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From Adam Kocoloski <kocol...@apache.org>
Subject Re: High latency (40ms) and low request rate (10 rps) under windows
Date Wed, 26 Oct 2011 23:56:13 GMT
CouchDB is smart enough to collect writes from multiple concurrent clients into a "group commit"
and issue only one fsync to durably store all of them in one go.  It's a bit like generating
a _bulk_docs request under the hood.  That's the main reason you see the jump from 10/sec
to 300/sec.

Adam

On Oct 26, 2011, at 7:52 PM, Riyad Kalla wrote:

> Hmm, I see what you mean. If a single connection isnt pegging any of the hardware and
multiple connections are a magnitude times faster, I am not sure what would be keeping the
single connection from performning faster.
> 
> Maybe someone else can hop in with ideas? 
> 
> R
> 
> On Oct 26, 2011, at 4:32 PM, Konstantin Cherkasoff <k.cherkasoff@gmail.com> wrote:
> 
>> Hi!
>> 
>>> What happens when you set delayed_commits to true?
>> With delayed_commits I got about 150 rps so delayed_commits mode is 15
>> times faster.
>> 
>>> With that off you are requiring an fsync (iirc)  after every value written and
then are at the
>>> mercy at your disks write performance (but not in the sense of burst-write
>>> as these are individual, disparate write requests coming in).
>> 
>> Yes, I understand that many small writes and fsyncs can be a
>> bottleneck in this case.
>> But I found that the increase of number of concurrent requests lead to
>> an increase in the request rate.
>> For example (100 concurent requests)
>>> ab -k -t 10 -c 100 -n 1000000 -p ab.json -T "application/json" http://localhost:5984/bench
>> shows about 300 RPS (writes and fsyncs) on the same hardware.
>> 
>> So, I suppose that 10 requests per second actually is not the limit
>> for this hard disk.
>> And there may be some other problem.
>> 
>>> Also, is this build Couch Single Server from Couchbase or some other Windows
build of Couch?
>> I tried Couchbase 1.2.0 and
>> this build https://github.com/downloads/dch/couchdb/setup-couchdb-1.1.0+COUCHDB-1152_otp_R14B03.exe
>> 
>> 
>> --
>> Konstantin


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