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From Valentin Kulichenko <valentin.kuliche...@gmail.com>
Subject Re: PRIMARY_SYNC+readFromBackup semantics
Date Wed, 04 Oct 2017 23:50:58 GMT
FULL_SYNC as default is not a solution. PRIMARY_SYNC/readFromBackup is
valid combination of parameters and useful in many scenarios. For example,
what if I have a replicated cache and don't want to update all nodes
synchronously?

The point is that get() invoked after the put() in the same thread should
always return the latest value. Now this behavior is not consistent and
depends on which nodes these operations are executed on.

-Val

On Wed, Oct 4, 2017 at 3:27 AM, Alexei Scherbakov <
alexey.scherbakoff@gmail.com> wrote:

> Val,
>
> Totally agreed.
>
> I think this can be easily fixed by setting FULL_SYNC as default sync mode.
>
> Actually, I do not understand why this is not done yet.
>
> 2017-10-04 12:09 GMT+03:00 Vladislav Pyatkov <vldpyatkov@gmail.com>:
>
> > Hi Val,
> >
> > If we update local backup immediate synchronously when sending commit to
> > primary, this only partly removes questions about consistence view.
> > But we always can to get other (unpredictable) value, because another
> > transaction will be executed simultaneously from other threads.
> >
> > At the same time this is good place for optimization, probably reduce
> > network overhead.
> > I think, need to create a ticket in Jira for the improvement.
> >
> >
> > On Tue, Oct 3, 2017 at 12:27 AM, Valentin Kulichenko <
> > valentin.kulichenko@gmail.com> wrote:
> >
> > > Igniters,
> > >
> > > I noticed that combination of PRIMARY_SYNC mode and readFromBackup=true
> > > (both are default values BTW) introduces weird semantics when reading
> > *on a
> > > backup node*. Basically, if I do put and then get for the same key in
> the
> > > same thread, I can get previous value. In my understanding, this
> happens
> > > because even local backup is updated asynchronously in this case.
> > >
> > > First of all, this is obviously confusing and would be considered as a
> > bug
> > > by most of the users (I just updated the key with some value, why
> would I
> > > get another value when reading it?).
> > >
> > > Second of all, it seems that we send a network message from primary
> node
> > to
> > > local backup, which doesn't make much sense to me and looks like
> > > unnecessary performance overhead.
> > >
> > > Is it possible to update local backup synchronously in this scenario?
> > >
> > > -Val
> > >
> >
> >
> >
> > --
> > Vladislav Pyatkov
> >
>
>
>
> --
>
> Best regards,
> Alexei Scherbakov
>

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