cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "B. Todd Burruss" <bburr...@real.com>
Subject Re: Persistently increasing read latency
Date Thu, 03 Dec 2009 23:40:38 GMT
in my situation it seems like the compaction process is being starved.
i'm hitting the server hard for the last 45 minutes and the compaction
pool is sitting at 1 active, 25 pending, and 7 completed.  it has been
at 1 active and 7 completed for about 20 minutes.  the pending have been
growing steadily since then.  and as i was typing it finally finished
another compaction, so they must be just taking forever.

snapshots of nodeprobe and iostats follow:

Pool Name                    Active   Pending      Completed
FILEUTILS-DELETE-POOL             0         0            116
MESSAGING-SERVICE-POOL            0         0              0
STREAM-STAGE                      0         0              0
RESPONSE-STAGE                    0         0              0
ROW-READ-STAGE                    1         4        8652560
LB-OPERATIONS                     0         0              0
COMMITLOG                         1         0       14695623
MESSAGE-DESERIALIZER-POOL         0         0              0
GMFD                              0         0              0
LB-TARGET                         0         0              0
CONSISTENCY-MANAGER               0         0              0
ROW-MUTATION-STAGE                1         1       14692604
MESSAGE-STREAMING-POOL            0         0              0
LOAD-BALANCER-STAGE               0         0              0
FLUSH-SORTER-POOL                 0         0             28
MEMTABLE-POST-FLUSHER             0         0             28
COMPACTION-POOL                   1        25              7
FLUSH-WRITER-POOL                 0         0             28
HINTED-HANDOFF-POOL               0         0              0


avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          61.85    0.00   26.68    7.73    0.00    3.74

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda             246.00     11456.00     18528.00      11456      18528
sda2          23074.00        20.50      1854.00         20       1854
sda1              0.00         0.00         0.00          0          0




On Thu, 2009-12-03 at 17:05 -0600, Jonathan Ellis wrote:
> 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?
> >



Mime
View raw message