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Posted to common-issues@hadoop.apache.org by "Rajesh Balamohan (JIRA)" <ji...@apache.org> on 2017/06/02 06:30:05 UTC
[jira] [Created] (HADOOP-14478) Optimize NativeAzureFsInputStream
for positional reads
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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