[jira] [Comment Edited] (DRILL-6524) Two CASE statements in projection influence results of each other

["Volodymyr Vysotskyi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-6524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16788807#comment-16788807 ] 

Volodymyr Vysotskyi edited comment on DRILL-6524 at 3/12/19 4:33 PM:
---------------------------------------------------------------------

The problem here is connected with incorrect scalar replacement. It still happens even for the case when a reference to the object outside of the conditional block is changed inside the conditional block. It causes wrong results for the case when code in this conditional block will not be executed.
The code below demonstrates this issue:

Original class:
{code:java}
package org.apache.drill;

import org.apache.drill.exec.expr.holders.NullableBigIntHolder;

public class CompileClassWithIfs {

  public static void doSomething() {
    int a = 2;
    NullableBigIntHolder out0 = new NullableBigIntHolder();
    out0.isSet = 1;
    NullableBigIntHolder out4 = new NullableBigIntHolder();
    out4.isSet = 0;
    NullableBigIntHolder out5 = new NullableBigIntHolder();

    if (a == 0) {
      out0 = out4;
    } else {
    }

    if (out4.isSet == 0) {
      out0.isSet = 1;
      out5.value = 3;
    } else {
      out0.isSet = 0;
      assert false : "Incorrect class transformation. This code should never be executed.";
    }
  }
}
{code}

Code after scalar replacement:
{code:java}
package org.apache.drill;

public class CompileClassWithIfs {
  public static void doSomething() {
    byte var0 = 2;
    boolean var1 = false;
    long var2 = 0L;
    var1 = true;
    boolean var4 = false;
    long var5 = 0L;
    var4 = false;
    boolean var7 = false;
    long var8 = 0L;
    if (var0 == 0) {
      var1 = var4;
    }

    if (!var1) {
      var1 = true;
      var8 = (long)3;
    } else {
      var1 = false;
      if (true) {
        throw new AssertionError("Incorrect class transformation. This code should never be executed.");
      }
    }

  }

  public CompileClassWithIfs() {
  }
}
{code}

Please note that in the original code, assertion error will not be thrown, but after scalar replacement {{out0}} and {{out4}} have the same values, so they were inlined using the same variables.

Code after the changes in https://github.com/apache/drill/pull/1686:
{code:java}
package org.apache.drill;

import org.apache.drill.exec.expr.holders.NullableBigIntHolder;

public class CompileClassWithIfs {
  public static void doSomething() {
    byte var0 = 2;
    NullableBigIntHolder var1 = new NullableBigIntHolder();
    var1.isSet = 1;
    NullableBigIntHolder var2 = new NullableBigIntHolder();
    var2.isSet = 0;
    boolean var3 = false;
    long var4 = 0L;
    if (var0 == 0) {
      var1 = var2;
    }

    if (var2.isSet == 0) {
      var1.isSet = 1;
      var4 = (long)3;
    } else {
      var1.isSet = 0;
      if (true) {
        throw new AssertionError("Incorrect class transformation. This code should never be executed.");
      }
    }

  }

  public CompileClassWithIfs() {
  }
}
{code}

Please note, that two {{NullableBigIntHolder}} objects whose references were assigned to each other in if the block weren't replaced since it is impossible to produce the correct replacement.


was (Author: vvysotskyi):
The problem here is connected with incorrect scalar replacement. It still happens even for the case when a reference to the object outside of the conditional block is changed inside the conditional block. It causes wrong results for the case when code in this conditional block will not be executed.
The code below demonstrates this issue:

Original class:
{code:java}
package org.apache.drill;

import org.apache.drill.exec.expr.holders.NullableBigIntHolder;

public class CompileClassWithIfs {

  public static void doSomething() {
    int a = 2;
    NullableBigIntHolder out0 = new NullableBigIntHolder();
    out0.isSet = 1;
    NullableBigIntHolder out4 = new NullableBigIntHolder();
    out4.isSet = 0;
    if (a == 0) {
      out0 = out4;
    } else {
    }

    if (out4.isSet == 0) {
      out0.isSet = 1;
    } else {
      out0.isSet = 0;
      assert false : "incorrect value";
    }
  }
}
{code}

Code after scalar replacement:
{code:java}
package org.apache.drill;

public class CompileClassWithIfs {
  public static void doSomething() {
    int a = 2;
    boolean var1 = false;
    long var2 = 0L;
    var1 = true;
    boolean var4 = false;
    long var5 = 0L;
    var4 = false;
    if (a == 0) {
      var1 = var4;
    }

    if (!var1) {
      var1 = true;
    } else {
      var1 = false;
      if (true) {
        throw new AssertionError("incorrect value");
      }
    }

  }

  public CompileClassWithIfs() {
  }
}
{code}

Please note that in the original code, assertion error will not be thrown, but after scalar replacement {{out0}} and {{out4}} have the same values, so they were inlined using the same variables.

> Two CASE statements in projection influence results of each other
> -----------------------------------------------------------------
>
>                 Key: DRILL-6524
>                 URL: https://issues.apache.org/jira/browse/DRILL-6524
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Query Planning & Optimization
>    Affects Versions: 1.11.0
>         Environment: Linux 3.10.0-693.21.1.el7.x86_64 #1 SMP Wed Mar 7 19:03:37 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux,
> NAME="CentOS Linux"
> VERSION="7 (Core)"
> apache drill 1.11.0, 
> openjdk version "1.8.0_171"
> OpenJDK Runtime Environment (build 1.8.0_171-b10)
> OpenJDK 64-Bit Server VM (build 25.171-b10, mixed mode)
>            Reporter: Oleksandr Chornyi
>            Assignee: Volodymyr Vysotskyi
>            Priority: Major
>             Fix For: 1.16.0
>
>
> h3. Steps to Reproduce
> Run the following query via {{sqlline}}:
> {code:sql}
> select
>   case when expr$0 = 3 then expr$0 else expr$1 end,
>   case when expr$0 = 1 then expr$0 else expr$1 end
> from (values(1, 2));
> {code}
> h4. Actual Results
> {noformat}
> +---------+---------+
> | EXPR$0  | EXPR$1  |
> +---------+---------+
> | 2       | 2       |
> +---------+---------+
> {noformat}
> h4. Expected Results
> {noformat}
> +---------+---------+
> | EXPR$0  | EXPR$1  |
> +---------+---------+
> | 2       | 1       |
> +---------+---------+
> {noformat}
> Note, that changing order of CASE statements fixes the issue. The following query yields correct results:
> {code:sql}
> select
>   case when expr$0 = 1 then expr$0 else expr$1 end,
>   case when expr$0 = 3 then expr$0 else expr$1 end
> from (values(1, 2));
> {code}



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