I suppose some approaches used by classic databases makes no sense for Ignite. FSYNC requirement for databases has the nature of single host solution. If you have corrupted db files you have corrupted (lost) data.
For Ignite the enough number of backups and the failure detecting logic can provide the data consistency in term "cluster data consistency". On Fri, Feb 16, 2018 at 8:57 PM, Dmitry Pavlov <dpavlov....@gmail.com> wrote: > Hi, all WAL modes except NONE protects from data consistency problem > (B+Tree, pages, etc), which is why I suggest to avoid saying 'corrupted' > about 'unapplied updates'. > > Log Only and Background may cause unapplied updates in case of OS/process > failures. > > None mode IMO is not an option in case data consistency is needed. > > пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko < > valentin.kuliche...@gmail.com>: > > > Guys, > > > > While we're on this topic, what is the difference between BACKGROUND and > > NONE in terms of semantics and provided guarantees? To me it looks like > > both guarantee to recover the state since last checkpoint and anything > else > > can potentially be lost, so from user perspective they are the same. Am I > > missing something here? > > > > Also there is the following in Javadoc for NONE: "If an Ignite node is > > terminated in NONE mode abruptly, it is likely that the data stored on > disk > > is corrupted and work directory will need to be cleared for a node > > restart.". If this is really the case, I'm not sure NONE makes sense at > > all. Why would I enable persistence if I'm likely to clear the storage on > > restart? > > > > -Val > > > > On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <voze...@gridgain.com> > > wrote: > > > > > What is the reason to have DEFAULT mode at all if you claim LOG_ONLY to > > be > > > completely safe? :) > > > > > > And how it could be safe provided that without fsync we loose part of > WAL > > > itself in case of crash? > > > > > > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <dpavlov....@gmail.com>: > > > > > > > Thank you. Data can't be corrupted in case crash because of WAL > replay > > > > (since completed checkpoint). Physical records are used to restore > > > probably > > > > corrupted pages in persistent store (we overwrite so called 'grey > > zone' - > > > > pages we don't know for sure if they have been written). > > > > > > > > Only one effect is unwritten one or several last transactions. It is > > not > > > > the same with corrupted data. > > > > > > > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <voze...@gridgain.com > >: > > > > > > > > > Log only mode is not safe - data might be corrupted in case of > system > > > > > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync, > > Cassandra > > > - > > > > > similar to our “background”. > > > > > > > > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <dpavlov....@gmail.com > >: > > > > > > > > > > > Hi Vladimir, > > > > > > > > > > > > What you saying is defenetely make sence. > > > > > > > > > > > > In the same time LOG_ONLY is also safe mode, user will be able to > > > > restore > > > > > > system after crash. If it is not true, we should create critical > > > ticket > > > > > and > > > > > > fix it. > > > > > > > > > > > > Do you know other databases defaults, such as Cassandra, Oracle, > > > > Postgre? > > > > > > > > > > > > Sincerely, > > > > > > Dmitriy Pavlov > > > > > > > > > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov < > > voze...@gridgain.com > > > >: > > > > > > > > > > > > > Igniters, > > > > > > > > > > > > > > Sorry for pouring oil on the flames, but from database > > perspective > > > > > moving > > > > > > > from FSYNC to non-FSYNC mode appears to be a mistake. When you > > work > > > > > with > > > > > > > database, your main expectation is that it will save your data. > > All > > > > > > > production database vendor make sure that you are safe, not > that > > > you > > > > > are > > > > > > > fast. Moreover, some vendors even prevent you from being in > > unsafe > > > > mode > > > > > > > (e.g. you cannot disable fsync in SQL Server at all). > > > > > > > > > > > > > > If we continue going in this direction, we will end up with a > > > > product, > > > > > > > which is unsafe out of the box and require tons of > documentation > > to > > > > > > > understand how to make it safe. Definitely not the right > message > > to > > > > the > > > > > > > market. This is like a car without brakes - would you like to > > drive > > > > it? > > > > > > If > > > > > > > this is Need For Speed game and you have unlimited lives > > (in-memory > > > > > cache > > > > > > > with backing store), then yes. If this is a real life with > > > > > (persistence) > > > > > > - > > > > > > > then no. > > > > > > > > > > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan < > > > > > > dsetrak...