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POEfficiently querying a 15,000,000 rows table in MySQL
 

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    <p>Consider the following database tables:</p> <ul> <li>Table "messages" with 13,000,000 rows (one row per message).</li> <li>Table "users" with 3,000,000 rows (one row per user).</li> </ul> <p>The following query is used to fetch a bunch of messages and the corresponding users:</p> <pre><code>SELECT messages.id, messages.message, users.id, users.username FROM messages INNER JOIN users ON messages.user_id=users.id WHERE messages.id in (?, ?, ?, ? ... a total of 100 "?":s); </code></pre> <p>100 messages are fetched in each query. </p> <p>"messages" is indexed on id (primary key, BIGINT <em>not</em> auto-generated) and user_id.</p> <p>"users" is indexed on id (primary key, INT auto-generated).</p> <p>The database is MySQL using MyISAM.</p> <p>Currently the query takes well over 3000 ms to execute which puzzles me since "messages" is indexed on "id", so retrieving the correct rows should be very quick.</p> <p>My question is: Given the describe scenario and setup, is a 3000 ms query time "normal" or am I missing something? Please let me know if further details are required.</p> <p><b>Update #1:</b> Here are the table definitions:</p> <pre><code>CREATE TABLE messages ( id bigint(20) NOT NULL DEFAULT '0', user_id int(11) NOT NULL DEFAULT '0', message varchar(160) NOT NULL DEFAULT '', PRIMARY KEY (id), KEY user_id (user_id), ) ENGINE=MyISAM DEFAULT CHARSET=utf8; CREATE TABLE users ( id int(11) NOT NULL DEFAULT '0', username varchar(32) NOT NULL DEFAULT '', PRIMARY KEY (id), UNIQUE KEY username (username), ) ENGINE=MyISAM DEFAULT CHARSET=utf8; </code></pre> <p>The only "non-standard" thing I observe in the definitions is that "messages.id" is a BIGINT rather than an INT. Could that be a hint?</p>
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    1. COCan you post the output of EXPLAIN SELECT ...
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    2. COHave you tried putting the 100 MessageIds in a temp table, and doing a Join to that table, or an Exists?
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    3. COIs messages.user_id indexed?
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