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https://issues.apache.org/jira/browse/CALCITE-786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14630256#comment-14630256
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Julian Hyde commented on CALCITE-786:
-------------------------------------
bq. The real pain point currently is that for executor (in
RexImplicationchecker) to execute, we need to give it a data context which
should contain values of particular Java type. Now this requires converting
data from one type to another and this is the messy part of my code, as it has
to handle many combinations of input datatype and expected datatype. Any
suggestions on how to go about it especially for type Date as partitioning on
column of type Date is pretty common and a very important use case ?
Since you're dealing with RexNodes, the constants will be of the types used
internally by RexLiteral: BigDecimal for numbers, Calendar for date-times, etc.
So you just need to handle those types.
Also, rely on Executor as much as you can. It is tasked with implementing SQL
semantics (3 valued boolean logic, conversions using CAST, implicit rounding
and truncation and all that hard stuff). If you don't trust Executor, write a
test. I've just added RexExecutorTest.checkConstant so you can easily check
that say, DATE '2015-07-15' < DATE '2015-07-15' reduces to FALSE.
I will squash and commit shortly, and then I will mark this issue closed.
Please start developing on top of that commit as soon as it is checked in.
> Detect if materialized view can be used to rewrite a query in non-trivial
> cases
> -------------------------------------------------------------------------------
>
> Key: CALCITE-786
> URL: https://issues.apache.org/jira/browse/CALCITE-786
> Project: Calcite
> Issue Type: Task
> Components: core
> Affects Versions: 1.3.0-incubating, 1.4.0-incubating
> Reporter: Amogh Margoor
> Assignee: Julian Hyde
> Priority: Minor
> Fix For: next
>
>
> Improvement to detection if MV can be used to rewrite queries in non-trivial
> cases.
> Pasting the email conversation below that happened over this which briefly
> discusses the approach taken:
> ---------- Forwarded message ----------
> From: Amogh Margoor <[email protected]>
> Date: Fri, Jun 26, 2015 at 10:11 AM
> Subject: Re: Detect if materialized view can be used to rewrite a query in
> non-trivial cases
> To: [email protected], Rajat Venkatesh <[email protected]>
> Hi Julian,
> Thanks a lot Julian for your feedback. I have inlined my response below which
> also includes the commit done.
> Regards,
> Amogh
> On Fri, Jun 26, 2015 at 1:05 AM, Julian Hyde <[email protected]> wrote:
> This is great work. Certainly consistent with where I am heading.
> I would not be inclined to use DNF (because of its tendency to inflate
> certain predicates) but if you are able to get something effective I
> will happily use it. I think you should package it behind a method --
> "find out what is left to satisfy p when you have already satisfied q"
> or something -- and write lots of tests of that method, and it doesn't
> really matter what algorithm is behind it.
> Take a look at SubstitutionVisitor.simplfy(RexNode) and how it focuses
> on finding whether
> p1 AND p2 AND p3 AND NOT (q1 AND q2 AND q3)
> is satisfiable.
> >> I saw this method. I will try to use this in improvements to follow.
> >> It didnot seem to solve this currently: (x>10 => x>30) i.e., find if
> >> NOT (NOT(x>10 ) OR x >30) is satisfiable.
> >> We have currently packaged it as "if X => Y" (see RexImplicationChecker
> >> in the commit I shared below), but agree it should be
> >> more generic like what you suggested above and something we can try to
> >> achieve.
> Later we will want to know not just "can I satisfy query Q using
> materialization M?" but "can I satisfy part of Q using M, and what is
> left over?". I can convert most of Q to use an aggregate table over
> years 2012 .. 2014 and 2015 Jan - May, and then scan the raw data for
> June 1st onwards, that is a big win.
> >> This certainly should be something we should aim at.
> What branch are you working on? Your master branch
> https://github.com/qubole/incubator-calcite/tree/master seems to be
> the same as apache/master right now.
