[MAPREDUCE-4752] Reduce MR AM memory usage through String Interning

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.3-alpha, 0.23.5
• Component/s: mrv2
• Target Version/s: 2.0.3-alpha, 0.23.5
• Assignee: Robert Joseph Evans
• Reporter: Robert Joseph Evans
• Created: 26/Oct/12 14:47
• Updated: 03/Sep/14 23:17
• Resolved: 31/Oct/12 15:03

Description

There are a lot of strings that are duplicates of one another in the AM. This comes from all of the PB events the come across the wire and also tasks heart-beating in through the umbilical. There are even several duplicates from Configuration. By "interning" all of these strings on the Heap I have been able to reduce the resting memory usage of the AM to be about 5KB per task attempt. With about half of this coming from counters. This results in a 5MB heap for a typical 1000 task job, or a 500MB heap for a 100,000 task attempt job. I think I could cut the size of the counters in half by completely rewriting how counters work in the AM and History Server, but I don't think it is worth it at this point.

I am still investigating what the memory usage of the AM is like when running very large jobs, and I will probably have a follow-up JIRA for reducing that memory usage as well.

Issue Links

• duplicates: HADOOP-9003 StringIntern not handling null correctly