Kaibo Zhou created YARN-1226:
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Summary: ipv4 and ipv6 affect job data locality
Key: YARN-1226
URL: https://issues.apache.org/jira/browse/YARN-1226
Project: Hadoop YARN
Issue Type: Improvement
Components: capacityscheduler
Affects Versions: 2.1.0-beta, 2.0.0-alpha, 0.23.3
Reporter: Kaibo Zhou
Priority: Minor
When I run a mapreduce job which use TableInputFormat to scan a hbase table on
yarn cluser with 140+ nodes, I consistently get very low data locality
(capacity scheduler) around 0~10%.
Hbase and hadoop are integrated in the cluster with NodeManager, DataNode and
HRegionServer run on the same node.
The reason of low data locality is: most machines in the cluster uses IPV6, few
machines use IPV4. NodeManager use "InetAddress.getLocalHost().getHostName()
" to get the host name, but the return result of this function depends on IPV4
or IPV6, see "http://bugs.sun.com/view_bug.do?bug_id=7166687";.
On machines with ipv4, NodeManager get hostName as:
search042097.sqa.cm4.site.net
But on machines with ipv6, NodeManager get hostName as: search042097.sqa.cm4
if run with IPv6 disabled, -Djava.net.preferIPv4Stack=true, then returns
search042097.sqa.cm4.site.net.
For the mapred job which scan hbase table, the InputSplit contains node
locations of FQDN, e.g. search042097.sqa.cm4.site.net. Because in hbase, the
RegionServers' hostnames are allocated by HMaster. HMaster communicate with
RegionServers and get the region server's host name use java NIO:
clientChannel.socket().getInetAddress().getHostName().
Also see the startup log of region server:
13:06:21,200 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: Master
passed us hostname to use. Was=search042024.sqa.cm4,
Now=search042024.sqa.cm4.site.net
As you can see, most machines in the Yarn cluster with IPV6 get the short
hostname, but hbase always get the full hostname, so the Host cannot matched
(see RMContainerAllocator::assignToMap).This can lead to poor locality.
After I use java.net.preferIPv4Stack to force IPv4 in yarn, I get 70+% data
locality in the cluster.
Thanks,
Kaibo
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