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Date: Fri, 5 Feb 2016 08:12:39 +0000 (UTC)
From: "Heng Chen (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12936660.1454577860000.309245.1454659959994@Atlassian.JIRA>
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Subject: [jira] [Commented] (HBASE-15213) Fix increment performance
 regression caused by HBASE-8763 on branch-1.0
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    [ https://issues.apache.org/jira/browse/HBASE-15213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15133812#comment-15133812 ] 

Heng Chen commented on HBASE-15213:
-----------------------------------

As for patch, how about move w.markCompleted() out of sync scope,  we could mark entry without lock, it will be better.

{code}
       do {
         synchronized (writeQueue) {
-          // writeQueue won't be empty at this point, the following is just a safety check
+          w.markCompleted();
+
{code}


> Fix increment performance regression caused by HBASE-8763 on branch-1.0
> -----------------------------------------------------------------------
>
>                 Key: HBASE-15213
>                 URL: https://issues.apache.org/jira/browse/HBASE-15213
>             Project: HBase
>          Issue Type: Bug
>          Components: Performance
>            Reporter: Junegunn Choi
>            Assignee: Junegunn Choi
>         Attachments: HBASE-15213.branch-1.0.patch
>
>
> 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.


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