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https://issues.apache.org/jira/browse/HDDS-10382?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated HDDS-10382:
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Labels: pull-request-available (was: )
> Optimize Netty memory allocation by avoiding zero assignment in Java 9+
> -----------------------------------------------------------------------
>
> Key: HDDS-10382
> URL: https://issues.apache.org/jira/browse/HDDS-10382
> Project: Apache Ozone
> Issue Type: Improvement
> Reporter: Duong
> Assignee: Sarveksha Yeshavantha Raju
> Priority: Major
> Labels: pull-request-available
> Attachments: netty_bytebuf_allocation.png
>
>
> Add "-Dorg.apache.ratis.thirdparty.io.netty.tryReflectionSetAccessible=true"
> to the ozone script to allow Netty unsafe memory allocation.
> According to Netty
> [doc|https://netty.io/wiki/using-as-a-generic-library.html].
> {quote}When a new {{java.nio.ByteBuffer}} is allocated, its content is filled
> with zeroes. This "zeroing" consumes CPU cycles and memory bandwidth.
> Normally, the buffer is then immediately filled from some data source, so the
> zeroing did no good.
> {quote}
> And Netty has an optimization to avoid this zero assignment, its enablement
> is controlled by a flag: PlatformDependent.USE_DIRECT_BUFFER_NO_CLEANER. When
> this is enabled netty does the following to allocate a DirectByteBuffer:
> 1. Call "Unsafe.allocateMemory" to allocate the direct memory. This returns
> an address of the allocated buffer.
> 2. Use reflection to call a private constructor "DirectByteBuffer(long addr,
> int cap)" to create the DirectByteBuffer objects. This avoids zeroing the
> created buffer, as opposed to the public path "DirectByteBuffer(int cap)".
> However, the flag USE_DIRECT_BUFFER_NO_CLEANER is disabled by default in Java
> 9+ because the reflection in step #2 is disabled by default in Java 9+. This
> is controlled by a flag "io.netty.tryReflectionSetAccessible".
> The result is today, the zeroing takes a large portion of Netty allocation
> when Ozone runs on Java 9+.
> !netty_bytebuf_allocation.png|width=695,height=177!
> Setting the flag
> "-Dorg.apache.ratis.thirdparty.io.netty.tryReflectionSetAccessible=true"
> helps Netty leverage the Unsafe allocation and avoid the zeroing cost.
> Setting "io.netty.tryReflectionSetAccessible" is a common practice in other
> distributed systems, such as HBase, Spark... see:
> [https://github.com/search?q=io.netty.tryReflectionSetAccessible&type=code]
> A good side-effect of using Netty unsafe allocation is that the used direct
> memory is exposed as a metric, see HDDS-9070.
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