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From "Freeman, Tim" <tim.free...@hp.com>
Subject RE: Persistently increasing read latency
Date Thu, 03 Dec 2009 22:58:41 GMT
>So this is working as designed, but the design is poor because it
>causes confusion.  If you can open a ticket for this that would be
>great.

Done, see:

   https://issues.apache.org/jira/browse/CASSANDRA-599

>What does iostat -x 10 (for instance) say about the disk activity?

rkB/s is consistently high, and wkB/s varies.  This is a typical entry with wkB/s at the high
end of its range:

>avg-cpu:  %user   %nice    %sys %iowait   %idle
>           1.52    0.00    1.70   27.49   69.28
>
>Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s    rkB/s    wkB/s avgrq-sz avgqu-sz
  await  svctm  %util
>sda          3.10 3249.25 124.08 29.67 26299.30 26288.11 13149.65 13144.06   342.04  
 17.75   92.25   5.98  91.92
>sda1         0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00     0.00     0.00
   0.00   0.00   0.00
>sda2         3.10 3249.25 124.08 29.67 26299.30 26288.11 13149.65 13144.06   342.04  
 17.75   92.25   5.98  91.92
>sda3         0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00     0.00     0.00
   0.00   0.00   0.00

and at the low end:

>avg-cpu:  %user   %nice    %sys %iowait   %idle
>           1.50    0.00    1.77   25.80   70.93
>
>Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s    rkB/s    wkB/s avgrq-sz avgqu-sz
  await  svctm  %util
>sda          3.40 817.10 128.60 17.70 27828.80 6600.00 13914.40  3300.00   235.33    
6.13   56.63   6.21  90.81
>sda1         0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00     0.00     0.00
   0.00   0.00   0.00
>sda2         3.40 817.10 128.60 17.70 27828.80 6600.00 13914.40  3300.00   235.33    
6.13   56.63   6.21  90.81
>sda3         0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00     0.00     0.00
   0.00   0.00   0.00

Tim Freeman
Email: tim.freeman@hp.com
Desk in Palo Alto: (650) 857-2581
Home: (408) 774-1298
Cell: (408) 348-7536 (No reception business hours Monday, Tuesday, and Thursday; call my desk
instead.)


-----Original Message-----
From: Jonathan Ellis [mailto:jbellis@gmail.com] 
Sent: Thursday, December 03, 2009 2:45 PM
To: cassandra-user@incubator.apache.org
Subject: Re: Persistently increasing read latency

On Thu, Dec 3, 2009 at 4:34 PM, Freeman, Tim <tim.freeman@hp.com> wrote:
>>Can you tell if the system is i/o or cpu bound during compaction?
>
> It's I/O bound.  It's using ~9% of 1 of 4 cores as I watch it, and all it's doing right
now is compactions.

What does iostat -x 10 (for instance) say about the disk activity?

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