@apache.org> > > > > > > > wrote: > > > > > > > > > > > > > > > Well, I cannot say that I like the name LOG_ONLY, but I would > > > vote > > > > to > > > > > > > keep > > > > > > > > it for now, given that it is already documented in many > places, > > > > > blogs, > > > > > > > and > > > > > > > > examples. > > > > > > > > > > > > > > > > D. > > > > > > > > > > > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov < > > > ivan.glu...@gmail.com > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Looks like it's an Ignite term - I've never heard of it > > outside > > > > > > Ignite > > > > > > > > > scope. > > > > > > > > > > > > > > > > > > Though, renaming existing enum value requires keeping old > as > > > > > > > deprecated. > > > > > > > > > DEFAULT is confusing enough to pay this price. > > > > > > > > > As for LOG_ONLY, I think we can keep it as long as it has > > good > > > > and > > > > > > > > > definitive javadoc. > > > > > > > > > > > > > > > > > > Best Regards, > > > > > > > > > Ivan Rakov > > > > > > > > > > > > > > > > > > > > > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote: > > > > > > > > > > > > > > > > > >> Igniters, just to clarify, does the term LOG_ONLY mean > > > anything > > > > in > > > > > > the > > > > > > > > >> industry or is this just an Ignite term? > > > > > > > > >> > > > > > > > > >> D. > > > > > > > > >> > > > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov < > > > > > > > > >> avinogra...@gridgain.com> > > > > > > > > >> wrote: > > > > > > > > >> > > > > > > > > >> Log only mode: flushes application buffers. > > > > > > > > >>> So, in synced mode without fsync guarantee. That's why I > > > > propose > > > > > to > > > > > > > > >>> rename > > > > > > > > >>> it as SYNC. > > > > > > > > >>> > > > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh < > > > > > > ilant...@gridgain.com > > > > > > > > > > > > > > > > >>> wrote: > > > > > > > > >>> > > > > > > > > >>> I am OK with either FSYNC or STRICT variant. > > > > > > > > >>>> > > > > > > > > >>>> LOG_ONLY name means "log without fsync". > > > > > > > > >>>> > > > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan < > > > > > > > > >>>> > > > > > > > > >>> dsetrak...@apache.org> > > > > > > > > >>> > > > > > > > > >>>> wrote: > > > > > > > > >>>> > > > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov < > > > > > > ivan.glu...@gmail.com> > > > > > > > > >>>>> > > > > > > > > >>>> wrote: > > > > > > > > >>>> > > > > > > > > >>>>> Why create a new term to define something that has > > already > > > > been > > > > > > > > >>>>>> > > > > > > > > >>>>> defined? > > > > > > > > >>>> > > > > > > > > >>>>> That makes sense. I'm ok with FSYNC. > > > > > > > > >>>>>> Anton, I don't understand why we should rename > LOG_ONLY > > to > > > > > SYNC. > > > > > > > We > > > > > > > > >>>>>> started this discussion with bad naming of DEFAULT, > but > > > this > > > > > has > > > > > > > > >>>>>> > > > > > > > > >>>>> nothing > > > > > > > > >>>> > > > > > > > > >>>>> to > > > > > > > > >>>>> > > > > > > > > >>>>>> do with LOG_ONLY (even though it may be scientific - > but > > > > SYNC > > > > > > > sounds > > > > > > > > >>>>>> scientific as well). > > > > > > > > >>>>>> > > > > > > > > >>>>>> I agree with Ivan, we should not go wild with > renaming. > > > > > > However, I > > > > > > > > >>>>> > > > > > > > > >>>> would > > > > > > > > >>> > > > > > > > > >>>> like to find out what is the meaning behind the LOG_ONLY > > > name. > > > > > Can > > > > > > > > >>>>> > > > > > > > > >>>> someone > > > > > > > > >>>> > > > > > > > > >>>>> explain? > > > > > > > > >>>>> > > > > > > > > >>>>> D. > > > > > > > > >>>>> > > > > > > > > >>>>> > > > > > > > > >>>> > > > > > > > > >>>> -- > > > > > > > > >>>> Best regards, > > > > > > > > >>>> Ilya > > > > > > > > >>>> > > > > > > > > >>>> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- Sergey Kozlov GridGain Systems www.gridgain.com
