[jira] [Commented] (CALCITE-3224) New RexNode-to-Expression CodeGen Implementation

["Stamatis Zampetakis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-3224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16897856#comment-16897856 ] 

Stamatis Zampetakis commented on CALCITE-3224:
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Hey [~donnyzone] thanks a lot for this PR! Overall, I like the approach and your high level description is great. Although, I agree with the refactoring that you did I would suggest to avoid it for now. It is much more difficult to perform the review by comparing code in different files.

I would consider keeping the new code as close to the old code as possible till the PR gets merged. We could perform the refactoring into separate classes and files in another PR. I don't know if other people share this opinion so feel free to ignore my comment if nobody else raises this concern. 

> New RexNode-to-Expression CodeGen Implementation
> ------------------------------------------------
>
>                 Key: CALCITE-3224
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3224
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 1.20.0
>            Reporter: Feng Zhu
>            Assignee: Feng Zhu
>            Priority: Critical
>              Labels: pull-request-available
>         Attachments: codegen.png
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> h3. *Background*
>     Current RexNode-to-Expression implementation relies on BlockBuilder's incorrect “optimizations” to inline unsafe operations. As illustrated in CALCITE-3173, when this cooperation is broken in some special cases, it will cause exceptions like NPE, such as CALCITE-3142, CALCITE-3143, CALCITE-3150.
>     Though we can fix these problems under current implementation framework with some efforts like the PR in CALCITE-3142, the logic will become more and more complex. To pursue a thorough and elegant solution, we implement a new one. Moreover, it also ensures the correctness for non-optimized code.
> h3. *Major Features*
>  * *Visitor Pattern*: Each RexNode will be visited only once in a bottom-up way, rather than recursively visiting a RexNode many times with different NullAs settings.
>  * *Conditional Semantic*: It can naturally guarantee the correctness even without BlockBuilder’s “optimizings”. Each line of code generated for a RexNode is null safe.
>  * *Interface Compatibility*: The implementation only updates _RexToLixTranslator_ and _RexImpTable_. Interfaces such as CallImplementor keep unchanged.
> h3. *Implementation*
>     For each RexNode, the visitor will generally generate two declaration statements, one for value and one for nullable. The code snippet is like:
> {code:java}
> {valueVariable} = {valueExpression}
> {isNullVariable} = {isNullExpression}
> {code}
> The visitor’s result will be the variable pair (*_isNullVariable_*, *_valueVariable_*).
> *Other changes:*
> (1) ReImplement different RexCall implementations (e.g., CastImplementor, BinaryImplementor and etc.) as seperated files and remove them into the newly created package _org.apache.calcite.adapter.enumerable.rex,_ and organize them in RexCallImpTable.
> (2) move some util functions into EnumUtils.
> h3. *Example Demonstration*
> Take a simple test case as example, in which the "commission" column is nullable.
> {code:java}
> @Test public void testNPE() {
>   CalciteAssert.hr()
>     .query("select \"commission\" + 10 as s\n"
>       + "from \"hr\".\"emps\"")
>     .returns("S=1010\nS=510\nS=null\nS=260\n");
> }
> {code}
> The codegen progress and non-optimized code are demonstrated in the figure below.
> !codegen.png!
>  # When visiting *RexInputRef (commission)*, the visitor generates three lines of code, the result is a pair of ParameterExpression (*_input_isNull_*, *_input_value_*).
>  # Then the visitor visits *RexLiteral (10)* and generates two lines of code. The result is (*_literal_isNull_*, *_literal_value_*).
>  # After that, when visiting *RexCall(Add)*, (_*input_isNull*_, _*input_value*_) and (_*literal_isNull*_, _*literal_value*_) can be used to implement the logic. The visitor also generates two lines of code and return the variable pair.
> In the end, the result Expression is constructed based on (_*binary_call_isNull*_, _*binary_call_value*_)



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