[TYPO3-core] FYI: Added feature #16410: [Caching framework] Implement redis as cache backend

[Christian Kuhn]

The following patch was committed to trunk rev. 9390

Type: Feature

BT: http://bugs.typo3.org/view.php?id=16410

Branches: trunk

Problem:
Redis [1] is a noSQL database with very good scaling characteristics in 
relation to the amount of entries and data size. This makes redis 
perfectly fit our needs as a caching framework backend. redis is a 
key-value store like memcache, but does not have the cache integrity 
problems we face with memcache if used right.

Solution:
Implement redis as a cache backend using the phpredis PHP module [2]

Notes:
- This is the v4 backport of [3], which was merged to FLOW3 with git 
revisions 7f11528521db7d04845e652d948a429b93f2f2e9, 
923af427d12e5c7e1d7420ac547a8bfeb9f14af5 and 
dd78aca101a46f41bbbc3376b2524ff0885e91f6
- In addition to FLOW3 version, the API methods findIdentifiersByTags() 
and flushByTags() where added to comply to v4 interfaces.
- The code has pretty high unit test code coverage, far more than all 
other existing cache backends.
- Configure the scheduler caching framework garbage collection task to 
run for redis backends once in a while to free unused memory.

Available backend options:
- database -> database number (should be set!)
- compression -> enable zlib data compression, identical to db backend 
(TRUE / FALSE, default: FALSE)
- compressionLevel -> zlib compression level, identical to db backend, 
integer -1 (default zlib compression), 0 .. 9 (default: -1)
- hostname -> server hostname
- port -> server port
- password -> server password

Thanks to:
- Christopher Hlubek for the initial implementation with ext:rediscache
- Andre Heydt for help with the big O notation for all relevant methods
- FLOW3 team for quick reviews and merge to make this feature core ready 
before feature freeze of 4.5

Warnings:
- redis and phpredis are young projects with high development speed. In 
future internal structures might change!
- This implementation was tested with:
-- redis 2.0.x, redis git revision 9fd01051bf8400babcca73a76a67dfc1847633ff
-- phpredis git revision 12769b03c8ec17b25573e0453003712011bba241
- redis scales far better than every other existing cache backend with 
big data sizes and tons of cache entries, but only if redis is fully RAM 
driven. Make sure to tune your redis settings for production use, there 
are plenty of options, see redis.conf for details.
- Be aware that redis can be _very_ memory hungry. Again: It's important 
to configure redis options to suite your production needs.
- Make sure every cache is assigned to an own redis database. flush() 
will "truncate" the whole database (very quickly), do not mix different 
caches in one database because of this!
- Do not use redis database numbers 0 and 1 in production, they are used 
and flushed (!) when running the unit tests.

How to test / use:
phpredis:
git clone https://github.com/owlient/phpredis.git
cd phpredis
phpize
./configure
make
make install
# Load redis php extension (for debian GNU/Linux):
echo 'extension="redis.so"' >> /etc/php5/conf.d/redis.ini
# Restart webserver ...

redis:
download redis 2.0.x (stable), or (head/master):
git clone https://github.com/antirez/redis.git
cd src
make
make install
./redis-server

# Sample configuration in localconf.php for redis as cache backend for 
pages cache with enabled caching framework:
$TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['cache_pages'] 
= array(
     'frontend' => 't3lib_cache_frontend_StringFrontend',
     'backend' => 't3lib_cache_backend_RedisBackend',
     'options' => array(
         'database' => 2,
     ),
);

Regards
Christian

[1] http://code.google.com/p/redis/
[2] https://github.com/owlient/phpredis
[3] http://forge.typo3.org/issues/9017