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  1. #1

    How to show a poor performing VPS through logs?

    Hi everyone,

    I'm having an issue with my CentOS 5.5 VPS being sluggish, and I've opened a ticket for it with my provider. However, they want logs that prove the system is slow.

    Right now, the server should be very lightly loaded - it only has a private webserver and a public mailserver for my domain, with only about 80 emails per day (no attachments). However, operations like saving a file through "vi" (2400 bytes) can take 10 seconds, doing an "ls" on a directory with only 2 files can take 5 seconds, and exiting from my root shell back to the user shell can take 5 seconds as well.

    What kind of logs can I use to prove I'm getting this poor performance?

  2. #2
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    You can test I/O with the following command:
    dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync

    If you get less than 10mb there is something wrong, probably overloaded Node or very slow drive(s).
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  3. #3
    I'm getting reasonable disk performance based on that test - 14 to 32 MB/s over several tests.

    However, doing an "ls" took 14 seconds on a directory with only 1 files!

    [[email protected] tmp]# date;ls;date
    Tue Apr 26 13:11:40 PDT 2011
    test
    Tue Apr 26 13:11:54 PDT 2011

  4. #4
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    I suggest you take in an admin for a short moment to drill down to the problem, especially if it's a non-obvious one.

    To go with your specific question the kind of log I'd try is running "sar" in the collector mode. Google for it and be sure it includes the disk stats.
    That way you can grab data for a whole day or longer.

    it sounds like every *write* is delayed, so it would be very interesting to watch the disk response times.
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  5. #5
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    Quote Originally Posted by Skidmark View Post
    Hi everyone,

    I'm having an issue with my CentOS 5.5 VPS being sluggish, and I've opened a ticket for it with my provider. However, they want logs that prove the system is slow.

    Right now, the server should be very lightly loaded - it only has a private webserver and a public mailserver for my domain, with only about 80 emails per day (no attachments). However, operations like saving a file through "vi" (2400 bytes) can take 10 seconds, doing an "ls" on a directory with only 2 files can take 5 seconds, and exiting from my root shell back to the user shell can take 5 seconds as well.

    What kind of logs can I use to prove I'm getting this poor performance?


    edit: also try to grab the number of swap in/out and context switches
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  6. #6
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    Use 'time' to capture the runtime of commands, e.g., with the ls command:

    Code:
    [[email protected]:~] cd /etc
    [[email protected]:/etc] time ls
    ...
    
    real    0m0.002s
    user    0m0.001s
    sys     0m0.000s

  7. #7
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    Quote Originally Posted by sleddog View Post
    Use 'time' to capture the runtime of commands, e.g., with the ls command:

    Code:
    [[email protected]:~] cd /etc
    [[email protected]:/etc] time ls
    ...
    
    real    0m0.002s
    user    0m0.001s
    sys     0m0.000s
    time only starts counting when the process started to run, but not any delay with forking it. So it can sit for 30seconds and then say the process took 5s. Very annoying, I never tried time time ls though
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  8. #8
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    Skidmark, one thing to learn is every minute/hour you put into trying to prove your current setup / config sucks.. you're just helping whomever you're paying make more $. Just step back, backup your data and find a new home.

    You'll thank me later for just finding a place that doesn't give you any reason to have to "prove" squat in logs. If its slow, they should look into it, regardless of logs. You said its slow.. they have a standard and if your standard and their standard don't meet.. I think its time to tell them to kick rocks
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  9. #9
    Quote Originally Posted by wartungsfenster View Post
    time only starts counting when the process started to run, but not any delay with forking it.
    Interesting. Is that true both for the shell's built-in 'time' and for the external 'time' command (e.g., /usr/bin/time)?
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  10. #10
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    Quote Originally Posted by raindog308 View Post
    Interesting. Is that true both for the shell's built-in 'time' and for the external 'time' command (e.g., /usr/bin/time)?
    Good question. I should've looked into that more curiously but -
    I only had that issue on a debian lenny box when the software raid did it's periodic scan / resync.
    And that ran at Sunday night, so I did not really track it down, just worked around and opened a bug. They since fixed it to use ionice, so it won't happen like this any more.

    In an ideal world the buildin should work instantly, but maybe it would still be waiting for an update of the $HISTFILE? If you can wait a week or two I will test it and post back here since I'm interested now
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  11. #11
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    I suggest you change your hosts.

    These problems sound like overcrowding on the node or abusive neighbors, neither of which will be easy to deal with.

  12. #12
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    Quote Originally Posted by Skidmark View Post
    I'm getting reasonable disk performance based on that test - 14 to 32 MB/s over several tests.

    However, doing an "ls" took 14 seconds on a directory with only 1 files!
    Sounds like an internal resource shortage, but it's unclear where the bottleneck is.

    I suggest that you install webmin. Once installed, click the System link and open Running processes. You can monitor memory & cpu resource usage in there, broken down by process. You should be able to learn something there.

    You might also look around /var/log/ for any rogue log files growing out of control. Sometimes a process will consume all of your resources doing verbose logging for no good reason (written by a programmer who deserves to be horsewhipped publicly).

