Can I use memcached selectively?

Question

How does memcached really work?

If I have 5 different Percona MySQL databases d1, d2..d5, each serving a different PHP application a1, a2..a5 respectively, then can I just try to boost d1 with memcached?

I understand that memcached changes a lot and that in order to use it, I'll have to "tweak" the application that wants to use it.

So if I install memcached, without making relevant changes to a1, a2..a5, will that render the apps useless?

Or can I just make the modification to a1 only and then memcached affects d1 only and a2, a3...a5 can keep living their lives as normal?

In other words, does memcached, in any way affect how databases are accessed?

Answer 1

The only thing that memcached does is store and retrieve values in memory. That's it. It doesn't do anything on its own, either with databases or otherwise — if your applications are not currently written to make use of memcached, it will do absolutely nothing.

That being said, if you modify some of your applications to make use of memcached, it'll work just fine with them, and it won't affect any others.