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From Ivan Rakov <ivan.glu...@gmail.com>
Subject Re: Forbid mixed cache groups with both atomic and transactional caches
Date Wed, 05 Feb 2020 10:46:37 GMT
Ivan,

Thanks for pointing this out. Less than one day is indeed too early to
treat this discussion thread as a "community conclusion". Still, the
consensus among the current participants made me feel that a conclusion
will be reached.
We'll surely get back to the discussion if opposite opinions will arise.

On Wed, Feb 5, 2020 at 1:11 PM Ivan Pavlukhin <vololo100@gmail.com> wrote:

> Folks,
>
> A bit of offtop. Do we have some recommendations in the community how
> long should we wait until treating something as "a Community
> conclusion"? It worries me a little bit that I see a discussion for a
> first time and there is already a conclusion. And the discussion was
> started lesser than 24 hours ago. I suppose we should allow everyone
> interested to share an opinion (here I agree with the proposal) and it
> usually requires some time in open-source communities.
>
> ср, 5 февр. 2020 г. в 10:58, Ivan Rakov <ivan.glukos@gmail.com>:
> >
> > Folks,
> >
> > Thanks for your feedback.
> > I've created a JIRA issue on this change:
> > https://issues.apache.org/jira/browse/IGNITE-12622
> >
> > On Tue, Feb 4, 2020 at 10:43 PM Denis Magda <dmagda@apache.org> wrote:
> >
> > > +1 from my end. It doesn't sound like a big deal if Ignite users need
> to
> > > define separate groups for atomic and transactional caches.
> > >
> > > -
> > > Denis
> > >
> > >
> > > On Tue, Feb 4, 2020 at 3:28 AM Ivan Rakov <ivan.glukos@gmail.com>
> wrote:
> > >
> > > > Igniters,
> > > >
> > > > Apparently it's possible in Ignite to configure a cache group with
> both
> > > > ATOMIC and TRANSACTIONAL caches.
> > > > Proof: IgniteCacheGroupsTest#testContinuousQueriesMultipleGroups*
> tests.
> > > > In my opinion, it would be better to remove such possibility from the
> > > > product. There are several reasons:
> > > >
> > > > 1) The original idea of grouping caches was optimizing storage
> overhead
> > > and
> > > > PME time by joining data of similar caches into the same partitions.
> > > ATOMIC
> > > > and TRANSACTIONAL caches provide different guarantees and are
> designed
> > > for
> > > > different use cases, thus they can hardly be called "similar".
> > > >
> > > > 2) Diving deeper: synchronization protocols and possible reasons for
> > > > primary-backup divergences are conceptually different for ATOMIC and
> > > > TRANSACTIONAL cases. In TRANSACTIONAL case, transactions recovery
> > > protocol
> > > > allows to recover consistency if any participating node will fail,
> but
> > > for
> > > > ATOMIC caches there's possible scenario with failure of primary node
> > > where
> > > > neither of backups will contain the most recent state of the data.
> > > Example:
> > > > one backup have received updates 1, 3, 5 while another have received
> 2, 4
> > > > (which is possible due to message reordering), and even tracking
> counters
> > > > [1] won't restore the consistency. The problem is that we can't
> > > distinguish
> > > > what kind of conflict we have faced in case update counters have
> diverged
> > > > in a mixed group.
> > > >
> > > > 3) Mixed groups are poorly tested. I can't find any tests except a
> couple
> > > > of smoke tests in IgniteCacheGroupsTest. We can't be sure that
> different
> > > > synchronization protocols will work correctly for such
> configurations,
> > > > especially under load and with a variety of dependent configuration
> > > > parameters.
> > > >
> > > > 4) I have never heard of any feedback on mixed groups. I have asked
> > > > different people on this and no one recalled any attempts to
> configure
> > > such
> > > > groups. I believe that in fact no one has ever tried to do it.
> > > >
> > > > Please let me know if you are aware of any cases where mixed groups
> are
> > > > used or reasons to keep them. Otherwise I'll create a ticket to
> prohibit
> > > > mixed configurations.
> > > >
> > > > [1]: https://issues.apache.org/jira/browse/IGNITE-11797
> > > >
> > > > --
> > > > Best Regards,
> > > > Ivan Rakov
> > > >
> > >
>
>
>
> --
> Best regards,
> Ivan Pavlukhin
>

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