Data Disappearing

Anon

I am having a problem with one of my scripts. Currently I use fopen, fwrite, and fclose statements to write large amounts of data into one file on my server (MySQL is currently not an option). It works fine for a while, but then when I go back to check the data something happens and where in the information should be is either a or nothing at all.

This does not happen all through the file, but instead in just certain areas. I've tried everything I can think of to preserve the data file, but with the amount of people that use it (about a couple thousand a day who take the data, explode there personal data, implode the data, and then write it back to the file) it works for a while and then all of a such the data is gone.

To cut down on some interference I tried CHMODing the file to 777, 755, 606, and 6, but none of which seem to help.

Is there another statement I can use that won't cause this problem other than fwrite, or am I doomed to have to fix the data repeatedly? I have enough backups running through the data that I don't lose any, but it is a hassle to have to repair the file constantly.

Thank you for any help you can be.

Anon

Are these couple thousand users reading and writing from the same file, or from individual files? If the former, no wonder you're having problems! Check ont the file locking function flock(). Yes, it will slow down your throughput, but there is no alternative to letting multiple users safely update a text file.

Anon

They're using the same file since in the past I had problems using multiple files. I'm currently running the scripts with flock's in them, and so far it seems fine, but is there any other things that I can do that may prevent the problems if this doesn't work.

Anon

If you're using flock() already, the only obvious possibility is that one or more scripts isn't using it correctly.

The correct sequence, assuming you're going to update the files, and ignoring most error checking:

if (! ($fd = fopen( $filename, "r+")))
  $fd = fopen( $filename, "w+"); // first-time creation of file
flock( $fd, 2 );
// do whatever you want with the file here...
flock( $fd, 3 ); //others are now free to update the file
// other stuff here...
fclose( $fd );

You can omit the flock( , 3) if you just close the file immediately after updating it.

Anon

Thanks, so far flock() seems to be working great.