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copied!<h2>The golden rule</h2> <p>The number one thing to do when you encounter (or expect to encounter) memory pressure is: <strong>do not read massive amounts of data in memory at once if you intend to process them sequentially</strong>.</p> <p>Examples:</p> <ul> <li>Do not fetch a large result set in memory as an array; instead, fetch each row in turn and process it before fetching the next</li> <li>Do not read large text files in memory (e.g. with <code>file</code>); instead, read one line at a time</li> </ul> <p>This is not always the most convenient thing in PHP (arrays don't cut it, and there is <em>a lot</em> of code that only works on arrays), but in recent versions and especially after the introduction of <a href="http://php.net/manual/en/language.generators.overview.php" rel="noreferrer">generators</a> it's easier than ever to stream your data instead of chunking it.</p> <p>Following this practice religiously will "automatically" take care of other things for you as well:</p> <ul> <li>There is no longer any need to clean up resources with a big memory footprint by closing them and losing all references to them on purpose, because there will be no such resources to begin with</li> <li>There is no longer a need to unset large variables after you are done with them, because there will be no such variables as well</li> </ul> <h2>Other things to do</h2> <ul> <li>Be careful of creating closures inside loops; this should be easy to do, as creating such inside loops is a bad code smell. You can always lift the closure upwards and give it more parameters.</li> <li>When expecting massive input, design your program and pick algorithms accordingly. For example, you can mergesort any amount of text files of any size using a constant amount of memory.</li> </ul>

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