Is it recommended to store PHP Sessions in MemCache?

1. Yes, it is possible to keep PHP sessions in memcached.

The memcache extension even comes with a session handler that takes very little configuration to get up and running. http://php.net/manual/en/memcached.sessions.php

2. Memcache/Sticky Sessions

I don't really know which is "better". I feel this is going to be one of those "it depends" answers. It likely depends on your reasons for load balancing. If a small number of users cause lots of load each, or if it's a large number causing a small load each.

3. Cons of Memcache

There are probably 2 main cons to using memcache for sessions storage.

Firstly, it is volatile. This means, if one of your memcached instances is restarted/crashes etc. any sessions stored in that instance are lost. While if they were using traditional file based sessions, they will be still there when the server returns.

Secondly and probably more relevant, memcached doesn't guarantee persistance, it is only meant to be a cache. Data can be purged from memcached at any time, for any reason. While, in reality, the only reasons data should be purged is if the cache is nearing its size limits. The least recently accessed data will be expelled. Again, this might not be an issue, as the user is probably gone if their session is stale, but it depends on your needs.

1: YES. And I strongly recommend storing PHP sessions in Memcached. Here's why:

Memcached is great for storing small chunks of data that are frequently accessed by the database and filesystem.

Memcached was designed specifically for sessions. It was originally the brainchild of the lead developer of livejournal.com and later used to also cache the content of users' posts. The benefit was immediate: most of the action was taking place in memory. Page load times greatly improved.

Thankfully, PHP and Apache have an easy implementation to handle sessions with Memcached. Simply install with a few shell commands

example for Debian:

sudo apt-get -t stable install php7.4-memcached

and

change your php.ini settings to something similar to:

(taken from https://www.php.net/manual/en/memcached.sessions.php)

 session.save_handler = memcached
 ; change server:port to fit your needs...
 session.save_path = "localhost:11211"

The key is the session.save_path

It will no longer point to a relative file path on your server. APC was mentioned - APC for the caching of .php files used by the program. APC and Memcached will reduce IO significantly and leave Apache/Nginx free to server resources, such as images, faster.

2: No

3: The fundamental disadvantage of using Memcached is data volatility

Session data is not persistent in Memcached. So if and when the server crashes, all data in memory is lost. Everyone will have to log in again.

And then you have memory consumption...

Remember: the sessions are stored in the memory. If your website handles a large number of concurrent users, you may have to shell out a little extra money for a larger memory allocation.