GitHub user gatorsmile opened a pull request:
https://github.com/apache/spark/pull/14034
[16355] [16354] [SQL] Fix Bugs When LIMIT/TABLESAMPLE is Zero or Negative
#### What changes were proposed in this pull request?
**Issue 1:** When a query containing LIMIT/TABLESAMPLE 0, the statistics
could be zero. Results are correct but it could cause a huge performance
regression. For example,
```Scala
Seq(("one", 1), ("two", 2), ("three", 3), ("four", 4)).toDF("k", "v")
.createOrReplaceTempView("test")
val df1 = spark.table("test")
val df2 = spark.table("test").limit(0)
val df = df1.join(df2, Seq("k"), "left")
```
The statistics of both `df` and `df2` are zero. The statistics values
should never be zero; otherwise `sizeInBytes` of `BinaryNode` will also be zero
(product of children). This PR is to increase it to `1` when the num of rows is
equal to 0.
**Issue 2:** When a query containing LIMIT/TABLESAMPLE is negative, we
should issue exceptions. Negative values could break the assumption of multiple
parts. For example, statistics calculation. Below is the example query.
```SQL
SELECT * FROM testData TABLESAMPLE (-1 rows)
SELECT * FROM testData LIMIT -1
```
This PR is to issue an appropriate exception in this case.
#### How was this patch tested?
Added test cases.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/gatorsmile/spark limit
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/14034.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #14034
----
commit 1255968908454bfb01b247567f796e10ca6e6d30
Author: gatorsmile <gatorsm...@gmail.com>
Date: 2016-07-03T05:46:44Z
fix
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