Read replication with MySQL – part deux

Following up on my last post on read replication with MySQL, I read this post by Greg Linden on the subject of caching which mirrors my thinking on the matter (except that his is better written):

My opinion on this differs somewhat. I agree that read-only replication is at best a temporary scaling solution, but I disagree that object caches are the solution.

I think caching is way overdone, to the point that, in some designs, the caching layers sometimes contains more machines than the database layer. Caching layers add complexity to the design, latency on a cache miss, and inefficiency to use of cluster resources.

My experience at Feedster confirms this, once we got powerful enough servers for the DBMS, we found that we did not need to use memcached at all, in fact it was a hinderance more than anything because it added to the number of machines that needed to be administered.

As a small postscriptum, this post by Ronald Bradford does a very good job of listing out the reasons for replication along with the advantages and disadvantages of each.