Akom's Tech Ruminations

Various tech outbursts - code and solutions to practical problems

MySQL replication dies with fatal error 1236: Client requested master to start replication from impossible position

Posted by Admin • Friday, February 4. 2011 • Category: Linux

This time, my master-master setup stopped replicating with no explanation at all - running START SLAVE yielded no warnings or errors. Inspecting the log yielded the aforementioned error (on Ubuntu, mysql logs to /var/log/syslog by default):
[ERROR] Error reading packet from server: Client requested master to start replication from impossible position ( server_errno=1236) [ERROR] Got fatal error 1236: 'Client requested master to start replication from impossible position' from master when reading data from binary log [4654]: 110204 10:09:20 [Note] Slave I/O thread exiting, read up to log 'mysqld-bin.000742', position 4274

So at first I thought this was a weird bug or a stunnel issue, but looking at 'mysqld-bin.000742' on the master it turns out that it's only 3980 bytes - position 4274 is indeed impossible. But how did it get this way?


Without being able to "just resume and let it fix itself" I will need to CHANGE MASTER myself, but to what position?

  1. Let's see what happened in that binlog file - it's not very large: (See syntax) . Runing this on the MASTER
    SHOW BINLOG EVENTS in 'mysqld-bin.000742' from 0;
  2. I have a bunch of INSERT's in there, so I check the slave to see if that data exists - and I have everything to the very last statement.
  3. So I pull up the next binlog, carefully:
    SHOW BINLOG EVENTS in 'mysqld-bin.000743' from 0 limit 10;
  4. The very first INSERT's data doesn't exist, nor the next, so I will assume that I should start from the beginning of this binlog file. Perhaps there was a power outage on the master and the previous file got cut off earlier than the slave expected - not really sure.


  1. Change the slave to read from a different position (see MySQL Change Master Syntax): Running this on the SLAVE
  2. And away it goes!

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