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POMySQL multiple joins being slow
 

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  1. POMySQL multiple joins being slow
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    <p>I've got a table with the following structure:</p> <p><img src="https://i.stack.imgur.com/jyZEs.png" alt="db structure"></p> <p>I've got all my primary keys correct and every int &amp; date column has an index, and <code>(playerId, groupId)</code> in <code>player_groups</code> is an unique index. All tables are using InnoDB, and the relations you see are also references in InnoDB.</p> <p>Full database source, with data, roughly similar to the examples I'll demonstrate below: <a href="https://www.dropbox.com/s/kzf89occlq4legy/bf4_performance.sql" rel="nofollow noreferrer">https://www.dropbox.com/s/kzf89occlq4legy/bf4_performance.sql</a></p> <p>Queries:</p> <ul> <li><p>Query #1: <code>SELECT * FROM playerkills ORDER BY date DESC LIMIT 300;</code> </p></li> <li><p>Query #2: <code>SELECT p.playerName AS player, p2.playerName AS target, w.weaponName AS weapon, date, headshot, s.serverName AS server FROM playerkills JOIN players p ON playerkills.playerId = p.playerId JOIN players p2 ON playerkills.targetId = p2.playerId JOIN weapons w ON playerkills.weaponId = w.weaponId JOIN servers s ON playerkills.serverId = s.serverId ORDER BY date DESC LIMIT 300;</code></p></li> </ul> <p>Performance on my own machine, which has a lot of resources:</p> <ul> <li>Query #1: 0.0016 sec</li> <li>Query #2: 1.3050 sec</li> </ul> <p>Performance on the live database host, which has considerably less resources:</p> <ul> <li>Query #1: 0.046 sec</li> <li>Query #2: 1.297 sec</li> </ul> <p>I'm afraid something is highly impacting the performance as it works fine without any <code>JOIN</code> statements. Can anyone shed some more light on this?</p> <p>ps (<strong>edit</strong>). Also possibly important to add: This database is in live being updated every few seconds, so the results of the queries cannot be cached the same way as queries on static data could be.</p> <p><strong>EDIT 2:</strong> Profiling on the static version (on <code>localhost</code>) gave me this picture:</p> <p><img src="https://i.stack.imgur.com/w6gjR.png" alt="db profile"></p> <p>Output of <code>EXPLAIN</code>:</p> <p><img src="https://i.stack.imgur.com/y30PQ.png" alt="db explain"></p>
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    1. USskiwi
    1. USskiwi
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    1. COthe more tables you join the slower it gets, can improve via proper indexing but will not be as fast as single table select
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      1. USKonstantin
    2. CO@user2864740 Added the more detailed data per request.
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      1. USskiwi
    3. COYou are joining `p2` with `playerkills` on `targetId`, which does not have an index. This means that a full table scan have to be made. Try to add an index to `playerkills` and show the output of `EXPLAIN` again.
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      1. USMats Kindahl
 

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