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POWhy are certain types of prepared queries using PDO in PHP with MySQL slow?
 

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  1. POWhy are certain types of prepared queries using PDO in PHP with MySQL slow?
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    <p>When using <code>SELECT * FROM table WHERE Id IN ( .. )</code> queries with more than 10000 keys using PDO with prepare()/execute(), the performance degrades ~10X more than doing the same query using mysqli with prepared statements or PDO without using prepared statements. </p> <p>More strange details:</p> <ul> <li><p>More typical SELECT statements that don't have the <code>WHERE Id IN( ..)</code> clause perform fine even with 100K+ rows. <code>SELECT * FROM table WHERE Id</code> for example is fast. </p></li> <li><p>The performance degradation occurs after prepare()/execute() is complete - it's entirely in <code>PDOStatement::fetch()</code> or <code>PDOStatement::fetchAll()</code>. The MySQL query execution time is tiny in all cases - this isn't a case of a MySQL optimization.</p></li> <li><p>Splitting the 10K query into 10 queries with 1K keys is performant.</p></li> <li><p>Using mysql, mysqli with prepared statements, or PDO without prepared statements is performant.</p></li> <li><p>PDO w/prepared takes ~6 seconds on the example below, while the others take ~0.5s.</p></li> <li><p>It gets worse in a non-linear fashion the more keys you have. Try 100K keys.</p></li> </ul> <p>Sample code:</p> <pre><code>// $imageIds is an array with 10K keys $keyCount = count($imageIds); $keys = implode(', ', array_fill(0, $keyCount, '?')); $query = "SELECT * FROM images WHERE ImageID IN ({$keys})"; $stmt = $dbh-&gt;prepare($query); $stmt-&gt;execute($imageIds); // until now, it's been fast. fetch() is the slow part while ($row = $stmt-&gt;fetch()) { $rows[] = $row; } </code></pre>
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    1. USDon MacAskill
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      1. POWhy are certain types of prepared queries using PDO in PHP with MySQL slow?
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    1. COIf this is reproducible, then you probably would need to profile PHP to see why the slowdown occurs.
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      1. USMatthew
    2. COTry `PDO::ATTR_EMULATE_PREPARES` or disabling `PDO::MYSQL_ATTR_USE_BUFFERED_QUERY`. And note that libmysql and mysqlnd backends behave differently.
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      1. POWhy are certain types of prepared queries using PDO in PHP with MySQL slow?
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    3. COTried both of those already, no major impact. mysql, mysqli, and PDO are all using mysqlnd.
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      1. USDon MacAskill
 

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