Maybe we could even write a blog post on how to use Redis when using Piwik in a load balanced environment and also include QueuedTracking plugin for handling peaks etc. I will create an issue for this.

Maybe something like this? @mattab

How to configure Redis as a shared cache in a load balanced environment

By default Piwik caches data in the local filesystem of each server. If your Piwik environment consists of multiple servers a common problem is that caches are only invalidated on one server instead of all servers. To workaround this we recommend to use a shared cache for all of your servers. You can do this by installing and configuring Redis.

To use Redis as a cache follow these steps:

• Make sure you are using at least Piwik 2.10 (latest Piwik version recommended)
• Install Redis see Redis Quickstart
• Install the PHP extension phpredis
• Don't forget to restart your webserver
• Once successfully setup, enable it in the config file config/config.ini.php. Make sure to adjust the section [RedisCache] to your needs. You have to make this change on each of your server.

[Cache]
backend = chained

[ChainedCache]
backends[] = array
backends[] = redis

[RedisCache]
host = "127.0.0.1" 
port = 6379
timeout = 0.0
password = ""
database = 14
; In case you are using queued tracking: Make sure to configure a different database! Otherwise queued requests will be flushed

How to configure Redis for session handling in a load balanced environment

By default Piwik uses the filesystem as a session handler. If your Piwik environment consists of multiple servers a common problem is that multiple sessions are created per user meaning a user might have to log in multiple times and a log out might actually log out a user only on one server. To workaround this there are two options:

• Use the database to handle sessions
• Use Redis to handle sessions (described in this FAQ). Redis is usually faster than a database and we recommend it in case one has Redis already configured as a [Cache](TODO LINK TO REDIS CACHE FAQ) or for Queued Tracking.

To use Redis as a session handler follow these steps:

• Install Redis see Redis Quickstart
• Install the PHP extension phpredis
• Configure Redis as PHP session handler in php.ini on each of your server:

session.save_handler = redis 
session.save_path    = tcp://127.0.0.1:6379?database=10
; In case you are using queued tracking or Redis as a cache: Make sure to configure a different database! Otherwise queued requests will be flushed

; multiple servers can be configured comma separated
session.save_path = "tcp://host1:6379?weight=1&database=2, tcp://host2:6379?weight=2&timeout=2.5, tcp://host3:6379?weight=2"

See Redis Session Handler for more documentation.

• Don't forget to restart your webserver
• Once successfully setup, make sure there is no Piwik default session handler configured by setting the session_save_handler to an empty value in the config file config/config.ini.php. You have to make this change on each of your server.

[General]
session_save_handler = ""

assigning to @mattab for now to put it into FAQ in case it is ok

Text is very clear, both FAQs have been published:

• How to configure Redis as a shared cache in a load balanced environment?
  • How do I configure Redis for session handling in a load balanced environment?

Nice new resource for admin who want to re-use the power of Redis!

“session.save_path = tcp://127.0.0.1:6379?database=10”invalid ，Excuse me where is the problem？