PHP-从MySQL获取数据的令人困惑的性能问题 [英] PHP - Confusing Performance Issue getting data from MySQL

问题描述

使用PHP/MySQLi，我想将一些数据提取到数组中.数据大小为几兆字节:

获取此数据的表转储的代码如下:

error_reporting(E_ALL);

 $q =  "SELECT * FROM mytable";
 if (!$result = $mysqli->query($q)) {
      echo "Error: Our query failed to execute and here is why: \n";
      echo "Query: " . $query . "\n";
      echo "Errno: " . $mysqli->errno . "\n";
      echo "Error: " . $mysqli->error . "\n";
      return $ret;
    }
if ($result->num_rows === 0) {
   $ret = 0;
   return $ret;
  }

$ret = array();
while($row = $result->fetch_array()){
  array_push($ret, $row);
} 

echo  mb_strlen(serialize((array)$ret), '8bit');

执行以下代码时，我得到了:

但是它说试图分配28672个字节，这远远超出了限制.为什么会这样?

解决方案

以这种方式思考.

您有100美元.您去糖果店，决定一次买200个$ 1糖果棒(您的while循环).

前100次购买将要进行，但是下次您尝试购买1美元的直板糖果时，会被告知您尝试花费1美元，但您已经花费了100美元". /p>

PHP正在报告您的 last 指令尝试使用的内存量.在这种情况下，可能是array_push($ret, $row);调用.

Using PHP/MySQLi I wanted to extract some data to an array. The data is a few megabytes in size:

The code to get the table dump of this data follows:

error_reporting(E_ALL);

 $q =  "SELECT * FROM mytable";
 if (!$result = $mysqli->query($q)) {
      echo "Error: Our query failed to execute and here is why: \n";
      echo "Query: " . $query . "\n";
      echo "Errno: " . $mysqli->errno . "\n";
      echo "Error: " . $mysqli->error . "\n";
      return $ret;
    }
if ($result->num_rows === 0) {
   $ret = 0;
   return $ret;
  }

$ret = array();
while($row = $result->fetch_array()){
  array_push($ret, $row);
} 

echo  mb_strlen(serialize((array)$ret), '8bit');

When executing the following code I got:

But it said tried to allocate 28672 bytes which is nowhere near the limit. Why is this?

解决方案

Think of it this way.

You've got $100. You go to the candy store, and decide to buy 200 $1 candy bars, one-by-one (your while loop).

The first 100 purchases are going to go through, but the next time you try buying a $1 candy bar, you're going to get told "you tried to spend a dollar, but you've already spent $100".

PHP is reporting the amount of memory your last instruction attempted to use. In this case, it's probably the array_push($ret, $row); call.

这篇关于PHP-从MySQL获取数据的令人困惑的性能问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！