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https://issues.apache.org/jira/browse/HBASE-15213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15133634#comment-15133634
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Heng Chen commented on HBASE-15213:
-----------------------------------
Thanks for your explain! [~junegunn]
You are right, we could mark entry as complete after sync successfully
immediately, there is no need to wait other entries complete and current one
come to be first in writeQueue, so as your mentioned, other handlers could
remove it while current thread in waiting state.
{quote}
This stringent condition causes O(N^2) context switches where n is the number
of concurrent handlers processing requests.
{quote}
This is why you make writeQueue from list to set, right? Sorry, i have a
little confused about this sentence.
> 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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