[SPARK-12660] [SPARK-14967] [SQL] Implement Except Distinct by Left Anti Join #12736

gatorsmile · 2016-04-27T15:24:16Z

What changes were proposed in this pull request?

Replaces a logical Except operator with a Left-anti Join operator. This way, we can take advantage of all the benefits of join implementations (e.g. managed memory, code generation, broadcast joins).

  SELECT a1, a2 FROM Tab1 EXCEPT SELECT b1, b2 FROM Tab2
  ==>  SELECT DISTINCT a1, a2 FROM Tab1 LEFT ANTI JOIN Tab2 ON a1<=>b1 AND a2<=>b2

Note:

This rule is only applicable to EXCEPT DISTINCT. Do not use it for EXCEPT ALL.
This rule has to be done after de-duplicating the attributes; otherwise, the enerated
join conditions will be incorrect.

This PR also corrects the existing behavior in Spark. Before this PR, the behavior is like

  test("except") {
    val df_left = Seq(1, 2, 2, 3, 3, 4).toDF("id")
    val df_right = Seq(1, 3).toDF("id")

    checkAnswer(
      df_left.except(df_right),
      Row(2) :: Row(2) :: Row(4) :: Nil
    )
  }

After this PR, the result is corrected. We strictly follow the SQL compliance of Except Distinct.

How was this patch tested?

Modified and added a few test cases to verify the optimization rule and the results of operators.

gatorsmile · 2016-04-27T15:26:04Z

cc @hvanhovell Thank you for your quick fix! This PR contains the fix of anti-join: #12730 for avoiding test case failure.

When #12730 is merged, I will remove the related code.

SparkQA · 2016-04-27T16:35:45Z

Test build #57134 has finished for PR 12736 at commit f825dca.

This patch fails Spark unit tests.
This patch merges cleanly.
This patch adds no public classes.

hvanhovell · 2016-04-27T17:17:38Z

Merged fix.

gatorsmile · 2016-04-27T17:20:37Z

Thank you very much! Will clean the code soon

gatorsmile · 2016-04-27T18:13:02Z

sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java

@@ -291,7 +291,7 @@ public void testSetOperation() {
      unioned.collectAsList());

    Dataset<String> subtracted = ds.except(ds2);
-    Assert.assertEquals(Arrays.asList("abc", "abc"), subtracted.collectAsList());
+    Assert.assertEquals(Arrays.asList("abc"), subtracted.collectAsList());


This is pretty strange. I will check the exact behavior of our current Except operator. It sounds like it does not remove the duplicate.

Except apparently does not remove duplicates:

range(0, 10).registerTempTable("a") range(5, 15).registerTempTable("b") sql("(select * from a union all select * from a) except select * from b")

results in:

+---+ | id| +---+ | 2| | 2| | 0| | 0| | 3| | 3| | 4| | 4| | 1| | 1| +---+

So that is weird.

We have to decide what we should do next? This PR is doing Except Distinct.

If we want to keep the existing behavior, which is Except All, we need to change the external API in Dataset.

However, the current SQL interface for Except is wrong. We need to correct it at least.

The current implementation (before this PR) is somewhere between EXCEPT and EXCEPT ALL it will will remove all rows if it finds a match (essentially eliminating duplicates), but it does not remove duplicates where there is no match. Lets follow the principle of least surprise and create a correct EXCEPT (one that removes duplicates).

Uh, I see... Let me add a test case to cover it for ensuring it will not be broken again

This is the example to show why the current master is wrong.

test("except") { val df_left = Seq(1, 2, 2, 3, 3, 4).toDF("id") val df_right = Seq(1, 3).toDF("id") checkAnswer( df_left.except(df_right), Row(2) :: Row(2) :: Row(4) :: Nil ) }

For EXCEPT ALL, we should output

Row(2) :: Row(2) :: Row(3) :: Row(4) :: Nil

For EXCEPT DISTINCT, we should output

Row(2) :: Row(4) :: Nil

Did this PR also fix the semantic of Except, or it only added the optimization?

Yeah. After this PR, the behavior of EXCEPT is changed to the standard behavior of EXCEPT DISTINCT.

SparkQA · 2016-04-27T18:38:26Z

Test build #57143 has finished for PR 12736 at commit 70da501.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

SparkQA · 2016-04-27T21:03:17Z

Test build #57164 has finished for PR 12736 at commit 3c61a5a.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

SparkQA · 2016-04-27T23:46:45Z

Test build #57183 has finished for PR 12736 at commit 7ccd95b.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

gatorsmile · 2016-04-28T01:10:45Z

cc all the people who previously reviewed #10630 : @rxin @marmbrus @cloud-fan @yhuai @nongli

This is ready for review. Thanks!

cloud-fan · 2016-04-28T05:26:32Z

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercionSuite.scala

-
-    // Check if no Project is added
-    assert(r3.left.isInstanceOf[LocalRelation])
-    assert(r3.right.isInstanceOf[LocalRelation])


why remove these? We didn't change the analysis of Except right?

