Why not let the fs handle this ??

[Evan Martin]

On 6/6/06, Constantin B <const at const.org> wrote:
> The purpose of this email is to ask what are the future limitations of my
> setup ? I mean for the moment it do the
> job , but where is the gotcha ?

1) Your caches can be up to 30 minutes out of date.  If you use
memcached like it's intended, updates to the backend clear the cache
so your cache will never be out of date.

2) Your caches are per-machine, so each machine has a duplicate copy
of the same data.  This is of course fine if you have enough RAM per
machine for each hold its own data, but large memcached installs have
multiple gigabytes of data in memcached.

3) Any disk-intensive operations on your servers (like backups) will
cause the OS to flush its buffer cache, making the next fetch from the
cache be very slow.  (See some recent threads on this list about this
problem.)

I'd say: it's nice that you're doing caching in general, and it
obviously helps, but memcached is for when the sort of design you've
made stops scaling.  See the front page of the memcached site for a
discussion of this.