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From:hezx Date:February 1 2008 4:24am
Subject:bk commit into 5.1 tree (hezx:1.2513) BUG#26489
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ChangeSet@stripped, 2008-02-01 12:24:43+08:00, hezx@stripped +1 -0
  BUG#26489 Corruption in relay logs
    
  Here is the scenario that causes the failure.(by Mats)
  
    1. The to-be corrupt log event (let's call it X), is split into two
       packets B and C on the network level (net_write_buff()). The parts
       are X = (x',x''). The part x' ends up in packet B and part x''
       ends up in packet C. Prior to the corrupt event X, the event Y has
       been written successfully, but has been split into two packets as
       well, which we call (y',y'').
    2. The master sends packet A = (y'',x') to the slave, increases the
       packet sequence number, the slave receives the packet, but fails
       to reply before the master gets a timeout.
    3. Since the master got a timeout, it reports failure, and aborts
       sending the binary log by exiting mysql_binlog_send(). However, it
       leaves the buffer intact, still holding y'' (but not x', since the
       write_pos is not increased).
    4. After exiting mysql_binlog_send(), the master does a
       disconnection of the client thread, which involves sending an
       error message e to the client (i.e., the slave).
    5. In this case, net_write_buff() is used again, but this time the
       old contents of the packet is used so that the new packet is
       D = (y'',e). Note that this will use a new packet sequence number,
       since the packet number was increased in step 2.
    6. The slave receives the tail y'' of the Y log event, concatenates
       this with x' (which it already received), and writes the event
       (x',y'') it to the relay log since it hasn't noticed anything is
       amiss.
    7. It then tries to read more bytes, which is either e (if the length
       given for X just happened to match the length given for Y, or just
       plain garbage because the slave is out of sync with what is
       actually sent.
    8. After a while, the SQL thread tries to execute the event (x',y''),
       which is very likely to be just nonsense.
  
  The problem can be fixed by not resetting net->error after the call of 
  mysql_binlog_send, so the error message will not be sent and the connection
  will be closed.

  sql/sql_parse.cc@stripped, 2008-02-01 12:24:39+08:00, hezx@stripped +0 -1
    Do not reset net->error after call of mysql_binlog_send

diff -Nrup a/sql/sql_parse.cc b/sql/sql_parse.cc
--- a/sql/sql_parse.cc	2007-12-21 05:11:31 +08:00
+++ b/sql/sql_parse.cc	2008-02-01 12:24:39 +08:00
@@ -1310,7 +1310,6 @@ bool dispatch_command(enum enum_server_c
       unregister_slave(thd,1,1);
       /*  fake COM_QUIT -- if we get here, the thread needs to terminate */
       error = TRUE;
-      net->error = 0;
       break;
     }
 #endif
Thread
bk commit into 5.1 tree (hezx:1.2513) BUG#26489hezx1 Feb