[
https://issues.apache.org/jira/browse/SPARK-26352?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16722697#comment-16722697
]
ASF GitHub Bot commented on SPARK-26352:
----------------------------------------
asfgit closed pull request #23303: [SPARK-26352][SQL] join reorder should not
change the order of output attributes
URL: https://github.com/apache/spark/pull/23303
This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:
As this is a foreign pull request (from a fork), the diff is supplied
below (as it won't show otherwise due to GitHub magic):
diff --git
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
index 064ca68b7a628..01634a9d852c6 100644
---
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
+++
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
@@ -48,6 +48,7 @@ object CostBasedJoinReorder extends Rule[LogicalPlan] with
PredicateHelper {
if projectList.forall(_.isInstanceOf[Attribute]) =>
reorder(p, p.output)
}
+
// After reordering is finished, convert OrderedJoin back to Join
result transformDown {
case OrderedJoin(left, right, jt, cond) => Join(left, right, jt, cond)
@@ -175,11 +176,20 @@ object JoinReorderDP extends PredicateHelper with Logging
{
assert(topOutputSet == p.outputSet)
// Keep the same order of final output attributes.
p.copy(projectList = output)
+ case finalPlan if !sameOutput(finalPlan, output) =>
+ Project(output, finalPlan)
case finalPlan =>
finalPlan
}
}
+ private def sameOutput(plan: LogicalPlan, expectedOutput: Seq[Attribute]):
Boolean = {
+ val thisOutput = plan.output
+ thisOutput.length == expectedOutput.length &&
thisOutput.zip(expectedOutput).forall {
+ case (a1, a2) => a1.semanticEquals(a2)
+ }
+ }
+
/** Find all possible plans at the next level, based on existing levels. */
private def searchLevel(
existingLevels: Seq[JoinPlanMap],
diff --git
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
index 6ebb194d71c2e..0b6471289a471 100644
---
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
+++
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
@@ -86,9 +86,9 @@ object ReorderJoin extends Rule[LogicalPlan] with
PredicateHelper {
}
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
- case ExtractFiltersAndInnerJoins(input, conditions)
+ case p @ ExtractFiltersAndInnerJoins(input, conditions)
if input.size > 2 && conditions.nonEmpty =>
- if (SQLConf.get.starSchemaDetection && !SQLConf.get.cboEnabled) {
+ val reordered = if (SQLConf.get.starSchemaDetection &&
!SQLConf.get.cboEnabled) {
val starJoinPlan = StarSchemaDetection.reorderStarJoins(input,
conditions)
if (starJoinPlan.nonEmpty) {
val rest = input.filterNot(starJoinPlan.contains(_))
@@ -99,6 +99,14 @@ object ReorderJoin extends Rule[LogicalPlan] with
PredicateHelper {
} else {
createOrderedJoin(input, conditions)
}
+
+ if (p.sameOutput(reordered)) {
+ reordered
+ } else {
+ // Reordering the joins have changed the order of the columns.
+ // Inject a projection to make sure we restore to the expected
ordering.
+ Project(p.output, reordered)
+ }
}
}
diff --git
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinOptimizationSuite.scala
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinOptimizationSuite.scala
index ccd9d8dd4d213..e9438b2eee550 100644
---
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinOptimizationSuite.scala
+++
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinOptimizationSuite.scala
@@ -102,16 +102,19 @@ class JoinOptimizationSuite extends PlanTest {
x.join(y).join(z).where(("x.b".attr === "z.b".attr) && ("y.d".attr ===
"z.a".attr)),
x.join(z, condition = Some("x.b".attr === "z.b".attr))
.join(y, condition = Some("y.d".attr === "z.a".attr))
+ .select(Seq("x.a", "x.b", "x.c", "y.d", "z.a", "z.b",
"z.c").map(_.attr): _*)
),
(
x.join(y, Cross).join(z, Cross)
.where(("x.b".attr === "z.b".attr) && ("y.d".attr === "z.a".attr)),
x.join(z, Cross, Some("x.b".attr === "z.b".attr))
.join(y, Cross, Some("y.d".attr === "z.a".attr))
+ .select(Seq("x.a", "x.b", "x.c", "y.d", "z.a", "z.b",
"z.c").map(_.attr): _*)
),
(
x.join(y, Inner).join(z, Cross).where("x.b".attr === "z.a".attr),
x.join(z, Cross, Some("x.b".attr === "z.a".attr)).join(y, Inner)
+ .select(Seq("x.a", "x.b", "x.c", "y.d", "z.a", "z.b",
"z.c").map(_.attr): _*)
)
)
diff --git
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinReorderSuite.scala
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinReorderSuite.scala
index 565b0a10154a8..c94a8b9e318f6 100644
---
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinReorderSuite.scala
+++
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinReorderSuite.scala
@@ -20,8 +20,8 @@ package org.apache.spark.sql.catalyst.optimizer
import org.apache.spark.sql.catalyst.dsl.expressions._
import org.apache.spark.sql.catalyst.dsl.plans._
import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeMap}
-import org.apache.spark.sql.catalyst.plans.{Inner, PlanTest}
-import org.apache.spark.sql.catalyst.plans.logical.{ColumnStat, LogicalPlan}
+import org.apache.spark.sql.catalyst.plans.{Cross, Inner, PlanTest}
+import org.apache.spark.sql.catalyst.plans.logical.{ColumnStat, LocalRelation,
LogicalPlan}
import org.apache.spark.sql.catalyst.rules.RuleExecutor
import org.apache.spark.sql.catalyst.statsEstimation.{StatsEstimationTestBase,
StatsTestPlan}
import org.apache.spark.sql.internal.SQLConf.{CBO_ENABLED,
JOIN_REORDER_ENABLED}
@@ -124,7 +124,8 @@ class JoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
// the original order (t1 J t2) J t3.
