MySQL Forums
Forum List  »  InnoDB

Re: Failed to start mysql due to start_lsn and ens_lsn issue
Posted by: Jakub Lopuszanski
Date: August 11, 2022 04:29AM

After internal discussion with InnoDB, and some code analysis, I'm forced to reach the (a priori improbable) conclusion that your hardware+OS+LVM+lib combination doesn't properly handle fsync().
This is really serious and dangerous circumstance, but not something I can help fixing.

The https://serverfault.com/questions/279571/lvm-dangers-and-caveats contains long list of problems with LVM+fsync() in 2011, and a followup message from 2020 claiming all these problems are gone, but apparently, in your case, they aren't.

I wish I could help you with configuring/fixing LVM, but I don't know how.
I wanted to write a simple test C++ program to verify that indeed fsync() is broken in your environment, but realised, that such test would require you to unplug power cord at specific time, which is impractical - otherwise, as long as OS keeps going, it seems to serve even non-fsync()ed yet data directly from OS Cache even if I use O_DIRECT, which makes such synthetic test useless.

The thing I'd try in your situation is to start the server with innodb_force_recovery=6, mysqldump the whole database as SQL, shut down the server, and start from a clean data-dir and restore the database from the SQL dump. Hopefully, even if there are any inconsistencies in the tablespace, most of them could be ignored by a full table scan over leaf-pages of B-tree, which mysqldump should do. The mysqldump tool has various options which should let you ignore/bypass various errors, hopefully letting you extract as much data from tables as possible.

But if the drive has such issues with fsync(), then I'd use a different one, and/or find some expert advice about configuring/fixing it - this is beyond my skill level, unfortunately.

Options: ReplyQuote


Subject
Views
Written By
Posted
Re: Failed to start mysql due to start_lsn and ens_lsn issue
83
August 11, 2022 04:29AM


Sorry, only registered users may post in this forum.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.