Difference between Memcache, APC, XCache and other alternatives I've not heard of

At work, we've recently started designing an application to me "large scale" (we're engineering for th开发者_开发知识库e potential to serve up many millions of hits a day). One of the senior devs and the sysadmin have set up memcache on the server.

As I understand it, Memcache will hold query results and certain tables in memory for X amount of time and keep everything hunky dory.

A drawback of memcache it seems is that I just can't for the life of me manage to set it up on my local dev environment. I've followed a few different instructionals on how to compile it for yourself. Most, if not all of the steps seem to work properly but get this error on PHPLoad:

 [11-Sep-2010 16:02:30] PHP Warning:  PHP Startup: Unable to load dynamic library '/Applications/MAMP/bin/php5.3/lib/php/extensions/no-debug-non-zts-20090626/memcached.so' - dlopen(/Applications/MAMP/bin/php5.3/lib/php/extensions/no-debug-non-zts-20090626/memcached.so, 9): image not found in Unknown on line 0  

Not the primary question but incedentally, if you've been able to compile Memcache for MAMP 1.9 on Snow Leopard, please let me know the trick.

My primary question is about what the differences are between the various web caching technologies. I've seen mention of Memcache, APC and Xcache (here: Cache results of a mysql query manually to a txt file) but don't know the pros, cons and differences between each.

To my mind, Memcache has the advantage of being the one that the project's lead dev and our sysadmin chose. It has the disadvantage of being utter foobar to try and set up and compile on a Mac. :-^)

Anyone who I'd love to hear from anyone who can enumerate the pros and cons of each (or even one of) the other cachine technologies. Where are they best used, how are they best used. And so on.

It's all useful information I think.

Thanks so much for lending your time to expanding my knowledge. - Alex.

First, a list of opcode cachers for php.

Second Memcache/MemcacheD is not an Opcode Cacher. It is a distributed memory caching system. It does not improve the speed/performance of your PHP code. It can be used to store data only.

APC, EAccelerator, XCache and the others are non distributed, meaning you can only store data on the local web-server. However all of these are opcode cachers and can improve the performance of your PHP app. Most, excluding EAccelerator (in the current version) can also store data.

I generally choose APC for the opcode cacher (It reportedly will be included into the core of PHP 6). However if I also have more than one web-server for the site I will also make use of MemcacheD.

Edit 1 I agree it is very annoying to setup APC, Memcache on MAMP. There are however tutorials out there dealing with such.

Edit 2 Also with regards to the best Opcode Cacher for your app really depends on which server you are using. Some work better on some systems. It also depends on the size and scale of your app as to how the cachers perform.

Edit 3 Very interesting article here about comparing performance of a few different cachers. (This article appears to be written in 2006 and should not really be used for current reference)

APC is a opcode cache. It will store parsed PHP code so that every time your PHP files do not need to get parsed.

Memcache is a data cache. It will store data as a key value pair.