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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