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Statistics and Postgres - How the planner sees your data.

Nathan Boley presents: Statistics and Postgres - How the planner sees your data. Postgres relies heavily on statistics collected from data tables to execute queries in the most efficient way possible. Despite the relative simplicity of these statistics, the actual process by which they are collected and used to generate plans is a bit enigmatic. In the next 50 minutes, I will go through the assumptions that the planner makes about data access patterns, the heuristics that generate and apply the summary statistics, and a theorem from probability theory that is central to the planner's estimates. Finally, if time permits, I will show how a custom selectivity function can dramatically improve the planner accuracy for odd data distributions. My hope is that a clear understanding of the process by which Postgres collects and applies statistics will remove some of the black magic from tuning Postgres and spur the development of better analysis techniques. This meeting will also be streamed live on the web at Remote people can ask questions there or in Pizza from The Cheeseboard contributed by Continuent. RSVP to get a slice!

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  • githogori

    We need more meetings like this one. There was no need to ask "where's the beef?"!

    September 11, 2009

  • Brian H.

    Speaker is well into the subject.. and the subject is core infrastructure.. but the talk itself rambled.. So I say "good"

    September 10, 2009

  • Jay J.

    Pretty advanced, but I think I almost understood it.

    September 9, 2009

  • CB

    Good presentation, got some new insight into how PG comes up with query plans. But -- had hoped to learn how to influence the planner, and we didn't really get into that very much.

    September 9, 2009

  • Samuel V.

    The potential was there but it was hard to follow the main thread of this talk, if there was one. Several points were covered but unless you're stewing in this stuff all of the time, it didn't necessarily make sense to someone who had a more general interest. This is not uncommon; many people giving talks could do a better job in preparing and delivering them.

    September 9, 2009

  • Jonathan P.

    Failure to arrange for a projector caused waste of time and impaired communication. Content presupposed more knowledge than I had, so most of the talk didn't help me. I expected the speaker to draw conclusions about how a user of PostgreSQL can diagnose and improve its performance, but I found almost no such advice in the talk. I learned that custom data types should be equipped with equality and less-than operators (something I don't expect to relate to me), but not much else in the "here's what you can do" category.

    September 9, 2009

  • Ragi B.

    Insightful and interesting!

    September 9, 2009

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