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.
