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From Alexei Scherbakov <alexey.scherbak...@gmail.com>
Subject Re: PRIMARY_SYNC+readFromBackup semantics
Date Wed, 04 Oct 2017 10:27:59 GMT
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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