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Re: MariaDB server horribly slow on start


You can try it, but that isn't a fix, that is a way to make the
flushing run all the time at full rate.
If I remember correctly, old behaviour was that the flushing would
happen at innodb_io_capacity rate, and above the hwm, it would kick
into innodb_io_capacity_max rate.
Or something along those lines.
On 10.5+ you get only two speeds, 0 and whatever your disks can handle
(which can also starve other I/O)
Whatever the "improvement" intended was, the outcome is a substantial downgrade.

On Wed, Jul 27, 2022 at 3:36 PM Cédric Counotte
<cedric.counotte@xxxxxxxxxx> wrote:
> Reading this: https://jira.mariadb.org/browse/MDEV-27295
> It's quite unclear when it is fixed or reverted.
> That said I read that the following setting might fix it:
>         SET GLOBAL innodb_max_dirty_pages_pct_lwm=0.001;
> Is that correct and should I try that and see if that helps?
> -----Message d'origine-----
> De : Gordan Bobic <gordan.bobic@xxxxxxxxx>
> Envoyé : mercredi 27 juillet 2022 14:29
> À : Marko Mäkelä <marko.makela@xxxxxxxxxxx>
> Cc : Cédric Counotte <cedric.counotte@xxxxxxxxxx>; Mailing-List mariadb <maria-discuss@xxxxxxxxxxxxxxxxxxx>
> Objet : Re: [Maria-discuss] MariaDB server horribly slow on start
> On Wed, Jul 27, 2022 at 3:08 PM Marko Mäkelä <marko.makela@xxxxxxxxxxx> wrote:
> >
> > On Wed, Jul 27, 2022 at 2:48 PM Gordan Bobic <gordan.bobic@xxxxxxxxx> wrote:
> > >
> > > There is no supported downgrade path other than logical dump+restore.
> > > There are also no packages built for distros where the major version is older than what ships with the distro.
> > >
> > > Since your queries seem to end up stuck in commit stage, it could be related to redo log flushing, which behaves very erratically on 10.5+. If it leaves the log to fill up to 90% and the state transfer hits, it could be that with the checkpoint age already high, there just isn't enough headroom to avoid a massive stall. Purely guessing here without any telemetry.
> >
> > I think that you may refer to InnoDB page flushing. There was some
> > misunderstanding around that, and indeed some partly unintended or
> > uninformed changes in behaviour (in 10.5.7 and 10.5.8) that were
> > reverted later. It could be useful to read
> > https://jira.mariadb.org/browse/MDEV-27295.
> What version was it reverted in?
> I am still seeing the errant redo log flushing behaviour in 10.5.15.
> It looks like no flushing happens until the hwm is reached at about 85% full. It then tries to commit everything down to the lwm. And inbetween it doesn't do anything, even while everything is idle and it should be running down the