#zend_cache

[stoeckl]

My MongoDB cache backend adapter for Zend Framework is on Gibhub

I just put my MongoDB cache backend adapter (for Zend Framework 1.11, not for ZF2!) on Github. It's a fork from Stunti (Olivier Bregeras) with some fixes and improvements, so Oliver did the hard work, not me!

You can find it here: Zend_Cache_Backend_Mongo

Details about Zend_Cache can be found here: Zend_Cache

MongoDB is very easy to install on Debian / Ubuntu, it's not more than a

apt-get install mongodb-server

to get the server running, listening (only) to localhost. DBs in MongoDB are created when they are requested, so you don't need to do anything apart from getting my cache backend running. :-)

I did some performance tests with it and compared to Memcache, here are my numbers:

Memcache

inserted 1000 items in 201ms (items/second: 4986) loaded 50000 random items in 5455ms (items/second: 9165) 1000 cache miss requests 109ms (items/second: 9153) Memory peak usage: 6029312 Byte (5.75 MB)

MongoDB

inserted 1000 items in 339ms (items/second: 2946) loaded 50000 random items in 5747ms (items/second: 8700) 1000 cache miss requests 115ms (items/second: 8660) Memory peak usage: 6029312 Byte (5.75 MB)

So MongoDB is a bit slower in writes and has almost the same read performance.

But the big advantage is that MongoDB supports tags which Memcache doesn't, so you can use the MongoDB backend adapter standalone (no two levels cache) with the full feature set (also the data is persistent in MongoDB) and almost the performace of Memcache. You can also use replication or even sharding on MongoDB, but you need to set this up for yourself.

Enjoy!

P.S.: Once I'll find the time I'll describe how MongoDB can do even better as a caching layer that caches your data as complex objects (including arrays) that supports atomic updates (even increments) without the need to read the data first.

[stoeckl]

Zend_Cache with backend adapter "file" can be Ouch!

Thx to the brilliant work some guy did ;-) to make Two Levels Cache work in Zend Framework I was able to find out how bad a Zend_Cache with the file backend adapter (used as the slow layer in our Two Level Cache) can be performance wise.

With the help of XHProf I was able to find out why some requests in our web application took several seconds (causing this error). Using a quite long cache timeout (24 hours or so) and having lots of cache items the cleanup which the file backend adapter has to do on each x'th request (configurable) was very heavy. It had to go through ten thousands of files to find the ones to remove (as they were timed out), which is something that needs some time.

I solved this problem by using a different cache backend adapter for the slow layer. The winner for this task is MongoDB with some code I found on Github to build a Zend_Cache_Backend_Mongo. I don't link to it as I had to do some changes to the original code. Will put my version on Github and drop another post here once this is done.

Conclusion is that using the file adapter for Zend_Cache only makes sense if you have a small number of cache items (maybe up to 1000 or 2000 is ok), otherwise you'll get into serious performance trouble sooner or later.