[MAPREDUCE-4303] Look at using String.intern to dedupe some Strings

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 0.23.3, 2.0.0-alpha
• Component/s: applicationmaster
• Assignee: Unassigned
• Reporter: Robert Joseph Evans
• Created: 01/Jun/12 19:19
• Updated: 24/Oct/12 14:03
• Resolved: 24/Oct/12 14:03

Description

MAPREDUCE-4301 fixes one issue with too many duplicate strings, but there are other places where it is not as simple to remove the duplicates. In these cases the source of the strings is an incoming RPC call or from parsing and reading in a file. The only real way to dedupe these is to either use String.intern() which if not used properly could result in the permgen space being filled up, or by playing games with our own cache, and trying to do the same sort of thing as String.intern, but in the heap.

The following are some that I saw lots of duplicate strings that we should look at doing something about.

TaskAttemptStatusUpdateEvent$TaskAttemptState.stateString
MapTaskAttemptImpl.diagnostics
The keys to Counters.groups
GenericGroup.displayName
The keys to GenericGroup.counters
and GenericCounter.displayName

Issue Links

• is duplicated by: MAPREDUCE-4229 Counter names' memory usage can be decreased by interning