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From Vladislav Pyatkov <vldpyat...@gmail.com>
Subject Re: PRIMARY_SYNC+readFromBackup semantics
Date Wed, 04 Oct 2017 09:09:42 GMT
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

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