Saving PHP session variables using multiple memcache servers

0
votes

I have been using memcache to store PHP sessions for years, love it. The performance is nice and it does not create thousands of files on disk.

I've got PHP 5.6 running on Debian.

Following the PHP session instructions, you need to add two add two entries to the php.ini file to get sessions stored in memcache. Something like this:

session.save_handler = memcache
session.save_path = "tcp://192.168.1.100:11211"

I've done that, been working great for years.

What I can't make work is defining multiple servers. The same PHP documentation page says you should be able to define multiple servers like this:

session.save_path = "tcp://192.168.1.100:11211,tcp://192.168.1.101:11211"

I believe when you define multiple servers, PHP is supposed to write the session data to each server - so you have redundancy. I want that redundancy.

My problem is as soon as I define multiple servers, PHP stops working and dumps an error like this:

session_start(): Failed to initialize storage module: memcache (path: tcp://192.168.1.100:11211,tcp:192.168.1.101:11211)

I can use either of the memcache servers individually with PHP, so I know they are both working, PHP can connect to both of them if defined individually. So what is PHP's issue when I define both?

1
phpsessionmemcachedredundancy

1 Answers

0
votes

You need to set session_redundancy for the Memcache PHP extension in memcache.ini.

The memcache.session_redundancy directive must be equal to the number of memcached servers + 1 for the session information to be replicated to all the servers. This is due to a bug in PHP.

See this post.