.2, 3.3, & 3.4
  • locmem & Redis
  • SQLite, PostgreSQL, MySQL

0.3.0¶

• Handles transactions
• Adds lots of tests for complex cases

0.2.0¶

• Adds a test suite
• Fixes invalidation for data creation/deletion
• Stops caching on queries defining select or where arguments with QuerySet.extra

0.1.0¶

Prototype simply caching all SQL queries reading the database and trying to invalidate them when SQL queries modify the database.

Has issues invalidating deletions and creations. Also caches QuerySet.extra queries but can’t reliably invalidate them. No transaction support, no test, no multi-database support, etc.