[HADOOP-14938] Configuration.updatingResource map should be initialized lazily

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.9.0, 3.0.0
• Hadoop Flags: Reviewed
• Assignee: Misha Dmitriev
• Reporter: Misha Dmitriev
• Created: 09/Oct/17 19:36
• Updated: 21/Jan/19 16:02
• Resolved: 16/Oct/17 23:55

Description

Using jxray (www.jxray.com), I've analyzed a heap dump of YARN RM running in a big cluster. The tool uncovered several inefficiencies in the RM memory. It turns out that one of the biggest sources of memory waste, responsible for almost 1/4 of used memory, is empty ConcurrentHashMap instances in org.apache.hadoop.conf.Configuration.updatingResource:

905,551K (24.0%): java.util.concurrent.ConcurrentHashMap: 22118 / 100% of empty 905,551K (24.0%)
↖org.apache.hadoop.conf.Configuration.updatingResource
↖{j.u.WeakHashMap}.keys
↖Java Static org.apache.hadoop.conf.Configuration.REGISTRY

That is, there are 22118 empty ConcurrentHashMaps here, and they collectively waste ~905MB of memory. This is caused by eager initialization of these maps. To address this problem, we should initialize them lazily.