#26490 [Com]: Lost connection to MySQL server during query

[Ryan dot Springer at billingconcepts dot com]

 ID:               26490
 Comment by:       Ryan dot Springer at billingconcepts dot com
 Reported By:      chris dot noden at monstermob dot com
 Status:           Verified
 Bug Type:         MySQL related
 Operating System: *
 PHP Version:      4CVS, 5CVS (2004-03-13)
 New Comment:

Is everyone who is effected by this bug running Red Hat?  If so, this
may be a libc problem.  See:

http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=75128


Previous Comments:
------------------------------------------------------------------------

[2004-03-11 11:39:40] [EMAIL PROTECTED]

This happens on the following versions:

 php 4.3.3, 4.3.4, 4.3.5RC3

 with bundled or external mysql client code
 with shared or buildin

 MySQL Server Version here is 4.0.18

 The MySQL Log shows this row on a 'connection lost' error:
 Aborted connection 2048 to db: [....] (Got an error reading
communication packets)



------------------------------------------------------------------------

[2004-03-11 11:35:27] [EMAIL PROTECTED]

Since i just stumbled across the very same problem, i wrote a small (?)
testcode to check it.

It seems like using pconnect in favor of a 'normal' connect fixes the
problem for the testcode, while it does not for my reallife
application.

The code assumes a database with at least 100 rows.
Structure as follows:

CREATE TABLE debug2 (
  ID int(11) NOT NULL auto_increment,
  CODE varchar(10) NOT NULL default '',
  PRIMARY KEY  (ID),
) TYPE=MyISAM 


This is the testcode, run it from cli ;)

<?php

        function do_something($ppid,$data) {

                $db=mysql_connect('db.local.dev','dev','dev');
                echo mysql_error();

                mysql_selectdb('fpostv4',$db);
                echo mysql_error();

                foreach ($data as $row) {
                        $sql="update debug2 set CODE='1' where ID='{$row['ID']}'";
                        echo "[$ppid] $sql\n";
                        $rc=mysql_query($sql);
                        echo mysql_error();
                }

        }

 $db=mysql_connect('db.local.dev','dev','dev');
 mysql_selectdb('fpostv4',$db);
 echo mysql_error();

 $rc=mysql_query('update debug2 set code=""');
 echo mysql_error();

 $rc=mysql_query('select * from debug2');
 echo mysql_error();

 for ($t=0; $t<10; $t++) {

         $pid = pcntl_fork();
         if ( $pid == -1 ) {
                         die('Error during fork() - halting');
         } elseif ( $pid == 0 ) {
                         $ppid=getmypid();
                         mysql_data_seek($rc,$t*10);
                         echo mysql_error();

                         for ($x=0; $x<10; $x++) {
                                 $data[]=mysql_fetch_assoc($rc);
                         }
                         do_something($ppid,$data);
                         die();
         } else {
                         $pidlist[]=$pid;
                         $sendPos += $perThread;
         }

 }

         // wait for them to finish...
         while (count($pidlist)) {
                 foreach ($pidlist as $key => $ppid) {
                         $tmp=pcntl_waitpid($ppid, $temp, WNOHANG);
                         if ($tmp!=0 ) {
                                unset($pidlist[$key]);
                         }
                 }
                 sleep(2);
         }


 ?>


You may have to run the code multiple times to actually see the
problem. The "Lost connection" error doesn't occur on a fixed rate or
value. You may be 'lucky' and don't hit it at all in a run..

Feel free to contact me in irc ( freenode / ircnet ) 


------------------------------------------------------------------------

[2003-12-01 13:16:29] chris dot noden at monstermob dot com

Description:
------------
MySQL version 4.0.13 running on a different server on the LAN using
pconnect:

After using a pcntl_fork() the child thread suffers from the "2013 :
Lost connection to MySQL server" error above.

I can continue to use the MySQL connection without connecting again
implying that the connection has miraculously re-established itself!

The error can occur at any stage in a query, (eg during submission or
reading the results of the query).

The error usually manifests itself when the query returns no results. 
The error comes from the parent process!!

I have tried all sorts of workarounds, to no avail.

Reproduce code:
---------------
do {
        $sql = "SELECT stuff FROM db WHERE a=b";
        $qryID = mysql_query($sql,$Link_ID
        while (mysql_fetch_array($qryID)) {
                // Fork off a child
                $is_parent = pcntl_fork();
                if ($is_parent > 0) {
                        // I am the child - do some stuff
                        exit;
                } else {
                        // I am the parent do some stuff
                } // end if/else
                
                sleep(1);
} while (condition);    


Expected result:
----------------
Normal database flow.

Actual result:
--------------
Error 2013 - Lost connection to MySQL server during query


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