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authorgatorsmile <gatorsmile@gmail.com>2016-07-11 16:21:13 +0800
committerWenchen Fan <wenchen@databricks.com>2016-07-11 16:21:13 +0800
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[SPARK-16355][SPARK-16354][SQL] Fix Bugs When LIMIT/TABLESAMPLE is Non-foldable, 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 negative LIMIT/TABLESAMPLE, we should issue exceptions. Negative values could break the implementation 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. **Issue 3:** Spark SQL follows the restriction of LIMIT clause in Hive. The argument to the LIMIT clause must evaluate to a constant value. It can be a numeric literal, or another kind of numeric expression involving operators, casts, and function return values. You cannot refer to a column or use a subquery. Currently, we do not detect whether the expression in LIMIT clause is foldable or not. If non-foldable, we might issue a strange error message. For example, ```SQL SELECT * FROM testData LIMIT rand() > 0.2 ``` Then, a misleading error message is issued, like ``` assertion failed: No plan for GlobalLimit (_nondeterministic#203 > 0.2) +- Project [key#11, value#12, rand(-1441968339187861415) AS _nondeterministic#203] +- LocalLimit (_nondeterministic#202 > 0.2) +- Project [key#11, value#12, rand(-1308350387169017676) AS _nondeterministic#202] +- LogicalRDD [key#11, value#12] java.lang.AssertionError: assertion failed: No plan for GlobalLimit (_nondeterministic#203 > 0.2) +- Project [key#11, value#12, rand(-1441968339187861415) AS _nondeterministic#203] +- LocalLimit (_nondeterministic#202 > 0.2) +- Project [key#11, value#12, rand(-1308350387169017676) AS _nondeterministic#202] +- LogicalRDD [key#11, value#12] ``` This PR detects it and then issues a meaningful error message. #### How was this patch tested? Added test cases. Author: gatorsmile <gatorsmile@gmail.com> Closes #14034 from gatorsmile/limit.
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