19.5.5 How to Report Replication Bugs or Problems

When you have determined that there is no user error involved, and replication still either does not work at all or is unstable, it is time to send us a bug report. We need to obtain as much information as possible from you to be able to track down the bug. Please spend some time and effort in preparing a good bug report.

If you have a repeatable test case that demonstrates the bug, please enter it into our bugs database using the instructions given in Section 1.5, “How to Report Bugs or Problems”. If you have a “phantom” problem (one that you cannot duplicate at will), use the following procedure:

1. Verify that no user error is involved. For example, if you update the replica outside of the replication threads, the data goes out of synchrony, and you can have unique key violations on updates. In this case, the replication thread stops and waits for you to clean up the tables manually to bring them into synchrony. This is not a replication problem. It is a problem of outside interference causing replication to fail.

2. Ensure that the replica is running with binary logging enabled (the log_bin system variable), and with the --log-slave-updates option enabled, which causes the replica to log the updates that it receives from the source into its own binary logs. These settings are the defaults.

3. Save all evidence before resetting the replication state. If we have no information or only sketchy information, it becomes difficult or impossible for us to track down the problem. The evidence you should collect is:

   • All binary log files from the source

   • All binary log files from the replica

   • The output of SHOW MASTER STATUS from the source at the time you discovered the problem

   • The output of SHOW REPLICA STATUS from the replica at the time you discovered the problem

   • Error logs from the source and the replica

4. Use mysqlbinlog to examine the binary logs. The following should be helpful to find the problem statement. log_file and log_pos are the Master_Log_File and Read_Master_Log_Pos values from SHOW REPLICA STATUS.

   $> mysqlbinlog --start-position=log_pos log_file | head

After you have collected the evidence for the problem, try to isolate it as a separate test case first. Then enter the problem with as much information as possible into our bugs database using the instructions at Section 1.5, “How to Report Bugs or Problems”.