val bestPlan =
t1.join(t3, Inner, Some(nameToAttr("t1.v-1-10") ===
nameToAttr("t3.v-1-100")))
- .join(t2, Inner, Some(nameToAttr("t1.k-1-2") === nameToAttr("t2.k-1-5")))
+ .join(t2, Inner, Some(nameToAttr("t1.k-1-2") ===
nameToAttr("t2.k-1-5")))
+ .select(outputsOf(t1, t2, t3): _*)
assertEqualPlans(originalPlan, bestPlan)
}
@@ -139,7 +140,9 @@ class JoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
val bestPlan =
t1.join(t3, Inner, Some(nameToAttr("t1.v-1-10") ===
nameToAttr("t3.v-1-100")))
.join(t2, Inner, Some(nameToAttr("t1.k-1-2") ===
nameToAttr("t2.k-1-5")))
+ .select(outputsOf(t1, t2, t3): _*) // this is redundant but we'll take
it for now
.join(t4)
+ .select(outputsOf(t1, t2, t4, t3): _*)
assertEqualPlans(originalPlan, bestPlan)
}
@@ -202,6 +205,7 @@ class JoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
t1.join(t2, Inner, Some(nameToAttr("t1.k-1-2") ===
nameToAttr("t2.k-1-5")))
.join(t4.join(t3, Inner, Some(nameToAttr("t4.v-1-10") ===
nameToAttr("t3.v-1-100"))),
Inner, Some(nameToAttr("t1.k-1-2") === nameToAttr("t4.k-1-2")))
+ .select(outputsOf(t1, t4, t2, t3): _*)
assertEqualPlans(originalPlan, bestPlan)
}
@@ -219,6 +223,23 @@ class JoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
}
}
+ test("SPARK-26352: join reordering should not change the order of
attributes") {
+ // This test case does not rely on CBO.
