MySQL Bugs: #6148: STOP/START SLAVE IO_THREAD gives relay log event parse error

Bug #6148	STOP/START SLAVE IO_THREAD gives relay log event parse error
Submitted:	18 Oct 2004 20:17	Modified:	25 Nov 2004 14:16
Reporter:	Mikael Fridh	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Replication	Severity:	S2 (Serious)
Version:	4.0.21	OS:	Linux (Linux, any?)
Assigned to:	Mats Kindahl	CPU Architecture:	Any

Description:
When you start and stop the IO_THREAD the slave will stop replicating with the error:

Could not parse relay log event entry. The possible reasons are: the master's binary log is corrupted (you can check this by running 'mysqlbinlog' on the binary log), the slave's relay log is corrupted (you can check this by running 'mysqlbinlog' on the relay log), a network problem, or a bug in the master's or slave's MySQL code. If you want to check the master's binary log or slave's relay log, you will be able to know their names by issuing 'SHOW SLAVE STATUS' on this slave.

Typing STOP SLAVE; followed by START SLAVE; let's replication start again as if nothing happened.

How to repeat:
1. Set up a replicating slave.
2. STOP SLAVE IO_THREAD
3. START SLAVE IO_THREAD

To get replication going again:
STOP SLAVE
START SLAVE

A sample mysql session of a recreation of the bug

Attachment: mysql_session_log.txt (text/plain), 3.90 KiB.

Worth noting: It _has_ been working in older versions!

From what I am testing now, something indeed looks fishy.

Mikael,
could you please post here the complete error message, I mean including the lines just before "could not parse etc" ?
I was able to get a "could not parse" but it does not mean it's the same problem as yours.
Thanks!

Another question: what was the latest version you had it work fine, please?

For the work of my colleagues, here is a test case (just copy it into mysql-test/t/ into 4.0).
source include/master-slave.inc;
connection slave;
stop slave;
create table t1(n int);
let $1=5000;
disable_query_log;
while ($1)
{
 eval insert into t1 values($1);
 dec $1;
}
enable_query_log;
save_master_pos;

connection slave;
start slave;
sleep 1;
stop slave io_thread;
start slave io_thread;
sync_with_master;

connection master;
drop table t1;
save_master_pos;
connection slave;
sync_with_master;

If you run a debug binary you should get an assertion failure in slave.cc (this will be printed in mysql-test/var/log/slave.err). If you run a non-debug binary you'll get a message in var/log/slave.err saying "could not parse relay log entry" as our user posted here.

Guilhem, a quick guess would be that it worked in 4.0.15.