Posts by: Lorenzo Alberton

• Profiling with XHProf December 1, 2009

  If there’s something we developers are really bad at, it’s guessing. We think we know which parts of our application are slow, and spend a lot of time optimising those, but in reality the bottlenecks are often somewhere else. The only sane thing to do is measuring, with the help of some profiling tools.

  There are a few profilers available for PHP, the most commonly used being Xdebug, which combined with KCacheGrind/WinCacheGrind/MacCallGrind can show the function call graph and the time spent in each function.

  In this article, we’re going to try another profiler, XHProf, developed at Facebook and open sourced in March 2009 (under the Apache 2.0 license). XHProf is a function-level hierarchical profiler, with a PHP extension (written in C) to collect the raw data, and a few PHP scripts for the reporting/UI layer.

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• Graphs in the database: SQL meets social networks September 7, 2009

  Graphs are ubiquitous. Social or P2P networks, thesauri, route planning systems, recommendation systems, collaborative filtering, even the World Wide Web itself is ultimately a graph! Given their importance, it’s surely worth spending some time in studying some algorithms and models to represent and work with them effectively. In this short article, we’re going to see how we can store a graph in a DBMS. Given how much attention my talk about storing a tree data structure in the db received, it’s probably going to be interesting to many. Unfortunately, the Tree models/techniques do not apply to generic graphs, so let’s discover how we can deal with them.

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