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From "Bryan Cutler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-22147) BlockId.hashCode allocates a StringBuilder/String on each call
Date Fri, 03 Nov 2017 15:33:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-22147?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16237775#comment-16237775
] 

Bryan Cutler commented on SPARK-22147:
--------------------------------------

Sorry, I linked the above PR to this JIRA accidentally

> BlockId.hashCode allocates a StringBuilder/String on each call
> --------------------------------------------------------------
>
>                 Key: SPARK-22147
>                 URL: https://issues.apache.org/jira/browse/SPARK-22147
>             Project: Spark
>          Issue Type: Improvement
>          Components: Block Manager
>    Affects Versions: 2.2.0
>            Reporter: Sergei Lebedev
>            Assignee: Sergei Lebedev
>            Priority: Minor
>             Fix For: 2.3.0
>
>
> The base class {{BlockId}} [defines|https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/storage/BlockId.scala#L44]
{{hashCode}} and {{equals}} for all its subclasses in terms of {{name}}. This makes the definitions
of different ID types [very concise|https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/storage/BlockId.scala#L52].
The downside, however, is redundant allocations. While I don't think this could be the major
issue, it is still a bit disappointing to increase GC pressure on the driver for nothing.
For our machine learning workloads, we've seen as much as 10% of all allocations on the driver
coming from {{BlockId.hashCode}} calls done for [BlockManagerMasterEndpoint.blockLocations|https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala#L54].



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