Mailing-List: contact mapreduce-dev-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: mapreduce-dev@hadoop.apache.org
Message-ID: <2782387.147291277957510377.JavaMail.jira@thor>
Date: Thu, 1 Jul 2010 00:11:50 -0400 (EDT)
From: "Rajesh Balamohan (JIRA)" <jira@apache.org>
To: mapreduce-dev@hadoop.apache.org
Subject: [jira] Created: (MAPREDUCE-1904) Reducing locking contention in
 TaskTracker.MapOutputServlet's LocalDirAllocator
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit

Reducing locking contention in TaskTracker.MapOutputServlet's LocalDirAllocator
-------------------------------------------------------------------------------

                 Key: MAPREDUCE-1904
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1904
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: tasktracker
    Affects Versions: 0.20.1
            Reporter: Rajesh Balamohan


While profiling tasktracker with Sort benchmark, it was observed that threads block on LocalDirAllocator.getLocalPathToRead() in order to get the index file and temporary map output file.

As LocalDirAllocator is tied up with ServetContext,  only one instance would be available per tasktracker httpserver.  Given the jobid & mapid, LocalDirAllocator retrieves index file path and temporary map output file path. getLocalPathToRead() is internally synchronized.

Introducing a LRUCache for this lookup reduces the contention heavily (LRUCache with key =jobid +mapid and value=PATH to the file). Size of the LRUCache can be varied based on the environment and I observed a throughput improvement in the order of 4-7% with the introduction of LRUCache.

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