这是我使用的代码：
if(mt_rand(0,20000)==0)
{
$lines = file($fileName);
if (count($lines)>50000)
{
$lines=array_slice($lines, -50000, 50000, true);
}
$result=implode("'n",lines);
file_put_contents($fileName, $result . "'n",FILE_APPEND);
}
我经常遇到这样的错误：
[25-Nov-2013 23:20:40 UTC] PHP Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 33 bytes) in /home/datetrng/public_html/checkblocked.php on line 40
[26-Nov-2013 02:41:54 UTC] PHP Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 27 bytes) in /home/datetrng/public_html/checkblocked.php on line 40
[26-Nov-2013 09:56:49 UTC] PHP Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 72 bytes) in /home/datetrng/public_html/checkblocked.php on line 40
[26-Nov-2013 12:44:32 UTC] PHP Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 2097152 bytes) in /home/datetrng/public_html/checkblocked.php on line 40
[26-Nov-2013 13:53:31 UTC] PHP Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 2097152 bytes) in /home/datetrng/public_html/checkblocked.php on line 40
如果我们只想通过擦除文件的开头来缩短文件，我想阅读整个文件可能不是一个好主意。
知道其他选择吗？
fopen fwrite fseek可能会派上用场
我认为您只需要文件中的最后50000行。
if(mt_rand(0,20000)==0)
{
$tmp_file = $fileName . '.tmp';
$cmd = "tail -n 50000 $fileName > $tmp_file";
exec($cmd);
rename($tmp_file, $fileName);
}
纯php的更新
我制作了一个大约100000行的文件：
<?php
$file_name = 'tmp.dat';
$f = fopen($file_name, 'w');
for ($i = 0; $i < 1000000; $i++)
{
fwrite($f, str_pad($i, 100, 'x') . "'n");
}
fclose($f);
这个文件大约有970M
[huqiu@localhost home]$ ll -h tmp.dat
-rw-rw-r-- 1 huqiu huqiu 97M Nov 27 06:08 tmp.dat
读取最后50000行
<?php
$file_name = 'tmp.dat';
$remain_count = 50000;
$begin_time = microtime(true);
$temp_file_name = $file_name . '.tmp';
$fp = fopen($file_name, 'r');
$total_count = 0;
while(fgets($fp))
{
$total_count++;
}
echo 'total count: ' . $total_count . "'n";
if ($total_count > $remain_count)
{
$start = $total_count - $remain_count;
echo 'start: ' . $start . "'n";
$temp_fp = fopen($temp_file_name, 'w');
$index = 0;
rewind($fp);
while($line = fgets($fp))
{
$index++;
if ($index > $start)
{
fwrite($temp_fp, $line);
}
}
fclose($temp_fp);
}
fclose($fp);
echo 'time: ' . (microtime(true) - $begin_time), "'n";
rename($temp_file_name, $file_name);
经过时间：0.63908791542053
total count: 1000000
start: 950000
time: 0.63908791542053
结果：
[huqiu@localhost home]$ ll -h tmp.dat
-rw-rw-r-- 1 huqiu huqiu 4.9M Nov 27 06:23 tmp.dat
为什么不将fseek指针指向要消除的点之后的位置？使用fpassthru来节省一些内存可能也会更好。