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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Persistently increasing read latency
Date Thu, 03 Dec 2009 23:05:52 GMT
Thanks for looking into this.  Doesn't seem like there's much
low-hanging fruit to make compaction faster but I'll keep that in the
back of my mind.

-Jonathan

On Thu, Dec 3, 2009 at 4:58 PM, Freeman, Tim <tim.freeman@hp.com> wrote:
>>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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