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https://issues.apache.org/jira/browse/SPARK-26705?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hyukjin Kwon updated SPARK-26705:
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Priority: Major (was: Critical)
> UnsafeHashedRelation changed after broadcasted
> ----------------------------------------------
>
> Key: SPARK-26705
> URL: https://issues.apache.org/jira/browse/SPARK-26705
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.2.1
> Environment: spark:2.2.1
> jdk:
> java version "1.8.0_112"
> Java(TM) SE Runtime Environment (build 1.8.0_112-b15)
> Java HotSpot(TM) 64-Bit Server VM (build 25.112-b15, mixed mode)
> Reporter: Lijia Liu
> Priority: Major
>
> When Spark SQL execute a broadcast join, it will convert small table into
> UnsafeHashedRelation. But, in our cluster, I find that the
> UnsafeHashedRelation may changed after been broadcasted.
> The broadcasting process is divided into the following steps:
> 1. Collect the small table data to Array[InternalRow].
> (BroadcastExchangeExec.scala)
> 2. Transform the Array[InternalRow] to UnsafeHashedRelation object,
> UnsafeHashedRelation use a BytesToBytesMap to store
> data.(BroadcastExchangeExec.scala)
> 3. Use UnsafeHashedRelation.write function to serialize the object to byte
> stream.(HashedRelation.scala)
> 4. Use UnsafeHashedRelation.read function to deserialize the byte stream to
> UnsafeHashedRelation object.(HashedRelation.scala)
> I found that sometimes the BytesToBytesMap in UnsafeHashedRelation after
> deserialization is different from the one in UnsafeHashedRelation before
> serialization. For example, the number of keys become smaller.
> In our cluster, I will judge the BytesToBytesMap' key size and value size in
> UnsafeHashedRelation.read function to prevent incorrect result. But, I didn't
> found the real reason for this bug.
> The job witch occurred error has some peculiarities:
> 1. the broadcasted table is very big.
> 2. It's not a stable recurrence.
> 3. There are many tables has being broadcasted in the job.
> 4. Driver's memory pressure is high.
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