[jira] [Created] (HADOOP-10809) hadoop-azure: page blob support

["Mike Liddell (JIRA)" <ji...@apache.org>]

Mike Liddell created HADOOP-10809:
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             Summary: 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


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 are more difficult to use but provide a different 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.  The simplest analogy is that page-blobs are like a normal filesystem (eg FAT) and the 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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