[_ck_]

Because of mysql replication, using the mysql cache is probably impossible on wp.com

Once you move beyond a single mysql server, things get complicated fast.

But that’s specifically the environment memcache was written for, not single server systems.

(by the way, how large is the wp.com memcache pool? I bet it’s massive)

However I find the MySQL cache has not been turned on for many VPS/dedicated servers. That’s a performance showstopper and makes a huge difference when the same queries are being done over and over on a typical bbPress install. A PHP opcode cache is the next largest performance improvement.

Here is the typical breakdown for MySQL vs Memcached performance:

Cache Type 	 Cache Gets/sec  (higher is better)

Array Cache  		365000              (this is local memory, fastest possible)

APC Cache 	 	98000                        (this is common memory via apc/eaccelertor/xcache)

File Cache  		27000                        (this is using the local disk cache)

Memcached Cache (TCP/IP) 	12200     <<<<====---

MySQL Query Cache (TCP/IP) 	 9900

MySQL Query Cache (Unix Socket)  13500    <<<<===---   (local mysql server, with cache)

Selecting from table (TCP/IP)	 5100             (remote mysql server, no cache)

Selecting from table (Unix Socket)  7400     (local mysql server, no cache)