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Informations about the package magento-redis-session
Cm_RedisSession
A Redis-based session handler for Magento with optimistic locking.
Features:
- Falls back to mysql handler if it can't connect to Redis. Mysql handler falls back to file handler.
- When a session's data size exceeds the compression threshold the session data will be compressed.
- Compression libraries supported are 'gzip', 'lzf', 'lz4', and 'snappy'. -- Gzip is the slowest but offers the best compression ratios. -- Lzf can be installed easily via PECL. -- Lz4 is supported by HHVM.
- Compression can be enabled, disabled, or reconfigured on the fly with no loss of session data.
- Expiration is handled by Redis; no garbage collection needed.
- Logs when sessions are not written due to not having or losing their lock.
- Limits the number of concurrent lock requests before a 503 error is returned.
- Detects inactive waiting processes to prevent false-positives in concurrency throttling.
- Detects crashed processes to prevent session deadlocks (Linux only).
- Gives shorter session lifetimes to bots and crawlers to reduce wasted resources.
- Locking can be disabled entirely using config or
define('CM_REDISSESSION_LOCKING_ENABLED', FALSE);
or by setting$this->setFlag('', Cm_RedisSession_Model_Session::FLAG_READ_ONLY, 1)
flag in controller predispatch. - Requires PHP >= 5.3. Yes, this is a feature. You're welcome. ;)
Locking Algorithm Properties:
- Only one process may get a write lock on a session.
- A process may lose it's lock if another process breaks it, in which case the session will not be written.
- The lock may be broken after
BREAK_AFTER
seconds and the process that gets the lock is indeterminate. - Only
MAX_CONCURRENCY
processes may be waiting for a lock for the same session or else a 503 error is returned.
Session Cookie Management:
The Cookie Lifetime is configured here (Magento default): System > Configuration > Web > Session Cookie Management > Cookie Lifetime.
You can override the default session lifetime settings of this module by setting the <max_lifetime>
and <min_lifetime>
handle if you need to adjust your session lifetime settings.
Be aware that if the <max_lifetime>
setting is below your Cookie Lifetime, the <max_lifetime>
-setting will be taken.
Installation
This extension can be installed with either Composer or modman.
Important: The 3.0.0 release is packaged exclusively as a composer module and cannot be installed with modman. If you do not use composer stick with the 2.x release.
The Magento Compiler feature is currently not supported.
Modman Installation
-
Install module using modman:
modman clone https://github.com/colinmollenhour/Cm_RedisSession
If you want to install a specific version, you can add
-- --branch x.y.z
to the command. - Configure via app/etc/local.xml adding a
global/redis_session
section with the appropriate configuration if needed. See the "Configuration Example" below. - Refresh the config cache to allow the module to be installed by Magento.
-
Test the configuration by running the migrateSessions.php script in
--test
mode.sudo php .modman/Cm_RedisSession/migrateSessions.php --test
- Change the
global/session_save
configuration to "db" in app/etc/local.xml. The "db" value is the MySQL handler, but Cm_RedisSession overrides it to avoid modifying core files. - Migrate the old sessions to Redis. See the "Migration" section below for details. The migration script will clear the config cache after migration is complete to activate the config change made in step 5.
Configuration Example
Migration
A script is included to make session migration from files storage to Redis with minimal downtime very easy. Use a shell script like this for step 6 of the "Installation" section.
Depending on your server setup this may require some changes. Old sessions are not deleted so you can run it again
if there are problems. The migrateSessions.php script has a --test
mode which you definitely should use before
the final migration. Also, the --test
mode can be used to compare compression performance and ratios. Last but
not least, the --test
mode will tell you roughly how much space your compressed sessions will consume so you know
roughly how to configure maxmemory
if needed. All sessions have an expiration so volatile-lru
or allkeys-lru
are both good maxmemory-policy
settings.
Compression
Session data compresses very well so using compression is a great way to increase your capacity without
dedicating a ton of RAM to Redis and reducing network utilization.
The default compression threshold
is 2048 bytes so any session data equal to or larger than this size
will be compressed with the chosen compression_lib
which is gzip
by default. Compression can be disabled by setting the compression_lib
to none
. However, both lzf
and
snappy
offer much faster compression with comparable compression ratios so I definitely recommend using
one of these if you have root. lzf is easy to install via pecl:
sudo pecl install lzf
NOTE: If using suhosin with session data encryption enabled (default is suhosin.session.encrypt=on
), two things:
- You will probably get very poor compression ratios.
- Lzf fails to compress the encrypted data in my experience. No idea why...
If any compression lib fails to compress the session data an error will be logged in system.log
and the
session will still be saved without compression. If you have suhosin.session.encrypt=on
I would either
recommend disabling it (unless you are on a shared host since Magento does it's own session validation already)
or disable compression or at least don't use lzf with encryption enabled.
Bot Detection
Bots and crawlers typically do not use cookies which means you may be storing thousands of sessions that serve no purpose. Even worse, an attacker could use your limited session storage against you by flooding your backend, thereby causing your legitimate sessions to get evicted. However, you don't want to misidentify a user as a bot and kill their session unintentionally. This module uses both a regex as well as a counter on the number of writes against the session to determine the session lifetime.
Using with Cm_Cache_Backend_Redis
Using Cm_RedisSession alongside Cm_Cache_Backend_Redis should be no problem at all. The main thing to keep in mind is that if both the cache and the sessions are using the same database, flushing the cache backend would also flush the sessions! So, don't use the same 'db' number for both if running only one instance of Redis. However, using a separate Redis instance for each is recommended to make sure that one or the other can't run wild consuming space and cause evictions for the other. For example, configure two instances each with 100M maxmemory rather than one instance with 200M maxmemory.
License
@copyright Copyright (c) 2013 Colin Mollenhour (http://colin.mollenhour.com)
This project is licensed under the "New BSD" license (see source).