Re: [PATCH -RFC 0/2] mm/ext4: avoid data corruption when extending DIO write race with buffered read

Baokun Li
2023-12-07T06:41:09Z

On 2023/12/7 5:55, Theodore Ts'o wrote:
> On Tue, Dec 05, 2023 at 09:19:03PM +0800, Baokun Li wrote:
>> Thank you very much for your detailed explanation!
>> But the downstream users do have buffered reads to read the relay log
>> file, as I confirmed with bpftrace. Here's an introduction to turning on
>> relay logging, but I'm not sure if you can access this link:
>> https://blog.csdn.net/javaanddonet/article/details/112596148
> Well, if a mysql-supplied program is trying read the relay log using a
> buffered read, when it's being written using Direct I/O, that's a bug
> in mysql, and it should be reported as such to the mysql folks.
I was mistaken here, it now looks like reads and writes to the relay
log are buffered IO, and I'm still trying to locate the issue.
>
> It does look like there is a newer way of doing replication which
> doesn't rely on messign with log files. From:
>
> https://dev.mysql.com/doc/refman/8.0/en/replication.html
>
> MySQL 8.0 supports different methods of replication. The
> traditional method is based on replicating events from the
> source's binary log, and requires the log files and positions in
> them to be synchronized between source and replica. The newer
> method based on global transaction identifiers (GTIDs) is
> transactional and therefore does not require working with log
> files or positions within these files, which greatly simplifies
> many common replication tasks. Replication using GTIDs guarantees
> consistency between source and replica as long as all transactions
> committed on the source have also been applied on the replica. For
> more information about GTIDs and GTID-based replication in MySQL,
> see Section 17.1.3, “Replication with Global Transaction
> Identifiers”. For information on using binary log file position
> based replication, see Section 17.1, “Configuring Replication”.
>
> Perhaps you can try and see how mysql handles GTID-based replication
> using bpftrace?
>
> Cheers,
>
> - Ted
Thank you very much for your solution! I'll try it.

Thanks!
--
With Best Regards,
Baokun Li
.