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https://issues.apache.org/jira/browse/HBASE-30391?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated HBASE-30391:
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Labels: pull-request-available (was: )
> Reduce array copying when expanding ByteArrayOutputStream
> ---------------------------------------------------------
>
> Key: HBASE-30391
> URL: https://issues.apache.org/jira/browse/HBASE-30391
> Project: HBase
> Issue Type: Improvement
> Components: HFile
> Affects Versions: 2.4.11
> Reporter: huginn
> Priority: Minor
> Labels: pull-request-available
>
> ## What happens
> The custom ByteArrayOutputStream copies the entire backing array when it
> expands, including unused capacity.
> ## When it happens
> This occurs when a write exceeds the current buffer capacity and the stream
> allocates a larger backing array.
> ## Impact
> The unnecessary copy increases CPU work and temporary heap memory traffic,
> especially for buffers whose logical content is much smaller than their
> capacity.
> ## Root cause
> In ByteArrayOutputStream.checkSizeAndGrow, the expansion path copies
> buf.length bytes even though only pos bytes contain valid stream data.
> ## Proposed fix
> Copy only the bytes already written to the stream (pos) when expanding the
> backing array. This preserves the stream contents while avoiding copies of
> unused capacity.
> ## Reproduction
> The behavior can be observed by writing data in increments that trigger
> buffer expansion and profiling the resulting array-copy work. Testing
> evidence will be added by the reporter.{color:red}着色文本{color}
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