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Re: fsync alternative


Maybe buy battery based raid card

Em sáb, 7 de set de 2019 às 15:27, Jure Sah <dustwolfy@xxxxxxxxx> escreveu:

> Hi,
> It would appear that on a typical webserver, the majority of disk i/o
> belongs to the MariaDB database process. It would appear it's mostly
> waiting on fsync(), which to my understanding is executed at least once
> per commit.
> I understand that this is extensively researched in the documentation
> and it has to do with the recovery of data in case of an unexpected
> server reboot.
> The thing is, this has many performance issues because it caps database
> performance at whatever the speed of the underlying physical storage is,
> even if the changed data fits into the available RAM. It also results in
> the circumstance where if anything is impacting performance of the
> storage system on the server, this will break MariaDB and cause the
> service to go offline (time out), even if there is sufficient RAM in the
> machine to continue operating as normal from page cache.
> In a typical scenario you have a website which is writing things like
> session and page cache data which expires within an hour and would be no
> great loss if missing from a backup. Especially if the volume of the
> missing data would be 30 seconds (kernel default for committing dirty
> pages to disk) and mind you this setting is configurable.
> Temporary tables cannot be used in this case, because they are deleted
> as soon as the session ends, which is too soon.
> Is there a different solution that could be used here?
> I've also noticed in the documentation that the options to control fsync
> usage are even more limited than in the MySQL server. They are also very
> strongly argued against. Considering the point that InnoDB is considered
> to be in an inconsistent state in any event, so long as the server is
> not cleanly stopped, is there really justification for such strong
> opposition here?
> Disabling fsync boosts performance of a typical MySQL server by
> something like a factor of 3.
> LP,
> Jure
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Roberto Spadim
SPAEmpresarial - Software ERP/Scada
Eng. Automação e Controle, Eng. Financeira