[HBASE-15213] Fix increment performance regression caused by HBASE-8763 on branch-1.0

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.1.4, 1.0.4
• Component/s: Performance
• Hadoop Flags: Reviewed

Release Note

Fixes performance regression in increment/append and checkAnd* operations in hbase-1.0.x and hbase-1.1.x. This fix is not needed in hbase-1.2 and on up. They have HBASE-12751 which does effectively the same thing.

• Assignee: Junegunn Choi
• Reporter: Junegunn Choi
• Created: 04/Feb/16 09:24
• Updated: 20/Jul/16 08:17
• Resolved: 06/Feb/16 02:04

Description

This is an attempt to fix the increment performance regression caused by HBASE-8763 on branch-1.0.

I'm aware that hbase.increment.fast.but.narrow.consistency was added to branch-1.0 (HBASE-15031) to address the issue and a separate work is ongoing on master branch, but anyway, this is my take on the problem.

I read through HBASE-14460 and HBASE-8763 but it wasn't clear to me what caused the slowdown but I could indeed reproduce the performance regression.

Test setup:

• Server: 4-core Xeon 2.4GHz Linux server running mini cluster (100 handlers, JDK 1.7)
• Client: Another box of the same spec
• Increments on random 10k records on a single-region table, recreated every time

Increment throughput (TPS):

Num threads	Before HBASE-8763 (d6cc2fb)	branch-1.0	branch-1.0 (narrow-consistency)
1	2661	2486	2359
2	5048	5064	4867
4	7503	8071	8690
8	10471	10886	13980
16	15515	9418	18601
32	17699	5421	20540
64	20601	4038	25591
96	19177	3891	26017

We can clearly observe that the throughtput degrades as we increase the number of concurrent requests, which led me to believe that there's severe context switching overhead and I could indirectly confirm that suspicion with cs entry in vmstat output. branch-1.0 shows a much higher number of context switches even with much lower throughput.

Here are the observations:

• WriteEntry in the writeQueue can only be removed by the very handler that put it, only when it is at the front of the queue and marked complete.
• Since a WriteEntry is marked complete after the wait-loop, only one entry can be removed at a time.
• This stringent condition causes O(N^2) context switches where n is the number of concurrent handlers processing requests.

So what I tried here is to mark WriteEntry complete before we go into wait-loop. With the change, multiple WriteEntries can be shifted at a time without context switches. I changed writeQueue to LinkedHashSet since fast containment check is needed as WriteEntry can be removed by any handler.

The numbers look good, it's virtually identical to pre-HBASE-8763 era.

Num threads	branch-1.0 with fix
1	2459
2	4976
4	8033
8	12292
16	15234
32	16601
64	19994
96	20052

So what do you think about it? Please let me know if I'm missing anything.

Issue Links

• is related to: HBASE-14460 [Perf Regression] Merge of MVCC and SequenceId (HBASE-8763) slowed Increments, CheckAndPuts, batch operations