We added a new condition in resolved: https://github.com/apache/spark/pull/12736/files#diff-72917e7b68f0311b2fb42990e0dc616dR180 In this test case, we are trying to Except the same table firstTable. Thus, the value of resolved becomes false now.

When we resolving WidenSetOperationTypes in

spark/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala

Line 230 in c417cec

left.output.length == right.output.length && !s.resolved =>

, the whole if condition becomes true. (Before this PR, this condition is always false if you try to except the same table. Thus, we did nothing in this case. Thus, no Project is added)

However, when if condition becomes true, we execute the corresponding logics. We are able to find the common type. Then, we will add Project. This is doing the duplicate checking like what we did in

spark/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercionSuite.scala

Lines 479 to 490 in d280d1d

val r1 = wt(Except(firstTable, secondTable)).asInstanceOf[Except]

val r2 = wt(Intersect(firstTable, secondTable)).asInstanceOf[Intersect]

checkOutput(r1.left, expectedTypes)

checkOutput(r1.right, expectedTypes)

checkOutput(r2.left, expectedTypes)

checkOutput(r2.right, expectedTypes)

// Check if a Project is added

assert(r1.left.isInstanceOf[Project])

assert(r1.right.isInstanceOf[Project])

assert(r2.left.isInstanceOf[Project])

assert(r2.right.isInstanceOf[Project])

. That is why I removed it.

Sorry, it is a little bit complicated to explain the whole logics. Let me know if anything is not clear

got it, thanks for the explanation!

cloud-fan · 2016-04-28T05:35:08Z

LGTM. A unrelated question, how do we express the EXCEPT ALL semantic?

gatorsmile · 2016-04-28T06:51:35Z

@cloud-fan Thank you for your review!

Like INTERSECT ALL, EXCEPT ALL can be done by aggregation of the union of the two tables. We can augment one table with a new column of constant 1, and the other with constant -1, then union the two tables, and find the row satisfying the result of the COUNT and SUM of the new column.

Originally, I plan to do it after this release. All of you have more time to review them. If we need to implement in this release, I can start writing both INTERSECT ALL and EXCEPT ALL now.

SparkQA · 2016-04-28T08:08:24Z

Test build #57227 has finished for PR 12736 at commit 4920360.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

cloud-fan · 2016-04-29T07:33:15Z

thanks! merging to master!

gatorsmile added 6 commits April 26, 2016 21:20

initial fix

cd6b684

added a test case.

43e7436

antiJoin fix from Herman

89fae2a

added test cases

8397f22

Merge remote-tracking branch 'upstream/master' into exceptByAntiJoin

a104f99

style fix.

f825dca

fixed the test case.

70da501

gatorsmile reviewed Apr 27, 2016
View reviewed changes

Merge remote-tracking branch 'upstream/master' into exceptByAntiJoin

3c61a5a

gatorsmile changed the title ~~[SPARK-12660] [SQL] Implement Except by Left Anti Join~~ [SPARK-12660] [SQL] Implement Except Distinct by Left Anti Join Apr 27, 2016

gatorsmile changed the title ~~[SPARK-12660] [SQL] Implement Except Distinct by Left Anti Join~~ [SPARK-12660] [SPARK-14967] [SQL] Implement Except Distinct by Left Anti Join Apr 27, 2016

one more test case

7ccd95b

cloud-fan reviewed Apr 28, 2016
View reviewed changes

address comments

4920360

asfgit closed this in 222dcf7 Apr 29, 2016

gatorsmile mentioned this pull request Jan 13, 2018

[SPARK-23062][SQL] Improve EXCEPT documentation #20254

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[SPARK-12660] [SPARK-14967] [SQL] Implement Except Distinct by Left Anti Join #12736

[SPARK-12660] [SPARK-14967] [SQL] Implement Except Distinct by Left Anti Join #12736

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	val r1 = wt(Except(firstTable, secondTable)).asInstanceOf[Except]
	val r2 = wt(Intersect(firstTable, secondTable)).asInstanceOf[Intersect]
	checkOutput(r1.left, expectedTypes)
	checkOutput(r1.right, expectedTypes)
	checkOutput(r2.left, expectedTypes)
	checkOutput(r2.right, expectedTypes)

	// Check if a Project is added
	assert(r1.left.isInstanceOf[Project])
	assert(r1.right.isInstanceOf[Project])
	assert(r2.left.isInstanceOf[Project])
	assert(r2.right.isInstanceOf[Project])

[SPARK-12660] [SPARK-14967] [SQL] Implement Except Distinct by Left Anti Join #12736

[SPARK-12660] [SPARK-14967] [SQL] Implement Except Distinct by Left Anti Join #12736

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What changes were proposed in this pull request?

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