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Tomasz Nykiel updated HDFS-2477: -------------------------------- Attachment: reportDiff.patch > Optimize computing the diff between a block report and the namenode state. > -------------------------------------------------------------------------- > > Key: HDFS-2477 > URL: https://issues.apache.org/jira/browse/HDFS-2477 > Project: Hadoop HDFS > Issue Type: Sub-task > Components: name-node > Reporter: Tomasz Nykiel > Assignee: Tomasz Nykiel > Attachments: reportDiff.patch > > > When a block report is processed at the NN, the BlockManager.reportDiff > traverses all blocks contained in the report, and for each one block, which > is also present in the corresponding datanode descriptor, the block is moved > to the head of the list of the blocks in this datanode descriptor. > With HDFS-395 the huge majority of the blocks in the report, are also present > in the datanode descriptor, which means that almost every block in the report > will have to be moved to the head of the list. > Currently this operation is performed by DatanodeDescriptor.moveBlockToHead, > which removes a block from a list and then inserts it. In this process, we > call findDatanode several times (afair 6 times for each moveBlockToHead > call). findDatanode is relatively expensive, since it linearly goes through > the triplets to locate the given datanode. > With this patch, we do some memoization of findDatanode, so we can reclaim 2 > findDatanode calls. Our experiments show that this can improve the reportDiff > (which is executed under write lock) by around 15%. Currently with HDFS-395, > reportDiff is responsible for almost 100% of the block report processing time. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira