Re: [squid-users] Squid vs caching products like memcached

On 5/16/07, lightbulb432 <veerukrishnan@hotmail.com> wrote:

> What's the difference between the reverse proxying features of Squid and a
> caching product like memcached?

Memcached is a distributed, in memory, hash table with a network
interface. Most often you stuff the results of expensive queries
(database, computations, XML processing) into memcached so that
multiple nodes can get the data without having to do the expensive
query.

Squid as a reverse proxy caches http objects -- pages, css,
javascript, images, etc. You use squid to offload entire requests to
your web server.

As an example at b5media we front our web farm with Squid, but only
cache images, javascript, and CSS. WordPress and Squid don't play
well together because WordPress doesn't send out proper headers for
Squid to use, so we don't cache pages.

Beside taking hits off the web server, Squid is also good at spoon
feeding slow clients. Previously a slow client keeps an expensive
Apache slot tied up, now Squid takes that data from Apache and feeds
the client -- squid is more efficient at this task than Apache.

On the WordPress backend we store a lot of internal stuff in
memcached. We have some internal code that uses a REST API that
figures out what blog goes in which channel. Rather than make a
handful of REST calls on every page view, which incurs latency for the
web hit and CPU for the XML processing, we check memcached to see if
the PHP object exists. If we get a memcached cache hit we've just
saved ourselves a lot of time. If we get a miss, we make the API
calls and stuff the PHP object back into memcached for the next
person.

I look at the caching within a LAMP application as a multilevel thing.
 We cache the http objects we can with squid. If we have to generate
a page we cache what we can in memcached, just like we cache compiled
PHP scripts in an opcode cache. If we have to hit the database we use
MySQL query caching at that layer.

It's not a one-or-the-other type of thing, these are two tools that
are clearly the best at what they do, and can (should?) be used
together as part of a good architecture.

Sean

-- 
Sean Walberg <sean@ertw.com>    http://ertw.com/