[ https://issues.apache.org/jira/browse/HDFS-4461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13568989#comment-13568989 ] Todd Lipcon commented on HDFS-4461: ----------------------------------- Looks like we can cut the memory usage in half again -- storing both the metafile path and the block file path is redundant, since you can always compute the block path from the meta path by chopping off the "_.meta" prefix. Suresh -- we routinely see users with millions of replicas per DN now that 48TB+ configurations have become commodity. Sure, we should also encourage users to use things like HAR to coalesce into larger blocks, but easy wins on DN memory usage are a no-brainer IMO. > DirectoryScanner: volume path prefix takes up memory for every block that is scanned > ------------------------------------------------------------------------------------- > > Key: HDFS-4461 > URL: https://issues.apache.org/jira/browse/HDFS-4461 > Project: Hadoop HDFS > Issue Type: Improvement > Affects Versions: 2.0.3-alpha > Reporter: Colin Patrick McCabe > Assignee: Colin Patrick McCabe > Priority: Minor > Attachments: HDFS-4461.002.patch, HDFS-4461.003.patch, memory-analysis.png > > > In the {{DirectoryScanner}}, we create a class {{ScanInfo}} for every block. This object contains two File objects-- one for the metadata file, and one for the block file. Since those File objects contain full paths, users who pick a lengthly path for their volume roots will end up using an extra N_blocks * path_prefix bytes per block scanned. We also don't really need to store File objects-- storing strings and then creating File objects as needed would be cheaper. This would be a nice efficiency improvement. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira