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From Mark Pasterkamp <markpasterkamp1...@gmail.com>
Subject Re: ClassCastException RelOptCostImpl VolcanoCost while using HepPlanner
Date Fri, 03 May 2019 17:56:49 GMT
I did not know this is how it works, I just copied the example above.
Would there be an easy way to create a RelNode containg a tablescan over
the materialized view "mv"?
Trying to create one using for instance a relbuilder gives a calcite
exception.
Otherwise I might just look for another test file in which I can get access
to the schema and use the materiaqlizationservice.

Mark

On Fri, 3 May 2019 at 18:35, Jesus Camacho Rodriguez
<jcamachorodriguez@cloudera.com.invalid> wrote:

> bq . Since we are talking about materialized views, I think in most cases
> tableRel should be simply a LogicalTableScan.
>
> Stamatis is correct about this, I had not realized  tableRel == queryRel in
> your sample code.
>
> Thanks,
> Jesús
>
> On Fri, May 3, 2019 at 6:12 AM Stamatis Zampetakis <zabetak@gmail.com>
> wrote:
>
> > I think the main problem comes from the fact that tableRel == queryRel in
> > the test case you provided.
> > Defining the materialized view like that basically says that when you
> find
> > a part of the query that satisfies queryRel replace it with itself.
> > In conjunction with the rule that is used, which allows partial
> rewritings
> > using union, you end up with a rule that matches infinite number of
> times.
> > Since we are talking about materialized views, I think in most cases
> > tableRel should be simply a LogicalTableScan.
> > The idea is that expression represented by queryRel is materialized into
> a
> > table so in order to retrieve the results we only need to scan the table.
> >
> > Regarding the "if (true)" statements that you observed, most likely they
> > were introduced as release toggles [1].
> > However, since the last commit was in 2013 I think by now it is safe to
> > refactor that part and remove dead code.
> >
> > [1] https://www.martinfowler.com/articles/feature-toggles.html
> >
> > Best,
> > Stamatis
> >
> > On Fri, May 3, 2019 at 12:50 PM Mark Pasterkamp <
> > markpasterkamp1994@gmail.com> wrote:
> >
> > > Dear Jesus,
> > >
> > > I think your intuition in this regard is correct.
> > > After executing the main program in the HepPlanner the resulting plan
> > > contains a lot of circular references.
> > > Changing the matching order does not influence this behaviour.
> > >
> > >
> > > Mark
> > >
> > > On Thu, 2 May 2019 at 22:14, Jesus Camacho Rodriguez
> > > <jcamachorodriguez@cloudera.com.invalid> wrote:
> > >
> > > > Mark,
> > > >
> > > > I have an intuition that this happens because the rule creates a
> > > partially
> > > > contained rewriting with a union, where one side contains a scan over
> > the
> > > > materialized view and the other side contains the query itself with a
> > > > filter on top excluding the data that is coming from the materialized
> > > view.
> > > > Then the rule is triggered on the plan representing the original
> query
> > > > again and the process is repeated. Have you tried changing the
> matching
> > > > order for your hep program?
> > > >
> > > > Thanks,
> > > > Jesús
> > > >
> > > > On Thu, May 2, 2019 at 8:53 AM Mark Pasterkamp <
> > > > markpasterkamp1994@gmail.com>
> > > > wrote:
> > > >
> > > > > Hi Stamatis,
> > > > >
> > > > > I have tried to recreate the issue but I have not been able to do
> > > that. I
> > > > > was however able to create a new exception which I don't quite
> > > > understand.
> > > > > The error happened when calcite was creating a union rewriting
> using
> > > > > materialized views. But trying to recreate this situation gave me
> > > another
> > > > > interesting one.
> > > > > This time, the planner rewrites one of the children nodes into
> > itself I
> > > > > would assume which causes a stack overflow. The method itself can
> be
> > > > found
> > > > > here:
> > > > >
> > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/mpasterkamp/calcite/blob/768b7928dbde5f6f9775a1119e7466d8eafafb4b/core/src/test/java/org/apache/calcite/test/HepPlannerTest.java#L312
> > > > >
> > > > > Perhaps I am doing something wrong, perhaps not? I am not
> > knowledgeable
> > > > > enough about this to understand why this is happening. Wish I could
> > > help
> > > > > more for that.
> > > > >
> > > > > Also, while investigating this issue I found another interesting
> > > artifact
> > > > > in de source code of the VolcanoCost. A lot of methods in this
> class
> > > have
> > > > > an "if (true)"-statement like here:
> > > > >
> > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/apache/calcite/blob/4b4d8037c5073e4eb5702b12bc4ecade31476616/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoCost.java#L100
> > > > >
> > > > > Now I was just curious, is there any reason for this to be there
> that
> > > you
> > > > > know of?
> > > > >
> > > > > Thank you for responding and congratulations for your recent
> > > promotions.
> > > > >
> > > > >
> > > > > With kind regards,
> > > > >
> > > > > Mark
> > > > >
> > > > >
> > > > > On Thu, 2 May 2019 at 14:58, Stamatis Zampetakis <
> zabetak@gmail.com>
> > > > > wrote:
> > > > >
> > > > > > Said like that it looks like a bug.
> > > > > >
> > > > > > I think the best would be to reproduce the exception as a unit
> test
> > > in
> > > > > > HepPlannerTest [1], RelOptRulesTest [2], or PlannerTest [3]
so
> that
> > > we
> > > > > > could understand better the use case.
> > > > > >
> > > > > > [1]
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/apache/calcite/blob/master/core/src/test/java/org/apache/calcite/test/HepPlannerTest.java
> > > > > > [2]
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/apache/calcite/blob/master/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java
> > > > > > [3]
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/apache/calcite/blob/master/core/src/test/java/org/apache/calcite/tools/PlannerTest.java
> > > > > >
> > > > > > On Thu, May 2, 2019 at 7:56 AM Mark Pasterkamp <
> > > > > > markpasterkamp1994@gmail.com>
> > > > > > wrote:
> > > > > >
> > > > > > > I don't, I would assume that the HepPlanner.findBestExp()
> > > calculates
> > > > > the
> > > > > > > cost somewhere down the line
> > > > > > >
> > > > > > > On Thu, May 2, 2019, 03:31 Yuzhao Chen <yuzhao.cyz@gmail.com>
> > > wrote:
> > > > > > >
> > > > > > > > Why you care about cost when use HepPlanner ? The
HepPlanner
> is
> > > > aimed
> > > > > > for
> > > > > > > > some deterministic planning rules, we usually do not
need
> cost
> > in
> > > > > Hep.
> > > > > > > Some
> > > > > > > > exceptions like Join reorder may need a cost.
> > > > > > > >
> > > > > > > > What kind of planning promotion you did ? I'm kind
of curious
> > > about
> > > > > it.
> > > > > > > >
> > > > > > > > Best,
> > > > > > > > Danny Chan
> > > > > > > > 在 2019年5月1日 +0800 PM9:27,Mark Pasterkamp
<
> > > > > markpasterkamp1994@gmail.com
> > > > > > > > >,写道:
> > > > > > > > > Dear all,
> > > > > > > > >
> > > > > > > > > While playing around with the HepPlanner I ran
into an
> issue
> > > > where
> > > > > > the
> > > > > > > > > planner wants to rewrite a query with a union
rewrite. When
> > the
> > > > > > > > > RelMetaDataQuery computes the cost, the cost
instance is a
> > > > > > VolcanoCost.
> > > > > > > > > Then when it tries to calculate the cost of one
of the
> > union's
> > > > > > operands
> > > > > > > > it
> > > > > > > > > is a RelCostImpl which results in the ClassCastException.
> > > > > > > > >
> > > > > > > > > How would I go about solving this issue? As far
as my
> > knowledge
> > > > > > goes, I
> > > > > > > > am
> > > > > > > > > not able to change the costhandler of the RelMetaDataQuery.
> > > > Another
> > > > > > > > > approach I could see is removing the cast in
the
> VolcanoCost
> > > > class,
> > > > > > > but I
> > > > > > > > > would hope I do not have to do that.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > With kind regards,
> > > > > > > > >
> > > > > > > > > Mark
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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