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    <blockquote> <p>When I assign the results of the second query to <code>$results</code>, what happens to the memory associated with the previous results?</p> </blockquote> <p>When you execute this:</p> <pre><code>$results = $db-&gt;query($query); </code></pre> <p>If there was something in <code>$results</code> before, this old content cannot be accessed anymore, as there is no reference left to it.</p> <p>In such a case, PHP will mark the old content of the variable as "<em>not needed anymore</em>" -- and it will be removed from memory when PHP needs some memory.</p> <p>This, at least, is true for general PHP variables; in the case of results from an SQL query, though, some data may be kept in memory on the driver-level -- over which PHP doesn't have much control.</p> <p><br></p> <blockquote> <p>Should I be freeing that result before assigning the new one?</p> </blockquote> <p>I never do that -- but, quoting the manual page of <a href="http://fr2.php.net/manual/en/mysqli-result.free.php" rel="noreferrer"><code>mysqli_result::free</code></a>:</p> <blockquote> <p>Note: You should always free your result with mysqli_free_result(), when your result object is not needed anymore</p> </blockquote> <p>It probably doesn't matter for a small script... And the only way to be sure would be to test, using <a href="http://fr2.php.net/memory_get_usage" rel="noreferrer"><code>memory_get_usage</code></a> before and after calling that method, to see whether there is a difference or not.</p> <p><br></p> <blockquote> <p>Related to 1, when I do clean up at the end, is cleaning up just the last results enough?</p> </blockquote> <p>When the scripts end:</p> <ul> <li>The connection to the database will be closed -- which means any memory that might be used by the driver should be freed</li> <li>All variables used by the PHP script will be destroyed -- which means the memory they were using should be freed.</li> </ul> <p>So, at the end of the script, there is probably really no need to free the resultset.</p> <p><br></p> <blockquote> <p>When I do try to clean up a result, should I be freeing it as above, should I be closing it, or both?</p> </blockquote> <p>If you close the connection to the database <em>(using <a href="http://fr2.php.net/manual/en/mysqli.close.php" rel="noreferrer"><code>mysqli::close</code></a> like you proposed)</em>, this will disconnect you from the database.</p> <p>Which means you'll have to re-connect if you want to do another query! Which is not good at all <em>(takes some time, resources, ... )</em></p> <p>Generally speaking, I would not close the connection to the database until I am really sure that I won't need it anymore -- which means I would not disconnect before the end of the script.</p> <p>And as "<em>end of the script</em>" means "<em>the connection will be closed</em>" even if you don't specify it; I almost never close the connection myself.</p>
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    1. POMySQLi query results: Best approach, do you close, free, both?
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    1. USPeter Mortensen
    1. USPascal MARTIN
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    1. COWow! That's an excellent and very well written and informative answer. Exactly what I was looking for. Thanks! I guess all in all I am being overly concerned for a language that handles garbage collection. Thanks again!
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      1. USCarvell Fenton
    2. COYou're welcome :-) ;;; well, you may be true about garbage collection -- but don't also forget that PHP's primary use is for scripts that rarely last more than a couple of seconds -- which means even if there is some memory leak, it generally isn't that bad.
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    3. COGood point. I am still a "fledgling" in the world of web development, so perhaps my past of using older compiled languages has me disproportionately apprehensive when it comes to memory management! :)
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