[ https://issues.apache.org/jira/browse/HDFS-4253?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Andy Isaacson updated HDFS-4253: -------------------------------- Attachment: hdfs4253-2.txt Avoid extra a.equals(b) by checking {{aIsLocal && bIsLocal}} instead. On average for a given sort this will result in fewer calls to {{.equals()}}. > block replica reads get hot-spots due to NetworkTopology#pseudoSortByDistance > ----------------------------------------------------------------------------- > > Key: HDFS-4253 > URL: https://issues.apache.org/jira/browse/HDFS-4253 > Project: Hadoop HDFS > Issue Type: Bug > Affects Versions: 3.0.0, 2.0.2-alpha > Reporter: Andy Isaacson > Assignee: Andy Isaacson > Attachments: hdfs4253-1.txt, hdfs4253-2.txt, hdfs4253.txt > > > When many nodes (10) read from the same block simultaneously, we get > asymmetric distribution of read load. This can result in slow block reads > when one replica is serving most of the readers and the other replicas are > idle. The busy DN bottlenecks on its network link. > This is especially visible with large block sizes and high replica counts (I > reproduced the problem with {{-Ddfs.block.size=4294967296}} and replication > 5), but the same behavior happens on a small scale with normal-sized blocks > and replication=3. > The root of the problem is in {{NetworkTopology#pseudoSortByDistance}} which > explicitly does not try to spread traffic among replicas in a given rack -- > it only randomizes usage for off-rack replicas. -- 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