[jira] [Created] (HADOOP-13390) GC pressure of NetworkTopology.isAncestor call can be eliminated

["He Tianyi (JIRA)" <ji...@apache.org>]

He Tianyi created HADOOP-13390:
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             Summary: GC pressure of NetworkTopology.isAncestor call can be eliminated
                 Key: HADOOP-13390
                 URL: https://issues.apache.org/jira/browse/HADOOP-13390
             Project: Hadoop Common
          Issue Type: Improvement
          Components: net
    Affects Versions: 2.7.0, 2.6.0, 2.8.0
            Reporter: He Tianyi
            Priority: Minor


{{NetworkTopology.isAncestor}} is called in {{NetworkTopology.getLeaf}}, which is excessively used in block placement policies ({{chooseRandom}} for example).

Currently, the implementation calls {{getPath}} twice. And {{getPath}} performs string concatenation on the fly. On a busy NameNode, this introduces more GC pressure and CPU overhead for block allocation. 
Given that network location and node name does not generally change frequently, we can cache path as a properly of {{Node}} and update accordingly while network location or node name is changing.
Also, one of these {{getPath}} calls in {{getLeaf}} can be eliminated because we are expecting identical result in both calls.



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