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https://issues.apache.org/jira/browse/HIVE-19937?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16553279#comment-16553279
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Misha Dmitriev commented on HIVE-19937:
---------------------------------------
The last patch looks good to me.
The only slight concern that I got from looking at it once again is the
following: in one or two places you switched from passing around Strings to
passing around Paths, and subsequently switched some HashMap(s)<String,
Something> to HashMap<Path, Something>. Note that a lookup in a map where keys
are complex objects is slower, because Path.equals(Path) is slower than
String.equals(String) - it may involve comparison of many strings, etc. I
haven't seen any reports on Hive CPU performance problems, and I hope this code
is not on a critical path, and/or that GC-related savings would offset the
potential hashmap lookup slowdown... but anyway, I guess it's worth remembering
about this.
> Intern fields in MapWork on deserialization
> -------------------------------------------
>
> Key: HIVE-19937
> URL: https://issues.apache.org/jira/browse/HIVE-19937
> Project: Hive
> Issue Type: Improvement
> Components: Spark
> Reporter: Sahil Takiar
> Assignee: Sahil Takiar
> Priority: Major
> Attachments: HIVE-19937.1.patch, HIVE-19937.2.patch,
> HIVE-19937.3.patch, HIVE-19937.4.patch, HIVE-19937.5.patch,
> post-patch-report.html, report.html
>
>
> When fixing HIVE-16395, we decided that each new Spark task should clone the
> {{JobConf}} object to prevent any {{ConcurrentModificationException}} from
> being thrown. However, setting this variable comes at a cost of storing a
> duplicate {{JobConf}} object for each Spark task. These objects can take up a
> significant amount of memory, we should intern them so that Spark tasks
> running in the same JVM don't store duplicate copies.
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