MDEV-35806: Error in read_log_event() corrupts relay log writer, cras… #3745
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…hes server In Log_event::read_log_event(), don't use IO_CACHE::error of the relay log's IO_CACHE to signal an error back to the caller. When reading the active relay log, this flag is also being used by the IO thread, and setting it can randomly cause the IO thread to wrongly detect IO error on writing and permanently disable the relay log. This was seen sporadically in test case rpl.rpl_from_mysql80. The read error set by the SQL thread in the IO_CACHE would be interpreted as a write error by the IO thread, which would cause it to throw a fatal error and close the relay log. And this would later cause CHANGE MASTER to try to purge a closed relay log, resulting in nullptr crash. SQL thread is not able to parse an event read from the relay log. This can happen like here when replicating unknown events from a MySQL master, potentially also for other reasons. Also fix a mistake in my_b_flush_io_cache() introduced back in 2001 (fa09f2c) where my_b_flush_io_cache() could wrongly return an error set in IO_CACHE::error, even if the flush operation itself succeeded. Also fix another sporadic failure in rpl.rpl_from_mysql80 where the outout of MASTER_POS_WAIT() depended on timing of SQL and IO thread. Reviewed-by: Monty <[email protected]> Reviewed-by: Andrei Elkin <[email protected]> Signed-off-by: Kristian Nielsen <[email protected]>
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MDEV-35806: Error in read_log_event() corrupts relay log writer, crashes server
In Log_event::read_log_event(), don't use IO_CACHE::error of the relay log's
IO_CACHE to signal an error back to the caller. When reading the active
relay log, this flag is also being used by the IO thread, and setting it can
randomly cause the IO thread to wrongly detect IO error on writing and
permanently disable the relay log.
This was seen sporadically in test case rpl.rpl_from_mysql80. The read
error set by the SQL thread in the IO_CACHE would be interpreted as a
write error by the IO thread, which would cause it to throw a fatal
error and close the relay log. And this would later cause CHANGE
MASTER to try to purge a closed relay log, resulting in nullptr crash.
Also fix another sporadic failure in rpl.rpl_from_mysql80 where the outout
of MASTER_POS_WAIT() depended on timing of SQL and IO thread.