[Linux-cluster] Some problems on using GFS

[PN]

Dear all,

We found some problems on using GFS. We are using RHEL 4U5 with CentOS 4U5
CSGFS RPMs.

Given the following PHP program (for testing):

<?php

  $input      = '/data08/test/src';
  $tmp_prefix = '/data08/test/tmp';
  $dest       = '/data08/test/dest';
  $hostname   = trim( shell_exec('hostname') );
  $pid        = posix_getpid();

  while ( true ) {

    $tmp = $tmp_prefix . '_' . microtime(true) . '_' . $hostname . '_' .
$pid;
    copy( $input, $tmp );

    $is_success = rename( $tmp, $dest );

    if ( ! $is_success ) {
      echo 'error' . "\n\n";
    }
  }

?>


The above program only do a simple task:

  Copy the file "src" to a tmp file, and then rename the tmp file to "dest".

where "/data08/test/" is a directory mounted on GFS.



When two or more instances of this program running concurrently in *different
nodes*, the rename operation was *failed*.
But there is *no problem* when two or more instance of this program running
concurrently in the *same node*.


*Example stderr when running the above program:*

  PHP Warning:
rename(/data08/proga15_test/20090204/tmp_1233720656.1111_mp-bla03_18274,/data08/proga15_test/20090204/dest):
No such file or directory in /data08.mount/proga15_test/20090204/t.php on
line 14
  error

  PHP Warning:
rename(/data08/proga15_test/20090204/tmp_1233720656.9956_mp-bla03_18274,/data08/proga15_test/20090204/dest):
No such file or directory in /data08.mount/proga15_test/20090204/t.php on
line 14
  error

  PHP Warning:
rename(/data08/proga15_test/20090204/tmp_1233720659.7083_mp-bla03_18274,/data08/proga15_test/20090204/dest):
No such file or directory in /data08.mount/proga15_test/20090204/t.php on
line 14
  error

  PHP Warning:
rename(/data08/proga15_test/20090204/tmp_1233720661.1308_mp-bla03_18274,/data08/proga15_test/20090204/dest):
No such file or directory in /data08.mount/proga15_test/20090204/t.php on
line 14
  error

  PHP Warning:
rename(/data08/proga15_test/20090204/tmp_1233720662.5406_mp-bla03_18274,/data08/proga15_test/20090204/dest):
No such file or directory in /data08.mount/proga15_test/20090204/t.php on
line 14
  error

  PHP Warning:
rename(/data08/proga15_test/20090204/tmp_1233720663.9784_mp-bla03_18274,/data08/proga15_test/20090204/dest):
No such file or directory in /data08.mount/proga15_test/20090204/t.php on
line 14
  error

  PHP Warning:
rename(/data08/proga15_test/20090204/tmp_1233720665.5586_mp-bla03_18274,/data08/proga15_test/20090204/dest):
No such file or directory in /data08.mount/proga15_test/20090204/t.php on
line 14
  error



Then we've added a while loop before rename.

  while ( true ) {

    $tmp = $tmp_prefix . '_' . microtime(true) . '_' . $hostname . '_' .
$pid;
    copy( $input, $tmp );

*       while (!file_exists($tmp)) {}*

    $is_success = rename( $tmp, $dest );

    if ( ! $is_success ) {
      echo 'error' . "\n\n";
    }
  }

The file really exists before rename. It does not generate an infinite loop
and the same error occurred.

Any suggestion or idea?  Thanks a lot.

Regards,
PN
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