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Re: Re: Exception-handling in built-in functions


Hi,

Thanks for opening this discussion and thank you all for your replies.

The reason why I would like to help solve CALCITE-525 is because I agree that an function error should not easily break a large job, this "job" could indicate a large ad-hoc query or a query on a stream, or like what Julian said, a ETL job.
According to some tests I had run about Calcite streaming, a simple division by zero error could break the whole query job. Say, If Calcite does not provide a option to silence the error, users should spend extract daily time on checking whether their streaming job is alive if their SQL includes a "/" operator.

The solutions of B and C are different: B is to ignore and drop a whole row when error happens, and C is to make the failed call return null value. In C, the major reason to introduce "CATCH_ERROR" function is to represent the error handling on Rel, whether to enable the function in Parser is not important.
At first I personally prefer C, but as C does need more code change than B, I don't have a very strong inclination between B and C now.

At last, I agree that making enough discussion on introducing new feature is very important. If we don't really need such a feature now, I think I can help whenever it is considered helpful in future.

Thanks,
Hongze
 
From: Jesus Camacho Rodriguez
Date: 2018-10-18 10:26
To: dev@xxxxxxxxxxxxxxxxxx
Subject: Re: Exception-handling in built-in functions
I do not believe there is enough reason to block CALCITE-525. IMO, CALCITE-525 describes a problem that some Calcite users are facing and a reasonable plugable solution. We should not be vetoing such a feature without providing viable alternatives. (Without having checked the specific implementation details, I prefer approach B described below as it is less intrusive. And A should be fixed in a different issue.)
I agree with Julian´s idea that Calcite is not a RDBMS such as Oracle or Postgres, and it has always tried to provide flexibility to underlying engines, one of the reasons for its wide adoption. In addition, systems are not forced to use this feature, it is tagged as experimental and by default we are still running in same mode. I believe that is sufficient.
Personally, I will not be happy if a developer feels compelled to fork Calcite or stop contributing code because we do not accept features such as the one described there.
 
Thanks,
Jesús
 
 
On 10/17/18, 5:17 PM, "Michael Mior" <mmior@xxxxxxxxxx> wrote:
 
    My apologies for missing this thread a couple days ago. (Thanks for pinging
    it.) Here's my two cents: taking care of contributors to the project is
    just as important (if not more important) than taking care of the code. I'm
    not saying we should merge terrible code just to keep each other happy, but
    I don't think that's the case here. If anyone writes some code which you
    disagree with, you should be free to voice your disagreement. However,
    especially when the code is from a core contributor and the argument
    focuses on potential future problems, I think it's important to consider
    that people who have shown dedication to the project over the years are
    very likely to be around and willing to fix these problems as they arise.
    
    Code which turns out to cause problems can always be deleted, reverted,
    refactored, etc. It's much harder to back out when a contributor is burned
    out or interpersonal conflicts get heated.
    
    --
    Michael Mior
    mmior@xxxxxxxxxx
    
    
    Le mer. 17 oct. 2018 à 14:58, Julian Hyde <jhyde@xxxxxxxxxx> a écrit :
    
    > Vladimir,
    >
    > You’ve made your points. And I hear them.
    >
    > However I get the impression that you are not open to persuasion. Which
    > means that I am wasting my time trying to reach consensus with you. Which
    > means that people win arguments not on merit, but based upon who is most
    > persistent.
    >
    > Here is my point. Calcite's goal is not to re-create what Oracle or
    > PostgreSQL did ten years later. It is a platform that allows people to
    > write their own data engine. If they want to redefine the “+” operator such
    > that 2 + 2 returns 5, the platform should allow it.
    >
    > Certainly if they want to engineer their own error-handling strategy, we
    > should let them do it. I didn’t have the energy to find an example of a SQL
    > engine that discards rows with divide-by-zero errors, but I believe there
    > is one. I suspect that both Broadbase, SQLstream and Hive, three SQL
    > engines that I have worked on that performed ETL-like tasks, all had that
    > capability. And all ETL tools have very flexible error-handling strategies.
    > They are not SQL-based, but Calcite is not exclusively for SQL systems.
    >
    > I have been designing and building world-class data engines for 30 years.
    > Please take me on good faith that a flexible error-handing strategy is a
    > good idea. Don’t force me to bicker over email for hours and hours. When a
    > long discussion leads to the rejection of a contribution, I get
    > considerably closer to burning out.
    >
    > Julian
    >
    >
    > > On Oct 17, 2018, at 11:36 AM, Vladimir Sitnikov <
    > sitnikov.vladimir@xxxxxxxxx> wrote:
    > >
    > > Juilian>Hey, folks. We need your input here.
    > >
    > > Here are my thoughts:
    > > 1) I think the features we add should have at least some level of
    > > consistency
    > > 2) It is much safer to adopt well-known features rather than be pioneers
    > in
    > > the field. I do not mean we must wait for someone else implement and try
    > > out a feature, however I would not rush for implementing a feature that
    > > no-one else explored.
    > >
    > > CALCITE-525 has two key points:
    > > A) Current implementation of enumerable factors code like 0/0 to a static
    > > field of a generated code. It causes the generated code to fail at load
    > > time even before the query is executed.
    > > Of course that is a bug, and I'm even inclined to remove that "static
    > > fields"
    > >
    > > B) Someone (Hongze? Juilan?) suggest to implement a mode to silently
    > ignore
    > > the error (e.g. by ignoring the row or by returning default value).
    > > First of all, I don't think "ignore the row" kind of processing would do
    > > any good to the user since it would not be possible to predict the
    > output.
    > > "ignore the row" is very tricky when join/semijoin/antijoin is there.
    > >
    > > I'm sure OracleDB and PostgreSQL do NOT have such "features", so I think
    > we
    > > should not rush for it.
    > >
    > > C) Hongze suggests  CATCH_ERROR(1 / 0  EMPTY ON ERROR) or CATCH_ERROR(1 /
    > > 0)  EMPTY ON ERROR  kind of functions.
    > > That enables to confine the scope of the error, however I don't think it
    > > would be used often (does that mean one would have to wrap each
    > > expression?), and this "catch error" would be non-trivial to propagate to
    > > the downstream executors.
    > > On top of that, we might end up inventing full-blown
    > try-catch-catch-catch
    > > syntax.
    > >
    > > I truly see no business value in implementing B/C, however I do see the
    > > pain it would introduce. It would complicate Calcite maintenance. "B"
    > could
    > > silently produce wrong results, and I'm sure we don't want get results
    > out
    > > of thin air.
    > >
    > > Vladimir
    >
    >