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From: Yingyi Bu <buyingyi@gmail.com>
Date: Mon, 31 Oct 2016 11:23:13 -0700
Message-ID: <CALjEsF7o2OTuENq9T4yqFwLgmSyExU374=Wja70z-ezFZu3KbQ@mail.gmail.com>
Subject: Re: About the Multiple Join Optimization on AsterixDB
To: dev@asterixdb.apache.org
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archived-at: Mon, 31 Oct 2016 18:23:22 -0000

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Mingda,

     I'm not sure how much re-ordering can be done at the Hyracks level,
i.e., the runtime level.
     In the optimizer (the asterixdb/algebricks level), we don't have
re-ordering for  joins, because:
     --- the cost model has not been added yet.  I'm not sure about the
timeline for this. @Ildar?
     --- respecting user-specified join orders is important for certain
cases, for example, to get stable/predictable performance (zero surprise)
for applications.

     In the runtime, we have a role-reversal optimization in hybrid hash
join, which is a safe optimization that is not based on estimations.  You
can look at OptimizedHybridHashJoin.

Best,
Yingyi


On Mon, Oct 31, 2016 at 11:16 AM, mingda li <limingda1993@gmail.com> wrote:

> Dear all,
>
> Hi, I am working on multiple join on Hyracks level. I am not sure if I do
> the multiple join on AsterixDB, whether it will optimize the query by
> changing the join order or just execute according to how we write the
> query. I think this may not be done in Algebricks level based on rule but
> not sure.
>
> Bests,
> Mingda
>

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