Homo-Adminus Blog

We were using memcache in our application for a long time and it helped a lot to reduce DB servers load on some huge queries. But there was a problem (sometimes called a “dog-pile effect”) - when some cached value was expired and we had a huge traffic, sometimes too many threads in our application were trying to calculate new value to cache it.

For example, if you have some simple but really bad query like

which could be really slow on a huge tables, and your cache expires, then ALL your clients calling a page with this counter will end up waiting for this counter to be updated. Sometimes there could be tens or even hundreds of such a queries running on your DB killing your server and breaking an entire application (number of application instances is constant, but more and more instances are locked waiting for a counter).

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How often do we think about our http sessions implementation? I mean, do you know, how your currently used sessions-related code will behave when sessions number in your database will grow up to millions (or, even, hundreds of millions) of records? This is one of the things we do not think about. But if you’ll think about it, you’ll notice, that 99% of your session-related operations are read-only and 99% of your sessions writes are not needed. Almost all your sessions table records have the same information: session_id and serialized empty session in the data field.

Looking at this sessions-related situation we have created really simple (and, at the same time, really useful for large Rails projects) plugin, which replaces ActiveRecord-based session store and makes sessions much more effective. Below you can find some information about implementation details and decisions we’ve made in this plugin, but if you just want to try it, then check out our project site.

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Because of not fully correct testing methodology, benchmark results are not fully correct. So, I decided to redo all tests. New benchmark results you can get in “Looking For Optimal Solution” series Summary post.

This week we have started one new project with Ruby on Rails as primary framework. My first task was to prepare runtime environment for it on one of our development servers. When I have tried to research how people doing it, I noted that there is no information about how to deploy rails application with nginx as frontend and what is performance of such solution. Before blindly make any decisions about future platform I’ve decided to make some performance tests of the some most popular rails web servers/frontends. Results of these tests you can find here with configuration samples for all software that I have used.

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