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https://issues.apache.org/jira/browse/HADOOP-14535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16060926#comment-16060926
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Steve Loughran commented on HADOOP-14535:
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in HADOOP-14553 I've added a new test which can create a large file and then do
seeks around it. I'd like that test to be used as the regression test here.
> Support for random access and seek of block blobs
> -------------------------------------------------
>
> Key: HADOOP-14535
> URL: https://issues.apache.org/jira/browse/HADOOP-14535
> Project: Hadoop Common
> Issue Type: Improvement
> Components: fs/azure
> Reporter: Thomas
> Assignee: Thomas
> Attachments:
> 0001-Random-access-and-seek-imporvements-to-azure-file-system.patch,
> 0003-Random-access-and-seek-imporvements-to-azure-file-system.patch,
> 0004-Random-access-and-seek-imporvements-to-azure-file-system.patch
>
>
> This change adds a seek-able stream for reading block blobs to the wasb://
> file system.
> If seek() is not used or if only forward seek() is used, the behavior of
> read() is unchanged.
> That is, the stream is optimized for sequential reads by reading chunks (over
> the network) in
> the size specified by "fs.azure.read.request.size" (default is 4 megabytes).
> If reverse seek() is used, the behavior of read() changes in favor of reading
> the actual number
> of bytes requested in the call to read(), with some constraints. If the size
> requested is smaller
> than 16 kilobytes and cannot be satisfied by the internal buffer, the network
> read will be 16
> kilobytes. If the size requested is greater than 4 megabytes, it will be
> satisfied by sequential
> 4 megabyte reads over the network.
> This change improves the performance of FSInputStream.seek() by not closing
> and re-opening the
> stream, which for block blobs also involves a network operation to read the
> blob metadata. Now
> NativeAzureFsInputStream.seek() checks if the stream is seek-able and moves
> the read position.
> [^attachment-name.zip]
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