This is a post by Constantine Peresypkin and David Gruzman.
Lately we were working on integrating Hadoop with OpenStack Swift. Hadoop doesn’t need an introduction neither does OpenStack. Swift is an object-storage system and the technology behind RackSpace cloud-files (and quite a few others like Korea Telecom object storage, Internap and etc…)
Before we go into details of Hadoop-Swift integration let’s get some relevant background:
- Hadoop already have integration with Amazon S3 and is widely used to crunch S3-stored data. http://wiki.apache.org/hadoop/AmazonS3
- NameNode is a known SPOF in Hadoop. If it can be avoided it would be nice.
- Current S3 integration stages all data as temporary files on local disk to S3. That’s because S3 needs to know content length in advance it is one of the required headers.
- Current S3 also suffers form 5GB max file limitation which is slightly annoying.
- Hadoop requires seek support which means that HTTP range support is required if it is run over an object-storage . S3 supports it.
- Append file support is optional for Hadoop, but it’s required for HBase. S3 doesn’t have any append support thus native integration can not use HBase over S3.
- While OpenStack Swift is compatible with S3, RackSpace CloudFiles is not. It is because RackSpace CloudFiles disables S3-compatibility layer in Swift. This prevents existing Swift users from integration with Hadoop.
- The only information that is available on Internet on Hadoop-Swift integration is that with using Apache Whirr! it should work. But for best of our knowledge it is relevant only to rolling out Block FileSystem on top of Swift not a Native FileSystem. In other words we haven’t found any solution on how to process data that is already stored in RackSpace CloudFiles without costly re-importing.
So instrumented with above information let’s examine what we got here:
- In general we instrumented Hadoop to run over Swift naively, without resorting to S3 compatibility layer. This means it works with CloudFiles which misses the S3-compatibility layer.
- CloudFiles client SDK doesn’t have support for HTTP range functionality. Hacked it to allow using HTTP range, this is a must for Hadoop to work.
- Removed the need for NameNode in similar way it is removed with S3 integration for Amazon.
- As opposed to S3 implementation we avoided staging files on local disk to and from CloudFiles/Swift. In other words data directly streamed to/from compute node RAM into CloudFiles/Swift.
- Though the data is still processed remotely. Extensive data shipping takes place between compute nodes and CloudFiles/Swift. As frequent readers of this blog know we are working on technology that will allow to run code snippets directly in Swift. Look here for more details: http://www.zerovm.com. As next step we plan to perform predicate-pushdown optimization to process most of data completely locally inside ZeroVM-enabled object-storage system.
- Support for native Swift large objects is planned also (something that’s absent in Amazon S3)
- We also working on append support for Swift (this could be easily done through Swift large object support which uses versioning) so even HBase will work on top of Swift, and this is not the case with S3 now.
- As it is the case with Hadoop S3, storing BigData in native format on Swift provides options for multi-site replication and CDN
I also added a question to Quora on this issue: http://www.quora.com/Is-it-possible-to-run-Hadoop-to-directly-process-data-stored-in-RackSpace-CloudFiles-Swift