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Date: Mon, 26 Jun 2017 15:19:00 +0000 (UTC)
From: "Thomas (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Message-ID: <JIRA.13080545.1497658171000.105472.1498490340272@Atlassian.JIRA>
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Subject: [jira] [Commented] (HADOOP-14535) Support for random access and
 seek of block blobs
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archived-at: Mon, 26 Jun 2017 15:19:05 -0000


    [ https://issues.apache.org/jira/browse/HADOOP-14535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16063246#comment-16063246 ] 

Thomas commented on HADOOP-14535:
---------------------------------

Thanks for the feedback.  I will do the following and resubmit the patch in a few days:

1) Add logic so reverse seek followed by sequential read performs very well.  I will add internal buffering and remove the dependency on BufferedFSInputStream so the read buffer can grow back to the "fs.azure.read.request.size" (default 4 MB) after a reverse seek.

2) Add tests to ensure functional and performance coverage of seek, read, and skip.

3) If required for testing, I will add metrics/instrumentation.

> 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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