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https://issues.apache.org/jira/browse/SPARK-23697?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-23697:
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Assignee: Apache Spark
> Accumulators of Spark 1.x no longer work with Spark 2.x
> -------------------------------------------------------
>
> Key: SPARK-23697
> URL: https://issues.apache.org/jira/browse/SPARK-23697
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 2.2.0, 2.2.1, 2.3.0
> Environment: Spark 2.2.0
> Scala 2.11
> Reporter: Sergey Zhemzhitsky
> Assignee: Apache Spark
> Priority: Major
>
> I've noticed that accumulators of Spark 1.x no longer work with Spark 2.x
> failing with
> {code:java}
> java.lang.AssertionError: assertion failed: copyAndReset must return a zero
> value copy{code}
> It happens while serializing an accumulator
> [here|https://github.com/apache/spark/blob/4f5bad615b47d743b8932aea1071652293981604/core/src/main/scala/org/apache/spark/util/AccumulatorV2.scala#L165]
> {code:java}
> val copyAcc = copyAndReset()
> assert(copyAcc.isZero, "copyAndReset must return a zero value copy"){code}
> ... although copyAndReset returns zero-value copy for sure, just consider the
> accumulator below
> {code:java}
> val concatParam = new AccumulatorParam[jl.StringBuilder] {
> override def zero(initialValue: jl.StringBuilder): jl.StringBuilder = new
> jl.StringBuilder()
> override def addInPlace(r1: jl.StringBuilder, r2: jl.StringBuilder):
> jl.StringBuilder = r1.append(r2)
> }{code}
> So, Spark treats zero value as non-zero due to how
> [isZero|https://github.com/apache/spark/blob/4f5bad615b47d743b8932aea1071652293981604/core/src/main/scala/org/apache/spark/util/AccumulatorV2.scala#L489]
> is implemented in LegacyAccumulatorWrapper.
> {code:java}
> override def isZero: Boolean = _value == param.zero(initialValue){code}
> All this means that the values to be accumulated must implement equals and
> hashCode, otherwise isZero is very likely to always return false.
> So I'm wondering whether the assertion
> {code:java}
> assert(copyAcc.isZero, "copyAndReset must return a zero value copy"){code}
> is really necessary and whether it can be safely removed from there?
> If not - is it ok to just override writeReplace for LegacyAccumulatorWrapper
> to prevent such failures?
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