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https://issues.apache.org/jira/browse/SPARK-13299?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen resolved SPARK-13299.
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Resolution: Not A Problem
Unless your DataFrame has a defined ordering, I don't think you'd expect the
first N to be a particular set. First w.r.t. what? it will be some default
ordering that's a function of however it was partitioned and read
> DataFrame limit operation is not consistent
> -------------------------------------------
>
> Key: SPARK-13299
> URL: https://issues.apache.org/jira/browse/SPARK-13299
> Project: Spark
> Issue Type: Bug
> Affects Versions: 1.3.1, 1.5.0, 1.5.1, 1.5.2, 1.6.0
> Reporter: Nazarii Balkovskyi
> Labels: SparkSQL, dataframe
> Attachments: SparkLimitIssue.png
>
>
> I faced to a problem with using limit method from DataFrame API.
> I try to get first 999 records from the AVRO source which contains about 3.5K
> records.
> {code:java}
> DataFrame df = sqlContext.load(inputSource, "com.databricks.spark.avro");
> df = df.limit(999);
> {code}
> Then after saving operation I get the rows not in the same order as in input
> data set. Sometimes it gives me proper order but usually not.
> {code:java}
> df.save(filepathToSave, "com.databricks.spark.avro", SaveMode.ErrorIfExists);
> {code}
> Here you can see Spark plan (maybe it can help to figure out the cause of the
> issue):
> {code}
> == Parsed Logical Plan ==
> Limit 999
> Relation[mobileNumber#0L,tariff#1,debit#2]
> AvroRelation(hdfs://<server_name>:8020/user/hdfs/dataset.avro,None,0)
> == Analyzed Logical Plan ==
> mobileNumber: bigint, tariff: string, debit: float
> Limit 999
> Relation[mobileNumber#0L,tariff#1,debit#2]
> AvroRelation(hdfs://<server_name>:8020/user/hdfs/dataset.avro,None,0)
> == Optimized Logical Plan ==
> Limit 999
> Relation[mobileNumber#0L,tariff#1,debit#2]
> AvroRelation(hdfs://<server_name>:8020/user/hdfs/dataset.avro,None,0)
> == Physical Plan ==
> Limit 999
> Scan
> AvroRelation(hdfs://<server_name>:8020/user/hdfs/dataset.avro,None,0)[mobileNumber#0L,tariff#1,debit#2]
> Code Generation: true
> {code}
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