PHP Read large file implementation Method _php tutorial

This article to introduce you to the students in PHP read large file implementation of the method, there is a need to understand the students can enter reference.

The requirements are as follows: an existing log file of about 1G, about more than 5 million lines, with PHP to return the last few lines of content.

Implementation method:

1. Use the file function directly to manipulate
Note: Because the file function reads everything into memory at once, and PHP prevents some poorly written programs from taking up too much memory and causing the server to go down, the limit is limited to 16M of memory by default, which is through php.ini Memory_ Limit = 16M To set, this value if set-1, the memory makes the usage unrestricted.

The following is a piece of code that uses file to remove the last line of the document.
The entire code execution takes time 116.9613 (s).

The code is as follows	Copy Code
Ini_set (' Memory_limit ', '-1 '); $file = ' Access.log '; $data = file ($file); $line = $data [Count ($data)-1]; Echo $line;

My machine is 2 g of memory, when the press F5 run, the system directly gray, almost 20 minutes after the recovery, it can be seen so large files directly into memory, the consequences is how much serious, so not million can not, memory_limit this thing can not be adjusted too high, otherwise only call room, Let the reset machine out.

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

Under the Linux command line, you can directly use Tail-n access.log very easy to display the last few lines of the log file, you can directly use PHP to invoke the tail command, execute PHP code as follows.
Complete code Execution time 0.0034 (s)

The code is as follows	Copy Code
File = ' Access.log '; $file = Escapeshellarg ($file); To safely escape command-line arguments $line = ' tail-n 1 $file '; Echo $line;

3. Use PHP fseek directly for file operation

This method is the most common way, it does not need to read all the contents of the file into the memory, but directly through the pointer to operate, so efficiency is quite efficient. There are many different ways to use fseek to manipulate files, and the efficiency may also vary slightly, and here are two common approaches.
Method One:
First, find the last EOF of the file by fseek, then find the beginning of the last line, take this row of data, then find the starting position of the next line, then take the position of this line, and so on, until the $num line is found.
The implementation code is as follows

Complete code Execution time 0.0095 (s)

The code is as follows	Copy Code
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));

Method Two:

Or use fseek way from the end of the file to read, but this is not a single read, but a piece of reading, each read a piece of data, the data will be read in a buf, and then by the number of newline characters (n) to determine whether the last $num line of data has been read.
The implementation code is as follows
The entire code execution takes time 0.0009 (s).

The code is as follows	Copy Code
$fp = fopen ($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

Method Three:

Complete code Execution time 0.0003 (s)

The code is as follows

Copy Code

$fp = fopen ($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;

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