In auto-commit mode, updating both trx and non-trx tables (i.e. issuing a mixed
statement) causes the following sequence of events:
1 - "Flush trx changes" (MYSQL_BIN_LOG::write) - T1:
1.1 - mutex_lock (&LOCK_log)
1.2 - mutex_lock (&LOCK_prep_xids)
1.3 - increase prepared_xids
1.4 - mutex_unlock (&LOCK_prep_xids)
1.5 - mutex_unlock (&LOCK_log)
2 - "Flush non-trx changes" (MYSQL_BIN_LOG::write) - T1:
2.1 - mutex_lock (&LOCK_log)
2.2 - mutex_unlock (&LOCK_log)
3. "unlog" - T1
3.1 - mutex_lock (&LOCK_prep_xids)
3.2 - decrease prepared xids
3.3 - pthread_cond_signal(&COND_prep_xids);
3.4 - mutex_unlock (&LOCK_prep_xids)
The "FLUSH logs" command produces the following sequence of events:
1 - "FLUSH logs" command (MYSQL_BIN_LOG::new_file_impl) - user thread:
1.1 - mutex_lock (&LOCK_log)
1.2 - mutex_lock (&LOCK_prep_xids)
1.3 - while (prepared_xids) pthread_cond_wait(..., &LOCK_prep_xids);
1.4 - mutex_unlock (&LOCK_prep_xids)
1.5 - mutex_unlock (&LOCK_log)
A deadlock will arise if T1 flushes the trx changes and thus increases
prepared_xids but before it is able to continue the execution and flush the
non-trx changes, an user thread calls the "FLUSH logs" command and wait that
the prepared_xids is decreased and gets to zero. However, T1 cannot proceed
with the call to "Flush non-trx changes" because it will block in the mutex
"LOCK_log" and by consequence cannot complete the execution and call the
unlog to decrease the prepared_xids.
To fix the problem, we ensure that the non-trx changes are always flushed
before the trx changes.
Note that if you call "Flush non-trx changes" and a concurrent "FLUSH logs" is
issued, the "Flush non-trx changes" may block, but a deadlock will never happen
because the prepared_xids will eventually get to zero. Bottom line, there will
not be any transaction able to increase the prepared_xids because they will
block in the mutex "LOCK_log" (MYSQL_BIN_LOG::write) and those that increased
the prepared_xids will eventually commit and decrease the prepared_xids.
mysql-test/extra/binlog_tests/binlog_failure_mixing_engines.test:
Merged the test case into rpl_mixing_engines.test.
mysql-test/extra/rpl_tests/rpl_mixing_engines.inc:
Incorporated some tests from binlog_failure_mixing_engines.test and
fixed after BUG#47323.
mysql-test/extra/rpl_tests/rpl_mixing_engines.test:
Incorporated some tests from binlog_failure_mixing_engines.test and
fixed after BUG#47323.
mysql-test/suite/binlog/r/binlog_mixed_failure_mixing_engines.result:
Merged the test case into rpl_mixing_engines.test.
mysql-test/suite/binlog/r/binlog_row_failure_mixing_engines.result:
Merged the test case into rpl_mixing_engines.test.
mysql-test/suite/binlog/t/binlog_mixed_failure_mixing_engines.test:
Merged the test case into rpl_mixing_engines.test.
mysql-test/suite/binlog/t/binlog_row_failure_mixing_engines.test:
Merged the test case into rpl_mixing_engines.test.
mysql-test/suite/rpl/r/rpl_mixed_mixing_engines.result:
Incorporated some tests from binlog_failure_mixing_engines.test and
changed after BUG#47323.
mysql-test/suite/rpl/r/rpl_row_mixing_engines.result:
Incorporated some tests from binlog_failure_mixing_engines.test and
changed after BUG#47323.
mysql-test/suite/rpl/r/rpl_stm_mixing_engines.result:
Incorporated some tests from binlog_failure_mixing_engines.test and
changed after BUG#47323.
Non-transactional updates that take place inside a transaction present problems
for logging because they are visible to other clients before the transaction
is committed, and they are not rolled back even if the transaction is rolled
back. It is not always possible to log correctly in statement format when both
transactional and non-transactional tables are used in the same transaction.
In the current patch, we ensure that such scenario is completely safe under the
ROW and MIXED modes.
