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copied!<p>From <a href="http://dev.mysql.com/doc/refman/5.1/en/server-status-variables.html" rel="nofollow noreferrer"><strong>documentation</strong></a>:</p> <blockquote> <p><code>Handler_read_rnd</code></p> <p>The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that don't use keys properly.</p> <p><code>Handler_read_rnd_next</code></p> <p>The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.</p> </blockquote> <p><code>read_rnd*</code> means reading actual table rows with a fullscan.</p> <p>Note that it will show nothing if there is a index scan combined with a row lookup, it still counts as key read.</p> <p>For the schema like this:</p> <pre><code>CREATE TABLE mytable (id INT NOT NULL PRIMARY KEY, data VARCHAR(50) NOT NULL) INSERT INTO mytable VALUES … SELECT id FROM mytable WHERE id BETWEEN 100 AND 200 SELECT * FROM mytable WHERE id BETWEEN 100 AND 200 </code></pre> <p>, the latter two queries will both return <code>1</code> in <code>read_key</code>, <code>101</code> in <code>read_next</code> and <code>0</code> in both <code>read_rnd</code> and <code>read_rnd_next</code>, despite the fact that actual row lookups occur in the second query.</p>

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