Rajesh Balamohan created HADOOP-14478:
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Summary: 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
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 apart of this
JIRA.
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