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Re: How to report progress for InnoDB background tasks (esp. at startup/shutdown)?


Hi, Marko!

On Apr 07, Marko Mäkelä wrote:
> Hi all,
> MariaDB Server features a nice-looking interface for reporting progress on
> long-running SQL operations:
> https://mariadb.com/kb/en/mariadb/progress-reporting/
> MySQL 5.7 implemented something similar for reporting progress for ALTER
> TABLE…ALGORITHM=INPLACE. I should reimplement that for MariaDB using the
> existing MariaDB infrastructure.
> I wonder if the same interface could be used for tracking progress on
> periodic background tasks that might not be directly related to the
> execution of any SQL statements. InnoDB has a number of background tasks,
> such as:
> * purging unneeded history (removing undo log records and delete-marked
> index records)
> * rolling back recovered transactions (mainly, if the server was killed)
> * index defragmentation, encryption key rotation
> * redo log checkpoints (flush all dirty pages up to the checkpoint LSN;
> most interesting at shutdown)

Yes and no. InnoDB background threads can report the progress. They'll
need a THD for that. Luckily, purge threads already have it in 10.2.
The progress will be shown in SHOW PROCESSLIST, but won't be sent
to a client in special progress report packets.

I suspect it should be fairly easy to start using progress reporting in
purge threads. And then you could see whether it makes sense to enable
it for more background threads.

> Related to this, I wonder if it is possible or feasible to change the
> SQL layer logic so that at shutdown, it will not issue ROLLBACK (as
> part of KILL QUERY) to the currently active connections, but let the
> subsequent startup do the rollback in the background. This should
> allow faster shutdowns and restarts.

I don't see why not. From the user point of view an aborted (with a
shutdown or a disconnect) transaction should always be rolled back. But
how exactly it's implemented is up to us, as long as the user visible
behavior stays the same.

Chief Architect MariaDB
and security@xxxxxxxxxxx

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