[MAPREDUCE-1266] Allow heartbeat interval smaller than 3 seconds for tiny clusters

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Duplicate
• Affects Version/s: 0.22.0
• Component/s: jobtracker, task, tasktracker
• Assignee: Unassigned
• Reporter: Todd Lipcon
• Created: 04/Dec/09 22:32
• Updated: 10/May/11 23:02
• Resolved: 10/May/11 23:02

Description

For small clusters, the heartbeat interval has a large effect on job latency. This is especially true on pseudo-distributed or other "tiny" (<5 nodes) clusters. It's not a big deal for production, but new users would have a happier first experience if Hadoop seemed snappier.

I'd like to change the minimum heartbeat interval from 3.0 seconds to perhaps 0.5 seconds (but have it governed by an undocumented config parameter in case people don't like this change). The cluster size-based ramp up of interval will maintain the current scalable behavior for large clusters with no negative effect.