hadoop-common-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Konstantin Boudnik (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-5734) HDFS architecture documentation describes outdated placement policy
Date Fri, 24 Apr 2009 00:53:30 GMT
HDFS architecture documentation describes outdated placement policy
-------------------------------------------------------------------

                 Key: HADOOP-5734
                 URL: https://issues.apache.org/jira/browse/HADOOP-5734
             Project: Hadoop Core
          Issue Type: Bug
          Components: documentation
    Affects Versions: 0.20.0
            Reporter: Konstantin Boudnik
            Priority: Minor


The "Replica Placement: The First Baby Steps" section of HDFS architecture document states:

"...
For the common case, when the replication factor is three, HDFS's placement policy is to put
one replica on one node in the local rack, another on a different node in the local rack,
and the last on a different node in a different rack. This policy cuts the inter-rack write
traffic which generally improves write performance.
..."

However, according to the ReplicationTargetChooser.chooseTarger()'s code the actual logic
is to put the second replica on a different rack as well as the third replica. So you have
two replicas located on a different nodes of remote rack and one (initial replica) on the
local rack's node. Thus, the sentence should say something like this:

"For the common case, when the replication factor is three, HDFS's placement policy is to
put one replica on one node in the local rack, another on a node in a different (remote) rack,
and the last on a different node in the same remote rack. This policy cuts the inter-rack
write traffic which generally improves write performance."


-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


Mime
View raw message