[HIVE-22165] Synchronisation introduced by HIVE-14296 on SessionManager.closeSession causes high latency in a busy hive server

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.1.0, 2.3.2
• Fix Version/s: 4.0.0-alpha-1
• Component/s: HiveServer2
• Assignee: Amruth Sampath Assign to me
• Reporter: Amruth Sampath
• Created: 31/Aug/19 15:00
• Updated: 17/Nov/22 08:50
• Resolved: 15/Apr/20 00:52

Description

HIVE-14296 introduces this commit which adds synchronization to SessionManager.closeSession.

And it looks like it is used only for logging purposes.

In a busy hive server where 5-10 sessions are created closed every second, an increase in latency of any other downstream services (Zk, HDFS) causes a queueing effect (lot of threads getting blocked on SessionManager.closeSession) creating an induced latency of 3-5 minutes at times for just closing the session. 

Since the gauge (MetricsConstant.HS2_OPEN_SESSIONS) is already tracking the open session counts, the synchronization (along with the additional logging) can be removed without any functionality losses.

Issue Links

• fixes: HIVE-19624 the method closeSession of SessionManager has a synchronized, is it able to be removed?
• relates to: HIVE-19631 reduce epic locking in AbstractService