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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 07:58:42 GMT
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
> >
>

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