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Message-ID: <48583BA6.1050507@gmail.com>
Date: Tue, 17 Jun 2008 15:33:10 -0700
From: Brad Schick <schickb@gmail.com>
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To: couchdb-user@incubator.apache.org
Subject: Re: Bad write performance
References: <48580C64.40806@gmail.com>
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On 06/17/2008 12:11 PM, Brad Schick wrote:
> I am seeing very poor write performance running CouchDB on Ubuntu Linux
> 8.04. I built CouchDB from source about a week ago, and I am using the
> Python wrapper to access it all on localhost.
>
> I am trying to add over 90,000 documents (each is about 400 bytes) and
> finding that I can only add about 16 documents per second. And while
> this is happening, my CPU is about 75% idle. 
>   
I'm running these tests on an old machine running a Gnome desktop, so it
is not a clean environment, but it seems like the bottleneck should
still be apparent. So far disk access looks like the most likely issue.
Running a single writer client, I get the following results from 'iostat
-x sdb -k 1'

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          21.00    0.00    7.00    1.00    0.00   71.00

Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s
avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00   78.00     0.00   326.50    
8.37     0.77   10.00   9.54  74.40

Although it doesn't look totally saturated, I found a fairly similar
maximum %util running 'stress -d 1 --hdd-bytes 400'  (many small disk
writes).

Here is the output of 'vmstat 1' with one writer client running

procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy
id wa
 1  0  39224 589712     40 156556    0    0     0   321  502  873 23  9
67  1
 0  0  39224 589656     40 156624    0    0     0   321  388  630 24  6
69  1
 0  0  39224 589492     40 156680    0    0     0   279  460  804 23  6
70  1
 0  0  39224 589476     40 156740    0    0     0   277  370  575 20  8
71  1

The only real differences between that and "idle" (shown below) are the
blocks-out a small amount of iowait.

procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy
id wa
 0  0  39224 581296     40 167920    0    0     0    10  305  570  3  3
94  0
 0  0  39224 581296     40 167920    0    0     0     0  194  306  3  1
96  0
 0  0  39224 581296     40 167920    0    0     0     0  283  528  3  2
95  0
 0  0  39224 581296     40 167920    0    0     0     0  193  297  3  0
97  0

I'm not sure what else to check from the OS. I found erlang's fprof
(http://www.erlang.org/doc/man/fprof.html), but I haven't tried to
figure how to start couchdb in that environment. I'll test block updates
next.

-Brad