PHP: examples of quick reading of large files

Source: Internet
Author: User
Tags memory usage php code

In PHP, the quickest way to read files is to use functions such as file and file_get_contents, A few simple lines of code can perfectly complete the functions we need. However, when the operated file is a relatively large file, these functions may not be able to work properly. The following describes how to read large files from a requirement, common operation methods.

Requirement

There is a more than 5 million MB log file with about lines. Use PHP to return the last few lines of content.

Implementation method

1. Directly use the file function.

The file function reads all the content into the memory at a time. To prevent some poorly written programs from occupying too much memory, PHP causes insufficient system memory and server downtime, therefore, the maximum memory usage is 16 MB by default. set memory_limit = 16 M in ini. If this value is set to-1, the memory usage is not limited.

Below is a piece of code that uses file to retrieve the last line of the file:

The code is as follows: Copy code
<? Php
Ini_set ('memory _ limit ','-1 ');
$ File = 'Access. Log ';
$ Data = file ($ file );
$ Line = $ data [count ($ data)-1];
Echo $ line;
?>

It takes 116.9613 seconds to complete the code execution ).

My machine has 2 GB of memory. When I press F5 to run the machine, the system will be grayed out directly, and it will be restored after about 20 minutes. It can be seen that all such large files will be directly read into the memory, the consequence is serious, so no more than. memory_limit cannot be too high. Otherwise, you only need to call the data center to let the reset machine go.

2. Directly call the Linux tail command to display the last few lines

In 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:

The code is as follows: Copy code
<? Php
$ File = 'Access. Log ';
$ File = escapeshellarg ($ file); // escape command line parameters safely
$ Line = 'tail-n 1 $ file ';
Echo $ line;
?>

It takes 0.0034 seconds to complete the code execution)

3. Directly use PHP fseek for file operations

This method is the most common method. It does not need to read all the content of the file, but directly uses pointers for operations, so the efficiency is quite efficient. When using fseek to operate files, there are also a variety of different methods, and the efficiency may be slightly different. Below are two common methods:

Method 1

First, find the last EOF the file through fseek, then find the starting position of the last row, get the data of this row, find the starting position of the next row, and then take the location of this row, and so on until the $ num row is found.

# The implementation code is as follows:

The code is as follows: Copy code
<? 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
?>

It takes 0.0095 seconds to complete the code execution)

Method 2

The fseek method is used to read the last part of the file, but it is not a one-bit read, but a one-piece read. When each piece of data is read, put the read data in a buf, and then determine whether the last $ num row data has been read by changing the number of linefeeds (\ n.

# The implementation code is as follows:

The code is as follows: Copy code
<? 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;
?>

It takes 0.0009 seconds to complete the code execution ).

Method 3

The code is as follows: Copy code

<? 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 ));
?>

It takes 0.0003 seconds to complete the code execution)

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