+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.glu...@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 >