> >> We work on https://github.com/qubole/incubator-calcite/tree/qds-1.3 .
> >> This is the commit:
> >> https://github.com/qubole/incubator-calcite/pull/1/files?diff=unified
> >> We are in the process of writing UTs for it. We did most of the testing
> >> through our client code till now.
> >> We have created new Visitor extending SustitutionVisitor because did not
> >> want to mess with the existing code.
> >> More rules need to be added to the new Visitor.
> >> Will raise a PR once UTs are added and testing is complete.
>
> If you can divide this work into pull requests with unit tests, I will
> happy commit each change as you make progress.
> By the way, I logged a few jira cases connected to materialized view
> rewrite today. They were motivated by the phoenix team wanting to use
> secondary indexes. But they could by applied to any scan-project-sort
> materialization. See
> * https://issues.apache.org/jira/browse/CALCITE-771
> * https://issues.apache.org/jira/browse/CALCITE-772
> * https://issues.apache.org/jira/browse/CALCITE-773
> >> Thanks for sharing this info Julian. Will definitely take a look.
> Julian
> On Thu, Jun 25, 2015 at 11:46 AM, Amogh Margoor <[email protected]> wrote:
> > Hi,
> > We were working on a problem to detect if materialized view can be used
> to
> > rewrite a query in non-trivial cases. Will briefly describe the problem
> and
> > approach below and would appreciate feedback on the same.
> >
> > Motivation
> > ---------------
> > For instance there exists a table "logs" and a partition (materialized
> > view) named "log_after_01_Jan" created on it and described by SQL :
> > "Select * from logs where log_date > '01-01-2015' ".
> >
> > Assume that the table "log_after_01_Jan" is much smaller than table
> "logs".
> >
> > For user query:
> > "Select log_body from logs where log_date > '03-03-2015' and
> > char_length(log_body) < 100",
> > we should detect that the materialized view "log_after_01_Jan" can be
> used
> > and transform the query into:
> >
> > "Select log_body from log_after_01_Jan where log_date > '03-03-2015' and
> > char_length(log_body) < 100"
> >
> > Approach
> > --------------
> > One of the fundamental problems we would come across here is to check
> if a
> > boolean condition X implies (=>) Y. This quickly reduces to the
> > Satisfiability problem which is NP complete for propositional logic. But
> > there are many instances like above which can be detected easily. We
> have
> > implemented an approach to handle several useful cases for few operators
> > and types of operands. Will be extending it further for more types of
> > operations.
> >
> > Top Level approach:
> >
> > 1. Currently, VolcanoPlanner:useMaterialization tries to rewrite
> original
> > query using MV using SubstitutionVisitor. Have extended
> SubstitutionVisitor
> > to detect above cases and do the substitution.
> >
> > 2. To check if a condition X => Y,
> > a. Convert both of them into Disjunctive Normal Form.
> > Say X is transformed into x_1 or x_2 or x_3 ... or x_m and
> > Y is transformed into y_1 or y_2 ,... or y_i, where any x_i and
> y_i
> > are conjunctions of atomic predicates.
> > For instance condition "(a>10 or b>20) and c <90" will be
> converted
> > to DNF: (a>10 and c<90) or (b>20 and c<90).
> >
> > b. For X=>Y to be a tautology i.e., hold always true, every
> conjunction
> > x_i should imply atleast one of the conjunction y_j.
> > We wrote some set of simple heuristics to check if a conjunction
> of
> > atomic predicates implies another.
> > This also involves executing RexNode using RexImplExecutor.
> >
> > We have checked in code for this in our fork of
> > calcite(qubole/incubator-calcite). This is ongoing work and we will be
> > making many more improvements to it. If this is useful or anybody is
> > interested in giving feedback then I can share the commit so that we can
> > discuss about it and take it forward.
> >
> > Regards,
> > Amogh
> > Member of Technical Staff
> > Qubole
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