Description:
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I am seeing an issue in PHP 5.6.17 where after running a large database query, calling mysqli_fetch_field increases memory usage by a large amount.  The same issue occurs in PHP 7.0.2.

In the below example, the call to fetch_field increases the memory usage from 1.8MB to 6.6MB.

I have placed SQL to create a test table of 100,000 rows at https://drive.google.com/uc?export=download&id=0B37DKbJklxg_Y3NadnRjc2tVbE0.

Is this expected behavior or an issue with memory usage?

Thanks for your help.


Test script:
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<?php
$mysqli = new mysqli('localhost', 'test', 'test', 'test');

$mysqli->real_query("SELECT * FROM a");

$result = $mysqli->store_result();

echo 'a: '.memory_get_usage()."\n";

$field = $result->fetch_field();

echo 'b: '.memory_get_usage()."\n";
exit;


Expected result:
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a: 1833136
b: 1833136 (or close to it)


Actual result:
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a: 1833136
b: 6635728