hadoop-common-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-6502) DistributedFileSystem#listStatus is very slow when listing a directory with a size of 1300
Date Fri, 22 Jan 2010 01:24:54 GMT
DistributedFileSystem#listStatus is very slow when listing a directory with a size of 1300
------------------------------------------------------------------------------------------

                 Key: HADOOP-6502
                 URL: https://issues.apache.org/jira/browse/HADOOP-6502
             Project: Hadoop Common
          Issue Type: Bug
          Components: util
    Affects Versions: 0.20.0
            Reporter: Hairong Kuang
            Priority: Critical
             Fix For: 0.20.2, 0.21.0, 0.22.0


When listing a directory of around 1300 children, it takes hundreds of milliseconds. It turns
out the slowdowness is caused by the change made by HADOOP-4187. The return value of listStatus
is an array of FileStatus. When serializing each element of the array, ReflectionUtils#newInstance(Class<T>,
Configuration) is called and then calls setConf, which calls setJobConf. SetJobConf checks
if JobConf is on the class path by calling Configuration#getClassByName. Even though Configuration#getClassByName
tries to optimize the lookup using a cached map, but since JobConf is not in the class path,
so it is not in the cache. Every checkup ends up calling Class.ForName which is very expensive.
Deserializing an array of 1300 entries requires calling of Class#ForName 1300 times!

-- 
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