+ // It's similar to the test case above, but catches a reordering bug that
the one above doesn't
+ val tab1 = LocalRelation('x.int, 'y.int)
+ val tab2 = LocalRelation('i.int, 'j.int)
+ val tab3 = LocalRelation('a.int, 'b.int)
+ val original =
+ tab1.join(tab2, Cross)
+ .join(tab3, Inner, Some('a === 'x && 'b === 'i))
+ val expected =
+ tab1.join(tab3, Inner, Some('a === 'x))
+ .join(tab2, Cross, Some('b === 'i))
+ .select(outputsOf(tab1, tab2, tab3): _*)
+
+ assertEqualPlans(original, expected)
+ }
+
test("reorder recursively") {
// Original order:
// Join
@@ -266,8 +287,17 @@ class JoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
private def assertEqualPlans(
originalPlan: LogicalPlan,
groundTruthBestPlan: LogicalPlan): Unit = {
- val optimized = Optimize.execute(originalPlan.analyze)
+ val analyzed = originalPlan.analyze
+ val optimized = Optimize.execute(analyzed)
val expected = groundTruthBestPlan.analyze
+
+ assert(analyzed.sameOutput(expected)) // if this fails, the expected plan
itself is incorrect
+ assert(analyzed.sameOutput(optimized))
+
compareJoinOrder(optimized, expected)
}
+
+ private def outputsOf(plans: LogicalPlan*): Seq[Attribute] = {
+ plans.map(_.output).reduce(_ ++ _)
+ }
}
diff --git
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinCostBasedReorderSuite.scala
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinCostBasedReorderSuite.scala
index d4d23ad69b2c2..baae934e1e4fe 100644
---
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinCostBasedReorderSuite.scala
+++
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinCostBasedReorderSuite.scala
@@ -218,6 +218,7 @@ class StarJoinCostBasedReorderSuite extends PlanTest with
StatsEstimationTestBas
.join(d1, Inner, Some(nameToAttr("f1_fk1") === nameToAttr("d1_pk")))
.join(t2, Inner, Some(nameToAttr("f1_c2") === nameToAttr("t2_c1")))
.join(t1, Inner, Some(nameToAttr("f1_c1") === nameToAttr("t1_c1")))
+ .select(outputsOf(f1, t1, t2, d1, d2): _*)
assertEqualPlans(query, expected)
}
@@ -256,6 +257,7 @@ class StarJoinCostBasedReorderSuite extends PlanTest with
StatsEstimationTestBas
.join(t3.join(t2, Inner, Some(nameToAttr("t2_c2") ===
nameToAttr("t3_c1"))), Inner,
Some(nameToAttr("d1_c2") === nameToAttr("t2_c1")))
.join(t1, Inner, Some(nameToAttr("t1_c1") === nameToAttr("f1_c1")))
+ .select(outputsOf(d1, t1, t2, f1, d2, t3): _*)
assertEqualPlans(query, expected)
}
@@ -297,6 +299,7 @@ class StarJoinCostBasedReorderSuite extends PlanTest with
StatsEstimationTestBas
Some(nameToAttr("t3_c1") === nameToAttr("t4_c1")))
.join(t1.join(t2, Inner, Some(nameToAttr("t1_c1") ===
nameToAttr("t2_c1"))), Inner,
Some(nameToAttr("t1_c2") === nameToAttr("t4_c2")))
+ .select(outputsOf(d1, t1, t2, t3, t4, f1, d2): _*)
assertEqualPlans(query, expected)
}
@@ -347,6 +350,7 @@ class StarJoinCostBasedReorderSuite extends PlanTest with
StatsEstimationTestBas
Some(nameToAttr("d3_c2") === nameToAttr("t1_c1")))
.join(t5.join(t6, Inner, Some(nameToAttr("t5_c2") ===
nameToAttr("t6_c2"))), Inner,
Some(nameToAttr("d2_c2") === nameToAttr("t5_c1")))
+ .select(outputsOf(d1, t3, t4, f1, d2, t5, t6, d3, t1, t2): _*)
assertEqualPlans(query, expected)
}
@@ -375,6 +379,7 @@ class StarJoinCostBasedReorderSuite extends PlanTest with
StatsEstimationTestBas
f1.join(d3, Inner, Some(nameToAttr("f1_fk3") === nameToAttr("d3_pk")))
.join(d2, Inner, Some(nameToAttr("f1_fk2") === nameToAttr("d2_pk")))
.join(d1, Inner, Some(nameToAttr("f1_fk1") === nameToAttr("d1_pk")))
+ .select(outputsOf(d1, d2, f1, d3): _*)
assertEqualPlans(query, expected)
}
@@ -400,13 +405,27 @@ class StarJoinCostBasedReorderSuite extends PlanTest with
StatsEstimationTestBas
f1.join(t3, Inner, Some(nameToAttr("f1_fk3") === nameToAttr("t3_c1")))
.join(t2, Inner, Some(nameToAttr("f1_fk2") === nameToAttr("t2_c1")))
.join(t1, Inner, Some(nameToAttr("f1_fk1") === nameToAttr("t1_c1")))
+ .select(outputsOf(t1, f1, t2, t3): _*)
assertEqualPlans(query, expected)
}
private def assertEqualPlans( plan1: LogicalPlan, plan2: LogicalPlan): Unit
= {
- val optimized = Optimize.execute(plan1.analyze)
+ val analyzed = plan1.analyze
+ val optimized = Optimize.execute(analyzed)
val expected = plan2.analyze
+
+ assert(equivalentOutput(analyzed, expected)) // if this fails, the
expected itself is incorrect
+ assert(equivalentOutput(analyzed, optimized))
+
compareJoinOrder(optimized, expected)
}
+
+ private def outputsOf(plans: LogicalPlan*): Seq[Attribute] = {
