ignite-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Alexey Goncharuk <alexey.goncha...@gmail.com>
Subject Re: Reconsider default WAL mode: we need something between LOG_ONLY and FSYNC
Date Wed, 21 Mar 2018 18:23:21 GMT
+1 for fixing LOG_ONLY to enforce corruption safety given the provided
performance results.

2018-03-21 18:20 GMT+03:00 Vladimir Ozerov <vozerov@gridgain.com>:

> +1 for accepting drop in LOG_ONLY. 7% is not that much and not a drop at
> all, provided that we fixing a bug. I.e. should we implement it correctly
> in the first place we would never notice any "drop".
> I do not understand why someone would like to use current broken mode.
>
> On Wed, Mar 21, 2018 at 6:11 PM, Dmitry Pavlov <dpavlov.spb@gmail.com>
> wrote:
>
> > Hi, I think option 1 is better. As Val said any mode that allows
> corruption
> > does not make much sense.
> >
> > What Ivan mentioned here as drop, in relation to old mode DEFAULT (FSYNC
> > now), is still significant perfromance boost.
> >
> > Sincerely,
> > Dmitriy Pavlov
> >
> > ср, 21 мар. 2018 г. в 17:56, Ivan Rakov <ivan.glukos@gmail.com>:
> >
> > > I've attached benchmark results to the JIRA ticket.
> > > We observe ~7% drop in "fair" LOG_ONLY_SAFE mode, independent of WAL
> > > compaction enabled flag. It's pretty significant drop: WAL compaction
> > > itself gives only ~3% drop.
> > >
> > > I see two options here:
> > > 1) Change LOG_ONLY behavior. That implies that we'll be ready to
> release
> > > AI 2.5 with 7% drop.
> > > 2) Introduce LOG_ONLY_SAFE, make it default, add release note to AI 2.5
> > > that we added power loss durability in default mode, but user may
> > > fallback to previous LOG_ONLY in order to retain performance.
> > >
> > > Thoughts?
> > >
> > > Best Regards,
> > > Ivan Rakov
> > >
> > > On 20.03.2018 16:00, Ivan Rakov wrote:
> > > > Val,
> > > >
> > > >> If a storage is in
> > > >> corrupted state, does it mean that it needs to be completely removed
> > and
> > > >> cluster needs to be restarted without data?
> > > >
> > > > Yes, there's a chance that in LOG_ONLY all local data will be lost,
> > > > but only in *power loss**/ OS crash* case.
> > > > kill -9, JVM crash, death of critical system thread and all other
> > > > cases that usually take place are variations of *process crash*. All
> > > > WAL modes (except NONE, of course) ensure corruption-safety in case
> of
> > > > process crash.
> > > >
> > > >> If so, I'm not sure any mode
> > > >> that allows corruption makes much sense to me.
> > > > It depends on performance impact of enforcing power-loss corruption
> > > > safety. Price of full protection from power loss is high - FSYNC is
> > > > way slower (2-10 times) than other WAL modes. The question is whether
> > > > ensuring weaker guarantees (corruption can't happen, but loss of last
> > > > updates can) will affect performance as badly as strong guarantees.
> > > > I'll share benchmark results soon.
> > > >
> > > > Best Regards,
> > > > Ivan Rakov
> > > >
> > > > On 20.03.2018 5:09, Valentin Kulichenko wrote:
> > > >> Guys,
> > > >>
> > > >> What do we understand under "data corruption" here? If a storage is
> in
> > > >> corrupted state, does it mean that it needs to be completely removed
> > and
> > > >> cluster needs to be restarted without data? If so, I'm not sure any
> > mode
> > > >> that allows corruption makes much sense to me. How am I supposed to
> > > >> use a
> > > >> database, if virtually any failure can end with complete loss of
> data?
> > > >>
> > > >> In any case, this definitely should not be a default behavior. If
> > > >> user ever
> > > >> switches to corruption-unsafe mode, there should be a clear warning
> > > >> about
> > > >> this.
> > > >>
> > > >> -Val
> > > >>
> > > >> On Fri, Mar 16, 2018 at 1:06 AM, Ivan Rakov <ivan.glukos@gmail.com>
> > > >> wrote:
> > > >>
> > > >>> Ticket to track changes:
> > > >>> https://issues.apache.org/jira/browse/IGNITE-7754
> > > >>>
> > > >>> Best Regards,
> > > >>> Ivan Rakov
> > > >>>
> > > >>>
> > > >>> On 16.03.2018 10:58, Dmitriy Setrakyan wrote:
> > > >>>
> > > >>>> On Fri, Mar 16, 2018 at 12:55 AM, Ivan Rakov <
> ivan.glukos@gmail.com
> > >
> > > >>>> wrote:
> > > >>>>
> > > >>>> Vladimir,
> > > >>>>> Unlike BACKGROUND, LOG_ONLY provides strict write guarantees
> > > >>>>> unless power
> > > >>>>> loss has happened.
> > > >>>>> Seems like we need to measure performance difference to
decide
> > > >>>>> whether do
> > > >>>>> we need separate WAL mode. If it will be invisible, we'll
just
> fix
> > > >>>>> these
> > > >>>>> bugs without introducing new mode; if it will be perceptible,
> we'll
> > > >>>>> continue the discussion about introducing LOG_ONLY_SAFE.
> > > >>>>> Makes sense?
> > > >>>>>
> > > >>>>> Yes, this sounds like the right approach.
> > > >>>>
> > > >
> > > >
> > >
> > >
> >
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message