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https://issues.apache.org/jira/browse/HIVE-19668?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Misha Dmitriev updated HIVE-19668:
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Status: Patch Available (was: In Progress)
The previous patch may or may not have been applied, thus I've just updated my
local git repo clone and generated a new patch file.
> Over 30% of the heap wasted by duplicate org.antlr.runtime.CommonToken's and
> duplicate strings
> ----------------------------------------------------------------------------------------------
>
> Key: HIVE-19668
> URL: https://issues.apache.org/jira/browse/HIVE-19668
> Project: Hive
> Issue Type: Improvement
> Components: HiveServer2
> Affects Versions: 3.0.0
> Reporter: Misha Dmitriev
> Assignee: Misha Dmitriev
> Priority: Major
> Attachments: HIVE-19668.01.patch, HIVE-19668.02.patch,
> HIVE-19668.03.patch, HIVE-19668.04.patch, image-2018-05-22-17-41-39-572.png
>
>
> I've recently analyzed a HS2 heap dump, obtained when there was a huge memory
> spike during compilation of some big query. The analysis was done with jxray
> ([www.jxray.com).|http://www.jxray.com)./] It turns out that more than 90% of
> the 20G heap was used by data structures associated with query parsing
> ({{org.apache.hadoop.hive.ql.parse.QBExpr}}). There are probably multiple
> opportunities for optimizations here. One of them is to stop the code from
> creating duplicate instances of {{org.antlr.runtime.CommonToken}} class. See
> a sample of these objects in the attached image:
> !image-2018-05-22-17-41-39-572.png|width=879,height=399!
> Looks like these particular {{CommonToken}} objects are constants, that don't
> change once created. I see some code, e.g. in
> {{org.apache.hadoop.hive.ql.parse.CalcitePlanner}}, where such objects are
> apparently repeatedly created with e.g. {{new
> CommonToken(HiveParser.TOK_INSERT, "TOK_INSERT")}} If these 33 token kinds
> are instead created once and reused, we will save more than 1/10th of the
> heap in this scenario. Plus, since these objects are small but very numerous,
> getting rid of them will remove a gread deal of pressure from the GC.
> Another source of waste are duplicate strings, that collectively waste 26.1%
> of memory. Some of them come from CommonToken objects that have the same text
> (i.e. for multiple CommonToken objects the contents of their 'text' Strings
> are the same, but each has its own copy of that String). Other duplicate
> strings come from other sources, that are easy enough to fix by adding
> String.intern() calls.
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