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https://issues.apache.org/jira/browse/SPARK-26352?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16719620#comment-16719620
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ASF GitHub Bot commented on SPARK-26352:
----------------------------------------
rednaxelafx opened a new pull request #23303: [SPARK-26352][SQL] ReorderJoin
should not change the order of columns
URL: https://github.com/apache/spark/pull/23303
## What changes were proposed in this pull request?
The optimizer rule `org.apache.spark.sql.catalyst.optimizer.ReorderJoin`
performs join reordering on inner joins. This was introduced from SPARK-12032
(https://github.com/apache/spark/pull/10073) 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:
```scala
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
""")
```
here's what the DataFrame thinks:
```
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)
```
here's what the optimized plan thinks, after join reordering:
```
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
```
If we exclude the `ReorderJoin` rule (using Spark 2.4's optimizer rule
exclusion feature), it's back to normal:
```
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
```
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.
## How was this patch tested?
Added new unit test in `JoinReorderSuite` and new end-to-end test in
`JoinSuite`.
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> ReorderJoin should not change the order of columns
> --------------------------------------------------
>
> 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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