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Search is Hard

The title of this post is a direct quote from a Facebook engineer presenting at the SXSW panel Beyond Lamp. Search is a critical function of any site, but its gotten much much harder as Google has gotten better. To quote the Beyond Lamp panel one more time:

Search is always compared against Google, which is like comparing the canoe

you just built to the QE2.

The difficulty of search is made apparent by the majority of sites, even major sites get it wrong. A large factor in the success of search is relevancy. Google takes into account 500 million variables in determining how relevant content is. Not only that, but they also know who you are, what you’ve clicked, and can make decisions based on that to present pages that are more relevant to you. Facebook’s EdgeRank, LinkedIn’s Signal are other examples of search implementations that are vast in scale.

In a startup, where time is of the essence and resources need to be begged, borrowed or stolen, search is a huge challenge. Like trying to be build the QE2 with nothing but a swiss army knife. Basic tools normally don’t cut it. MySQL’s FULLTEXT indexes are helpful, but start trying to implement basic IR techniques like booleans, and MySQL’s builtin functionality starts to lack the ability to get the results your want.

There are ways to simplify building search. Sphinx provides great matching capabilities and incredibly fast sorting. When combined with other data, Sphinx can be a great way to get users fast, meaningful results. The one downside with using a document based search engine is that there is little room for returning completely tailored results. Unlike MySQL, which allows you to slice and dice data in any way you choose, it is more difficult to return results that take into account relationship specific to users and documents. However, for most search tasks, it should function very well.

Published Oct 9, 2010

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