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From "Eric Hanson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10809) hadoop-azure: page blob support
Date Tue, 29 Jul 2014 20:24:42 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14078301#comment-14078301
] 

Eric Hanson commented on HADOOP-10809:
--------------------------------------

I mean "let" you know. I guess that was a Freudian slip :-).

> hadoop-azure: page blob support
> -------------------------------
>
>                 Key: HADOOP-10809
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10809
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: tools
>            Reporter: Mike Liddell
>            Assignee: Mike Liddell
>         Attachments: HADOOP-10809.1.patch
>
>
> Azure Blob Storage provides two flavors: block-blobs and page-blobs.  Block-blobs are
the general purpose kind that support convenient APIs and are the basis for the Azure Filesystem
for Hadoop (see HADOOP-9629).
> Page-blobs use the same namespace as block-blobs but provide a different low-level feature
set.  Most importantly, page-blobs can cope with an effectively infinite number of small accesses
whereas block-blobs can only tolerate 50K appends before relatively manual rewriting of the
data is necessary.  A simple analogy is that page-blobs are like a regular disk and the basic
API is like a low-level device driver.
> See http://msdn.microsoft.com/en-us/library/azure/ee691964.aspx for some introductory
material.
> The primary driving scenario for page-blob support is for HBase transaction log files
which require an access pattern of many small writes.  Additional scenarios can also be supported.
> Configuration:
> The Hadoop Filesystem abstraction needs a mechanism so that file-create can determine
whether to create a block- or page-blob.  To permit scenarios where application code doesn't
know about the details of azure storage we would like the configuration to be Aspect-style,
ie configured by the Administrator and transparent to the application. The current solution
is to use hadoop configuration to declare a list of page-blob folders -- Azure Filesystem
for Hadoop will create files in these folders using page-blob flavor.  The configuration key
is "fs.azure.page.blob.dir", and description can be found in AzureNativeFileSystemStore.java.
> Code changes:
> - refactor of basic Azure Filesystem code to use a general BlobWrapper and specialized
BlockBlobWrapper vs PageBlobWrapper
> - introduction of PageBlob support (read, write, etc)
> - miscellaneous changes such as umask handling, implementation of createNonRecursive(),
flush/hflush/hsync.
> - new unit tests.
> Credit for the primary patch: Dexter Bradshaw, Mostafa Elhemali, Eric Hanson, Mike Liddell.



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