Toru Maesaka

Something I’ve been wanting to add to libmemcached for a while is a cluster analysis feature that can be used to calculate useful information for system admins that deploy multiple memcached nodes. Many webshops already do this by writing their own so it makes sense to have this functionality in a community driven library. This means people can pitch in their useful stats calculation which results in benefiting everyone.

So, with that in mind I wrote a patch that contains the initial codebase for the analyzer which is now reviewed and merged into trunk. This also gave me a reason to claim the commit access that Brian has been offering me for nearly a year… (I know, I’m lazy and useless).

At the moment, you can get the following information with the new memcached_analyze(3) function:

• Average item size in the pool
• Node that is eating the most memory
• Node with least designated memory remaining
• Node with the longest uptime
• Pool-wide Hit Ratio

I know, there isn’t much at the moment but more will be added in upcoming pushes. The analyzer is pretty easy to extend so please feel free to throw patches for it! Or, you could pitch in by telling us useful figures that should be computed.

Hopefully this new feature will be released next month :)

Avoid the library by using memstat

The memstat tool (distributed with libmemcached) has been enhanced with the new ‘–analyze’ option that will use the analyzer and give you a human readable output. You should use memstat unless you need to explicitly use the values returned by the analyzer.

Using it is easy, all you need to do is specify the servers that you’d like to inspect and give it the ‘–analyze’ option like this (only two servers for demo purpose):

$ memstat --servers=localhost:11211,localhost:11311 --analyze
Memcached Cluster Analysis Report
 
    Number of Servers Analyzed         : 2
    Average Item Size (incl/overhead)  : 54 bytes
 
    Node with most memory consumption  : localhost:11211 (54 bytes)
    Node with least free space         : localhost:11211 (67108810 bytes remaining)
    Node with longest uptime           : localhost:11311 (780s)
    Pool-wide Hit Ratio                : 100%

Easy!

Toru Maesaka memcached, oss libmemcached, memcached