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https://issues.apache.org/jira/browse/SPARK-37593?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-37593:
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Assignee: (was: Apache Spark)
> Optimize HeapMemoryAllocator to avoid memory waste in humongous allocation
> when using G1GC
> ------------------------------------------------------------------------------------------
>
> Key: SPARK-37593
> URL: https://issues.apache.org/jira/browse/SPARK-37593
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core, SQL
> Affects Versions: 3.3.0
> Reporter: EdisonWang
> Priority: Minor
> Fix For: 3.3.0
>
>
> As we may know, a phenomenon called humongous allocations exists in G1GC when
> allocations that are larger than 50% of the region size.
> Spark's tungsten memory model usually tries to allocate memory by one `page`
> each time and allocated by long[pageSizeBytes/8] in
> HeapMemoryAllocator.allocate.
> Remember that java long array needs extra object header (usually 16 bytes in
> 64bit system), so the really bytes allocated is pageSize+16.
> Assume that the G1HeapRegionSize is 4M and pageSizeBytes is 4M as well. Since
> every time we need to allocate 4M+16byte memory, so two regions are used with
> one region only occupies 16byte. Then there are about 50% memory waste.
> It can happenes under different combinations of G1HeapRegionSize (varies from
> 1M to 32M) and pageSizeBytes (varies from 1M to 64M).
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