Detailed explanations and examples of various methods for reading large files in PHP

This article mainly introduces in detail the various methods of reading large files in PHP. Interested friends can refer to it

Reading large files has always been a headache. We use PHP to Developing to read small files can be implemented directly using various functions. However, once you get to a large article, you will find that the commonly used methods cannot be used normally or take too long and are stuck. Let's take a look at the problem of reading large files in PHP. Solution, I hope the example can help you.

In PHP, when reading files, the fastest way is to use some functions such as file and file_get_contents. It can be completed beautifully with just a few lines of code. The functionality we need. But when the file being operated is a relatively large file, these functions may be insufficient. The following will start with a requirement to explain the commonly used operating methods for reading large files.

Requirements:
There is an 800M log file with about 5 million lines. Use PHP to return the contents of the last few lines.

Implementation method:

1. Directly use the file function to operate
Since the file function reads all the contents into the memory at one time, PHP in order to prevent some poorly written programs Occupying too much memory will cause insufficient system memory and cause the server to crash. Therefore, by default, the maximum memory usage is limited to 16M. This is set through memory_limit = 16M in php.ini. If this value is set to -1 , the memory usage is unlimited.

The following is a piece of code that uses file to extract the last line of this file:

<?php
　　ini_set(&#39;memory_limit&#39;, &#39;-1&#39;);
　　$file = &#39;access.log&#39;;
　　$data = file($file);
　　$line = $data[count($data) - 1];
　　echo $line;
?>

The entire code execution takes 116.9613 (s) .
My machine has 2 G of memory. When I press F5 to run, the system turns gray and recovers after almost 20 minutes. It can be seen that the consequences of reading such a large file directly into the memory are serious, so As a last resort, memory_limit cannot be set too high, otherwise you will have to call the computer room to reset the machine.

2. Directly call the Linux tail command to display the last few lines
Under the Linux command line, you can directly use tail -n 10 access.log to easily display the last few lines of the log file. You can directly Use PHP to call the tail command and execute the PHP code as follows:

<?php
  $file = &#39;access.log&#39;;
  $file = escapeshellarg($file); // 对命令行参数进行安全转义
  $line = `tail -n 1 $file`;
  echo $line;
?>

The entire code execution takes 0.0034 (s)

3. Directly Use PHP's fseek to perform file operations
This method is the most common method. It does not need to read all the contents of the file, but operates directly through pointers, so the efficiency is quite efficient. When using fseek to operate files, there are many different methods, and the efficiency may be slightly different. The following are two commonly used methods:

Method 1
First find the file through fseek The last EOF, then find the starting position of the last row, get the data of this row, then find the starting position of the next row, then take the position of this row, and so on, until the $num row is found.
The implementation code is as follows

<?php
$fp = fopen($file, "r");
$line = 10;
$pos = -2;
$t = " ";
$data = "";
while ($line > 0)
{
 while ($t != "＼n")
 {
 fseek($fp, $pos, SEEK_END);
 $t = fgetc($fp);
 $pos--;
 }
 $t = " ";
 $data .= fgets($fp);
 $line--;
}
fclose($fp);
echo $data
?>

The entire code execution takes 0.0095 (s)

Method 2
Still using fseek The method starts reading from the end of the file, but this time it is not reading bit by bit, but reading piece by piece. Every time a piece of data is read, the read data is placed in a buf, and then the newline character (\ n) to determine whether the last $num rows of data have been read.
The implementation code is as follows

<?php
$fp = fopen($file, "r");
$num = 10;
$chunk = 4096;
$fs = sprintf("%u", filesize($file));
$max = (intval($fs) == PHP_INT_MAX) ? PHP_INT_MAX : filesize($file);
for ($len = 0; $len < $max; $len += $chunk)
{
 $seekSize = ($max - $len > $chunk) ? $chunk : $max - $len;
 fseek($fp, ($len + $seekSize) * -1, SEEK_END);
 $readData = fread($fp, $seekSize) . $readData;
 if (substr_count($readData, "＼n") >= $num + 1)
 {
 preg_match("!(.*?＼n){" . ($num) . "}$!", $readData, $match);
 $data = $match[0];
 break;
 }
}
fclose($fp);
echo $data;
?>

The entire code execution takes 0.0009(s).

Method 3

<?php
function tail($fp, $n, $base = 5)
{
 assert($n > 0);
 $pos = $n + 1;
 $lines = array();
 while (count($lines) <= $n)
 {
 try
 {
  fseek($fp, -$pos, SEEK_END);
 }
 catch (Exception $e)
 {
  fseek(0);
  break;
 }
 $pos *= $base;
 while (!feof($fp))
 {
  array_unshift($lines, fgets($fp));
 }
 }
 return array_slice($lines, 0, $n);
}
var_dump(tail(fopen("access.log", "r+"), 10));
?>

The entire code execution takes 0.0003(s)

Method 4, PHP’s stream_get_line function , fast reading, it takes about 20 seconds to read a large file with 500,000 data! The example code is as follows

$fp = fopen('./iis.log', 'r'); //文件 
while (!feof($fp)) { 
 //for($j=1;$j<=1000;$j++) {     //读取下面的1000行并存储到数组中 
 $logarray[] = stream_get_line($fp, 65535, "＼n"); 
    // break;
 // } 
 
 }

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's learning.

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