Donncha or whoever is listening, I have a few questions. I am running a multisite, multi-database WordPress Network with hundreds of blogs on a MediaTemple DV server (a VPS with 512mb RAM, PHP 5, on CentOS 5). I have successfully installed WP Super Cache and Memcached (and its associated PHP extension and WordPress plugin).
Upon studying the uses of Memcached and similar tools, I successfully installed APC. My reasoning: let Memcached foot the object caching, and let APC foot the opcode caching.
I'm going to think out loud here for a second, and then I'll get to my questions:
Memcached is useful because it excels in multiserver setups, which is where you need to balance server load in a distributed environment and avoid unnecessarily duplicating cached objects across the server network.
But APC, while it can do object caching, can't distribute caching across more than one server -- that's APC's "weakness". But APC's strength: in single-server setups, it is demonstrably quicker than Memcached in object caching. Additionally, APC provides *opcode caching*.
Now for my questions:
Can APC opcode caching improve the speed of the WordPress backend?
If so, does it begin to do so automatically once it is installed and enabled in PHP as an extension, or does APC need to be called from a WordPress plugin in order to opcode cache WordPress' PHP?
For single-server WordPress multisite installations, am I better off getting rid of Memcached and relying on APC both for opcode caching *and* object caching, and thus keep it all to one process? If so, is WP Super Cache able to make the most of APC, supposing I have an APC WordPress plugin, as it does with Memcached and it's associated WordPress plugin?
My network has a team of web designers building sites on it. Currently, they are all using a single Super Admin user login for all their activity. As far as you know, would I see any increase in speed in the WordPress backend if I have each web designer create and use his/her own Super Admin user, rather than this practice of having a single user entity performing multiple simultaneous activities?
As we speak, Memcached and APC are coexisting on my single-server setup, but I'm still pushing the limits of available RAM due to server load from my WordPress backend, so I'm really trying to figure out the best way to pimp this server short of upgrading to more RAM. My frontend is fast enough; it's my backend where I'm seeing all my server load issues.