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LinkedIn Search: A Look Beneath the Hood

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Last week, I had the good fortune to attend a presentation by John Wang, search architect at LinkedIn. You may have read my earlier posts about LinkedIn introducing faceted search and celebrating the interface from a user perspective. John’s presentation at the SDForum took a developer’s perspective, discussing the challenges of combining faceted search and social networking at scale.

John was kind enough to publish his slides, and I’ve embedded them above. Unfortunately, there’s no recording of the extensive Q&A (which included various attempts to get John to reveal the precise details of LinkedIn’s data volume), but the slides are quite meaty.

Personally, I learned two surprising things from the talk.

First, I was surprised that LinkedIn dismisses index/cache warming as “cheating”, instead computing almost everything in real time. Specifically, I would have expected LinkedIn to cache information like a user’s set of degree-two connections: these are expensive to compute at query time, especially when the social graph is distributed and sharded by user. I did ask John whether LinkedIn recomputes a user’s degree-two network during a session, and he admitted that LinkedIn is sensible enough to “cheat” and not perform this expensive but almost useless re-computation.

Second, I learned about reference search, a feature I may have missed because it is only available for premium LinkedIn accounts. It’s a nice feature, allowing you to search against company + date range pairs. People who are familiar with implementing faceted search may recognize the preservation of such associations between facet values as a gnarly implementation challenge.

All in all, it was a treat to get this look under the hood, as well as to finally meet John in person. I also ran into Gene Golovchinsky there–so much for my spending a few days on the west coast incognito!

In any case, I’m looking forward to seeing Gene, some of John’s colleagues, and many more interesting people at the Search and Social Media Workshop (SSM 2010) on Wednesday. My apologies to those who aren’t able to attend this oversubscribed event. I promise to blog about it!


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