[HADOOP-16641] RPC: Heavy contention on Configuration.getClassByNameOrNull

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: conf
• Labels: performance
• Assignee: Unassigned
• Reporter: Gopal Vijayaraghavan
• Created: 08/Oct/19 05:30
• Updated: 08/Oct/19 17:35

Description

https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java#L2589

        map = Collections.synchronizedMap(
          new WeakHashMap<String, WeakReference<Class<?>>>());

This synchronizes all lookups across the same class-loader across all threads & yields rpc threads.

When reading from HDFS with good locality, this fills up the contended lock profile with almost no other contributors to the locking - see llap-rpc-locks.svg