[HBASE-15453] [Performance] Considering reverting HBASE-10015 - reinstate synchronized in StoreScanner

• Type: Improvement
• Status: Resolved
• Priority: Critical
• Resolution: Won't Fix
• Component/s: Performance
• Assignee: Lars Hofhansl
• Reporter: Lars Hofhansl
• Created: 13/Mar/16 22:57
• Updated: 23/Dec/17 18:34
• Resolved: 23/Dec/17 18:34

Description

In HBASE-10015 back then I found that intrinsic locks (synchronized) in StoreScanner are slower that explicit locks.

I was surprised by this. To make sure I added a simple perf test and many folks ran it on their machines. All found that explicit locks were faster.

Now... I just ran that test again. On the latest JDK8 I find that now the intrinsic locks are significantly faster:
(OpenJDK Runtime Environment (build 1.8.0_72-b15))

Explicit locks:
10 runs mean:2223.6 sigma:72.29412147609237

Intrinsic locks:
10 runs mean:1865.3 sigma:32.63755505548784

I confirmed the same with timing some Phoenix scans. We can save a bunch of time by changing this back

Arrghhh... So maybe it's time to revert this now...?

(Note that in trunk due to ram_krish's work, we do not lock in StoreScanner anymore)

I'll attach the perf test and a patch that changes lock to synchronized, if some folks could run this on 0.98, that'd be great.