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https://issues.apache.org/jira/browse/HADOOP-14478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16037914#comment-16037914
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Rajesh Balamohan commented on HADOOP-14478:
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[~liuml07] - Perf improvement would be observed when {{BlobInputStream}} is
fixed. Thanks for creating HADOOP-14490.
> Optimize NativeAzureFsInputStream for positional reads
> ------------------------------------------------------
>
> Key: HADOOP-14478
> URL: https://issues.apache.org/jira/browse/HADOOP-14478
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs/azure
> Reporter: Rajesh Balamohan
> Assignee: Rajesh Balamohan
> Fix For: 2.9.0, 3.0.0-alpha4
>
> Attachments: HADOOP-14478.001.patch, HADOOP-14478.002.patch,
> HADOOP-14478.003.patch
>
>
> Azure's {{BlobbInputStream}} internally buffers 4 MB of data irrespective of
> the data length requested for. This would be beneficial for sequential reads.
> However, for positional reads (seek to specific location, read x number of
> bytes, seek back to original location) this may not be beneficial and might
> even download lot more data which are not used later.
> It would be good to override {{readFully(long position, byte[] buffer, int
> offset, int length)}} for {{NativeAzureFsInputStream}} and make use of
> {{mark(readLimit)}} as a hint to Azure's BlobInputStream.
> BlobInputStream reference:
> https://github.com/Azure/azure-storage-java/blob/master/microsoft-azure-storage/src/com/microsoft/azure/storage/blob/BlobInputStream.java#L448
> BlobInputStream can consider this as a hint later to determine the amount of
> data to be read ahead. Changes to BlobInputStream would not be addressed in
> this JIRA.
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