Chance Li commented on HBASE-19389:


thanks, sir.

{quote} less throughput, but way less CPU used (better 95th percentiles, etc), 
and handlers free for other tasks

Yes sir, this is our purpose.

{quote}Would it make sense to put this limit behind a configuration gate?

I think we need it. It is mainly for to enable us to 'remove' it , even though 
we can't totally remove it  because of the added counter on the path.

{quote}Also of note is how your compares show the asyncwal being slightly 
better than old wal.

Let me check again.  And this async_wal is one of Durablilty types. it's not 

[~carp84] ok, I will work on it.

> Limit concurrency of put with dense (hundreds) columns to prevent write 
> handler exhausted
> -----------------------------------------------------------------------------------------
>                 Key: HBASE-19389
>                 URL: https://issues.apache.org/jira/browse/HBASE-19389
>             Project: HBase
>          Issue Type: Improvement
>          Components: Performance
>    Affects Versions: 2.0.0
>         Environment: 2000+ Region Servers
> PCI-E ssd
>            Reporter: Chance Li
>            Assignee: Chance Li
>            Priority: Critical
>             Fix For: 2.0.0
>         Attachments: CSLM-concurrent-write.png, 
> HBASE-19389-branch-2-V2.patch, HBASE-19389-branch-2-V3.patch, 
> HBASE-19389-branch-2-V4.patch, HBASE-19389-branch-2-V5.patch, 
> HBASE-19389-branch-2-V6.patch, HBASE-19389-branch-2-V7.patch, 
> HBASE-19389-branch-2-V8.patch, HBASE-19389-branch-2.patch, metrics-1.png, 
> ycsb-result.png
> In a large cluster, with a large number of clients, we found the RS's 
> handlers are all busy sometimes. And after investigation we found the root 
> cause is about CSLM, such as compare function heavy load. We reviewed the 
> related WALs, and found that there were many columns (more than 1000 columns) 
> were writing at that time.

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