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slow query optimization

Discussion in 'XenForo Development Discussions' started by Marcus, Aug 12, 2013.

  1. Marcus

    Marcus Well-Known Member

    I have a query that INNER JOINs both xf_post on post_id and xf_thread on thread_id.

    SELECT table.*, xf_post.post_id is 3x faster than SELECT table.*, xf_thread.title

    Do you have any idea why that could be possible? The same is for xf_post.* which is three times faster than xf_thread.*
  2. tyteen4a03

    tyteen4a03 Well-Known Member

    One is indexed while the other isn't...
  3. Marcus

    Marcus Well-Known Member

    I also thought so, but then it is just in the SELECT area, I am not querying for xf_thread.title.

    You are right, I changed the primary xf_thread index to thread_id & title, the query is now 3 times faster. Do you know why that is? So you should have an index also for the stuff you put in SELECT?
    Last edited: Aug 12, 2013
  4. tyteen4a03

    tyteen4a03 Well-Known Member

    No, don't just index everything - indexes are for locating a specific record quicker.

    If your query is performance-demanding, I suppose you can get the thread id first then separately get the thread title, but then I'm no performance guru.
  5. Marcus

    Marcus Well-Known Member

    The index helps 30% of my pages to display them 0.15 seconds faster. Guess that's worth it and I don't mind the larger index size. I have no idea, why a index on the thread title helps, as I only query thread_id against my other tables.
  6. xf_phantom

    xf_phantom Well-Known Member

    Reminds me of

    Marcus, MattW and tyteen4a03 like this.

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