HDFS Devs, We propose merging the HDFS-6581 development branch to trunk.
The work adds support to write to HDFS blocks in memory. The target use case covers applications writing relatively small, intermediate data sets with low latency. We introduce a new CreateFlag for the existing CreateFile API. HDFS will subsequently attempt to place replicas of file blocks in local memory with disk writes occurring off the hot path. The current design is a simplification of original ideas from Sanjay Radia on HDFS-5851. Key goals of the feature were minimal API changes to reduce application burden and best effort data durability. The feature is optional and requires appropriate DN configuration from administrators. Design doc: https://issues.apache.org/jira/secure/attachment/12661926/HDFSWriteableReplicasInMemory.pdf Test plan: https://issues.apache.org/jira/secure/attachment/12669452/Test-Plan-for-HDFS-6581-Memory-Storage.pdf There are 28 resolved sub-tasks under HDFS-6581, 3 open tasks for tests+Jenkins issues and 7 open subtasks tracking planned improvements. The latest merge patch is 3300 lines of changed code of which 1300 lines is new and updated tests. Merging the branch to trunk will allow HDFS applications to start evaluating the feature. We will continue work on documentation, performance tuning and metrics in parallel with the vote and post-merge. Contributors to design and code include Xiaoyu Yao, Sanjay Radia, Jitendra Pandey, Tassapol Athiapinya, Gopal V, Bikas Saha, Vikram Dixit, Suresh Srinivas and Chris Nauroth. Thanks to Haohui Mai, Colin Patrick McCabe, Andrew Wang, Todd Lipcon, Eric Baldeschwieler and Vinayakumar B for providing useful feedback on HDFS-6581, HDFS-5851 and sub-tasks. The vote runs for the usual 7 days and will expire at 12am PDT on Sep 30. Here is my +1 for the merge. Regards, Arpit -- CONFIDENTIALITY NOTICE NOTICE: This message is intended for the use of the individual or entity to which it is addressed and may contain information that is confidential, privileged and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any printing, copying, dissemination, distribution, disclosure or forwarding of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and delete it from your system. Thank You.
