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From: Valentin Kulichenko <valentin.kulichenko@gmail.com>
Date: Tue, 18 Apr 2017 10:04:20 +0200
Message-ID: <CABuYRcoawSYV1c+eToc6zDWHt_XZT7sFyURK+0vXLxa9HBHXaw@mail.gmail.com>
Subject: Re: Performance vs correctness: I vote fore the second
To: dev@ignite.apache.org
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archived-at: Tue, 18 Apr 2017 08:05:01 -0000

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Can you please elaborate then? What is the logic there?

-Val

On Tue, Apr 18, 2017 at 9:55 AM, Sergi Vladykin <sergi.vladykin@gmail.com>
wrote:

> Val,
>
> That discussion has nothing to do with this PRIMARY_SYNC problem.
>
> Sergi
>
> 2017-04-18 10:51 GMT+03:00 Valentin Kulichenko <
> valentin.kulichenko@gmail.com>:
>
> > Sergi,
> >
> > I'm talking about this discussion:
> > http://apache-ignite-developers.2346864.n4.nabble.
> > com/SQL-on-PARTITIONED-vs-REPLICATED-cache-td16478.html
> >
> > -Val
> >
> > On Tue, Apr 18, 2017 at 9:46 AM, Vladimir Ozerov <vozerov@gridgain.com>
> > wrote:
> >
> > > Val,
> > >
> > > PRIMARY_SYNC doesn't work correctly with the most common case of SQL
> > query
> > > execution over REPLICATED cache. Also it has weird consequences for
> > > continuous queries when coupled with another
> performance-over-correctness
> > > property "readFromBackup=true": user may receive CQ notification with
> new
> > > value, but subsequent GET on local node may return old value.
> > >
> > > On Tue, Apr 18, 2017 at 10:42 AM, Valentin Kulichenko <
> > > valentin.kulichenko@gmail.com> wrote:
> > >
> > > > This sounds more like an issue with query execution, rather than
> wrong
> > > > PRIMARY_SYNC
> > > > behavior. We already had a discussion about this optimization in
> > > replicated
> > > > cache and decided to switch it off by default.
> > > >
> > > > -Val
> > > >
> > > > On Tue, Apr 18, 2017 at 9:35 AM, Sergi Vladykin <
> > > sergi.vladykin@gmail.com>
> > > > wrote:
> > > >
> > > > > With replicated cache we can execute a query against backup
> > partitions
> > > > that
> > > > > were not updated yet because of PRIMARY_SYNC. Thus we do not see an
> > > > update.
> > > > >
> > > > > Sergi
> > > > >
> > > > > 2017-04-18 10:30 GMT+03:00 Dmitriy Setrakyan <
> dsetrakyan@apache.org
> > >:
> > > > >
> > > > > > Vladimir,
> > > > > >
> > > > > > What is wrong with a query in PRIMARY_SYNC mode? Why won't it
> work?
> > > > > >
> > > > > > D.
> > > > > >
> > > > > > On Tue, Apr 18, 2017 at 12:25 AM, Vladimir Ozerov <
> > > > vozerov@gridgain.com>
> > > > > > wrote:
> > > > > >
> > > > > > > Folks,
> > > > > > >
> > > > > > > I received a number of complaints from users that our default
> > > setting
> > > > > > favor
> > > > > > > performance at the cost of correctness and subtle behavior.
> > > > Yesterday I
> > > > > > > faced one such situation on my own.
> > > > > > >
> > > > > > > I started REPLICATED cache on several nodes, put some data,
> > > executed
> > > > > > simple
> > > > > > > SQL and got wrong result. No errors, no warnings. The problem
> was
> > > > > caused
> > > > > > by
> > > > > > > default PRIMARY_SYNC mode. WTF, our cache doesn't work out of
> the
> > > > box!
> > > > > > >
> > > > > > > Another widely known examples are data streamer behavior, "read
> > > form
> > > > > > > backups" + continuous queries.
> > > > > > >
> > > > > > > I propose to change our defaults to favor *correctness* over
> > > > > performance,
> > > > > > > and create good documentation and JavaDocs to explain users how
> > to
> > > > tune
> > > > > > our
> > > > > > > product. Proposed changes:
> > > > > > >
> > > > > > > 1) FULL_SYNC as default;
> > > > > > > 2) "readFromBackups=false" as default;
> > > > > > > 3) "IgniteDataStreamer.allowOverwrite=true" as default.
> > > > > > >
> > > > > > > Users should not think how to make Ignite work correctly. It
> > should
> > > > be
> > > > > > > correct out of the box.
> > > > > > >
> > > > > > > Vladimir.
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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