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Allen Wittenauer updated HDFS-4253: ----------------------------------- Attachment: (was: HDFS-5253.06.patch) > 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: HDFS-4253.06.patch, hdfs4253-1.txt, hdfs4253-2.txt, > hdfs4253-3.txt, hdfs4253-4.txt, hdfs4253-5.txt, hdfs4253-6.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 was sent by Atlassian JIRA (v6.3.4#6332)