+ plans.map(_.output).reduce(_ ++ _)
+ }
+
+ private def equivalentOutput(plan1: LogicalPlan, plan2: LogicalPlan):
Boolean = {
+ normalizeExprIds(plan1).output == normalizeExprIds(plan2).output
+ }
}
diff --git
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinReorderSuite.scala
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinReorderSuite.scala
index 4e0883e91e84a..9dc653b9d6c44 100644
---
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinReorderSuite.scala
+++
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinReorderSuite.scala
@@ -182,6 +182,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d1, Inner, Some(nameToAttr("f1_fk1") === nameToAttr("d1_pk1")))
.join(d3, Inner, Some(nameToAttr("f1_fk3") === nameToAttr("d3_pk1")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") === nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, d2, f1, d3, s3): _*)
assertEqualPlans(query, expected)
}
@@ -220,6 +221,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d3, Inner, Some(nameToAttr("f1_fk3") === nameToAttr("d3_pk1")))
.join(d2, Inner, Some(nameToAttr("f1_fk2") < nameToAttr("d2_pk1")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") === nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, f1, d2, s3, d3): _*)
assertEqualPlans(query, expected)
}
@@ -255,7 +257,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d3, Inner, Some(nameToAttr("d3_fk1") === nameToAttr("s3_pk1")))
.join(d2, Inner, Some(nameToAttr("f1_fk2") === nameToAttr("d2_pk1")))
.join(s3, Inner, Some(nameToAttr("f1_fk3") === nameToAttr("s3_c2")))
-
+ .select(outputsOf(d1, f1, d2, s3, d3): _*)
assertEqualPlans(query, expected)
}
@@ -292,6 +294,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d3, Inner, Some(nameToAttr("f1_fk3") === nameToAttr("d3_pk1")))
.join(d2, Inner, Some(nameToAttr("f1_fk2") === nameToAttr("d2_c2")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") < nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, f1, d2, s3, d3): _*)
assertEqualPlans(query, expected)
}
@@ -395,6 +398,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d2.where(nameToAttr("d2_c2") === 2), Inner,
Some(nameToAttr("f1_fk2") === nameToAttr("d2_pk1")))
.join(s3, Inner, Some(nameToAttr("f11_fk1") === nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, f11, f1, d2, s3): _*)
assertEqualPlans(query, equivQuery)
}
@@ -430,6 +434,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d2.where(nameToAttr("d2_c2") === 2), Inner,
Some(nameToAttr("f1_fk2") === nameToAttr("d2_c4")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") === nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, d3, f1, d2, s3): _*)
assertEqualPlans(query, expected)
}
@@ -465,6 +470,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d2.where(nameToAttr("d2_c2") === 2), Inner,
Some(nameToAttr("f1_fk2") === nameToAttr("d2_pk1")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") === nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, d3, f1, d2, s3): _*)
assertEqualPlans(query, expected)
}
@@ -499,6 +505,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d2.where(nameToAttr("d2_c2") === 2),
Inner, Some(nameToAttr("f1_fk2") === nameToAttr("d2_pk1")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") === nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, d3, f1, d2, s3): _*)
assertEqualPlans(query, expected)
}
@@ -532,6 +539,7 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d3, Inner, Some(nameToAttr("f1_fk3") < nameToAttr("d3_pk1")))
.join(d2, Inner, Some(nameToAttr("f1_fk2") < nameToAttr("d2_pk1")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") < nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, d3, f1, d2, s3): _*)
assertEqualPlans(query, expected)
}
@@ -565,13 +573,27 @@ class StarJoinReorderSuite extends PlanTest with
StatsEstimationTestBase {
.join(d3, Inner, Some(nameToAttr("f1_fk3") === nameToAttr("d3_pk1")))
.join(d2, Inner, Some(nameToAttr("f1_fk2") === nameToAttr("d2_pk1")))
.join(s3, Inner, Some(nameToAttr("d3_fk1") === nameToAttr("s3_pk1")))
+ .select(outputsOf(d1, d3, f1, d2, s3): _*)
assertEqualPlans(query, expected)
}
- private def assertEqualPlans( plan1: LogicalPlan, plan2: LogicalPlan): Unit
= {
- val optimized = Optimize.execute(plan1.analyze)
+ private def assertEqualPlans(plan1: LogicalPlan, plan2: LogicalPlan): Unit =
{
+ val analyzed = plan1.analyze
+ val optimized = Optimize.execute(analyzed)
val expected = plan2.analyze
+
+ assert(equivalentOutput(analyzed, expected)) // if this fails, the
expected itself is incorrect
+ assert(equivalentOutput(analyzed, optimized))
+
compareJoinOrder(optimized, expected)
}
+
+ private def outputsOf(plans: LogicalPlan*): Seq[Attribute] = {
+ plans.map(_.output).reduce(_ ++ _)
+ }
+
+ private def equivalentOutput(plan1: LogicalPlan, plan2: LogicalPlan):
Boolean = {
+ normalizeExprIds(plan1).output == normalizeExprIds(plan2).output
+ }
}
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
b/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
index aa2162c9d2cda..91445c8d96d85 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
@@ -895,4 +895,18 @@ class JoinSuite extends QueryTest with SharedSQLContext {
checkAnswer(res, Row(0, 0, 0))
}
}
+
+ test("SPARK-26352: join reordering should not change the order of columns") {
+ withTable("tab1", "tab2", "tab3") {
+ spark.sql("select 1 as x, 100 as y").write.saveAsTable("tab1")
+ spark.sql("select 42 as i, 200 as j").write.saveAsTable("tab2")
+ spark.sql("select 1 as a, 42 as b").write.saveAsTable("tab3")
+
+ val df = spark.sql("""
+ with tmp as (select * from tab1 cross join tab2)
+ select * from tmp join tab3 on a = x and b = i
+ """)
+ checkAnswer(df, Row(1, 100, 42, 200, 1, 42))
+ }
+ }
}
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> join reordering should not change the order of output attributes
> ----------------------------------------------------------------
>
> Key: SPARK-26352
> URL: https://issues.apache.org/jira/browse/SPARK-26352
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.3.0, 2.4.0
> Reporter: Kris Mok
> Priority: Major
>
> The optimizer rule {{org.apache.spark.sql.catalyst.optimizer.ReorderJoin}}
> performs join reordering on inner joins. This was introduced from SPARK-12032
> in 2015-12.
> After it had reordered the joins, though, it didn't check whether or not the
> column order (in terms of the {{output}} attribute list) is still the same as
> before. Thus, it's possible to have a mismatch between the reordered column
> order vs the schema that a DataFrame thinks it has.
> This can be demonstrated with the example:
> {code:none}
> spark.sql("create table table_a (x int, y int) using parquet")
> spark.sql("create table table_b (i int, j int) using parquet")
> spark.sql("create table table_c (a int, b int) using parquet")
> val df = spark.sql("with df1 as (select * from table_a cross join table_b)
> select * from df1 join table_c on a = x and b = i")
> {code}
> here's what the DataFrame thinks:
> {code:none}
> scala> df.printSchema
> root
> |-- x: integer (nullable = true)
> |-- y: integer (nullable = true)
> |-- i: integer (nullable = true)
> |-- j: integer (nullable = true)
> |-- a: integer (nullable = true)
> |-- b: integer (nullable = true)
> {code}
> here's what the optimized plan thinks, after join reordering:
> {code:none}
> scala> df.queryExecution.optimizedPlan.output.foreach(a => println(s"|--
> ${a.name}: ${a.dataType.typeName}"))
> |-- x: integer
> |-- y: integer
> |-- a: integer
> |-- b: integer
> |-- i: integer
> |-- j: integer
> {code}
> If we exclude the {{ReorderJoin}} rule (using Spark 2.4's optimizer rule
> exclusion feature), it's back to normal:
> {code:none}
> scala> spark.conf.set("spark.sql.optimizer.excludedRules",
> "org.apache.spark.sql.catalyst.optimizer.ReorderJoin")
> scala> val df = spark.sql("with df1 as (select * from table_a cross join
> table_b) select * from df1 join table_c on a = x and b = i")
> df: org.apache.spark.sql.DataFrame = [x: int, y: int ... 4 more fields]
> scala> df.queryExecution.optimizedPlan.output.foreach(a => println(s"|--
> ${a.name}: ${a.dataType.typeName}"))
> |-- x: integer
> |-- y: integer
> |-- i: integer
> |-- j: integer
> |-- a: integer
> |-- b: integer
> {code}
> Note that this column ordering problem leads to data corruption, and can
> manifest itself in various symptoms:
> * Silently corrupting data, if the reordered columns happen to either have
> matching types or have sufficiently-compatible types (e.g. all fixed length
> primitive types are considered as "sufficiently compatible" in an UnsafeRow),
> then only the resulting data is going to be wrong but it might not trigger
> any alarms immediately. Or
> * Weird Java-level exceptions like {{java.lang.NegativeArraySizeException}},
> or even SIGSEGVs.
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