  13. #13
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    If the slowdowns that you described are truly happening on the host side, then there's no need for you to "prove" the poor performance. That's as evident as it gets and asking for proof is just stalling the inevitable cancellation.

  14. #14
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    Quote Originally Posted by Orien View Post
    If the slowdowns that you described are truly happening on the host side, then there's no need for you to "prove" the poor performance. That's as evident as it gets and asking for proof is just stalling the inevitable cancellation.
    Oh sure. If it's on the host side then they are more aware of it than he is. But we haven't established where the problem is yet.

  15. #15
    I got the following sar results (not really clear on how to run it properly yet), but the %iowait seems a bit high at certain times - is this any kind of indication of a disk problem?

    12:10:24 AM CPU %user %nice %system %iowait %steal %idle
    12:30:12 AM all 0.01 0.00 0.01 12.61 0.00 87.37
    12:50:27 AM all 0.01 0.00 0.01 11.22 0.00 88.76
    01:00:19 AM all 0.00 0.00 0.01 3.07 0.00 96.91
    01:10:25 AM all 0.00 0.00 0.01 5.05 0.00 94.93
    01:30:48 AM all 0.00 0.00 0.01 12.61 0.00 87.38
    01:40:34 AM all 0.01 0.00 0.01 5.61 0.00 94.37
    01:50:17 AM all 0.00 0.00 0.01 2.73 0.00 97.26
    02:00:12 AM all 0.01 0.00 0.01 3.02 0.00 96.96
    02:11:09 AM all 0.00 0.00 0.01 9.61 0.00 90.38
    02:20:41 AM all 0.00 0.00 0.01 7.38 0.00 92.61
    02:30:14 AM all 0.01 0.00 0.01 4.53 0.00 95.45
    02:41:07 AM all 0.00 0.00 0.01 10.16 0.00 89.83
    02:50:38 AM all 0.01 0.00 0.01 6.21 0.00 93.77
    03:00:04 AM all 0.01 0.00 0.01 1.00 0.00 98.98
    03:10:13 AM all 0.00 0.00 0.01 2.51 0.00 97.48
    03:20:28 AM all 0.01 0.00 0.01 4.82 0.00 95.16
    03:30:06 AM all 0.26 0.00 0.20 0.87 0.00 98.67
    03:40:13 AM all 0.59 0.00 0.45 2.42 0.00 96.54
    03:50:01 AM all 0.01 0.00 0.01 0.21 0.00 99.78
    04:00:01 AM all 0.01 0.00 0.01 0.08 0.00 99.91
    04:10:05 AM all 0.00 0.00 0.01 0.72 0.00 99.27
    04:20:32 AM all 0.01 0.00 0.01 4.69 0.00 95.29
    04:30:09 AM all 0.00 0.00 0.01 1.47 0.00 98.52
    04:40:31 AM all 0.01 0.00 0.01 4.38 0.00 95.60
    04:50:07 AM all 0.00 0.00 0.01 2.31 0.00 97.68
    05:00:01 AM all 0.00 0.00 0.01 0.03 0.00 99.95
    05:10:01 AM all 0.00 0.00 0.01 0.00 0.00 99.99
    05:20:01 AM all 0.00 0.00 0.01 0.16 0.00 99.82
    05:30:01 AM all 0.00 0.00 0.01 0.37 0.00 99.62
    05:40:06 AM all 0.01 0.00 0.02 0.86 0.00 99.11
    05:50:01 AM all 0.00 0.00 0.01 0.00 0.00 99.99
    06:00:01 AM all 0.01 0.00 0.01 0.17 0.00 99.82
    06:10:02 AM all 0.00 0.00 0.01 0.38 0.00 99.61
    06:20:51 AM all 0.00 0.00 0.01 7.04 0.00 92.95
    06:30:55 AM all 0.00 0.00 0.01 10.59 0.00 89.40
    06:50:37 AM all 0.01 0.00 0.01 12.39 0.00 87.59
    07:00:03 AM all 0.00 0.00 0.01 0.59 0.00 99.40
    07:10:13 AM all 0.01 0.00 0.01 2.57 0.00 97.41
    07:20:04 AM all 0.00 0.00 0.01 0.58 0.00 99.41
    07:30:02 AM all 0.01 0.00 0.01 0.30 0.00 99.68
    07:40:05 AM all 0.01 0.00 0.01 0.59 0.00 99.39
    07:50:01 AM all 0.00 0.00 0.01 0.00 0.00 99.99
    08:00:02 AM all 0.01 0.00 0.01 0.16 0.00 99.83
    08:10:01 AM all 0.00 0.00 0.01 0.00 0.00 99.99
    08:20:01 AM all 0.01 0.00 0.02 0.00 0.00 99.97
    08:30:01 AM all 0.00 0.00 0.01 0.00 0.00 99.99
    08:40:01 AM all 0.00 0.00 0.01 0.28 0.00 99.71
    08:50:01 AM all 0.01 0.00 0.01 0.00 0.00 99.99
    09:00:02 AM all 0.01 0.00 0.03 0.44 0.00 99.52
    09:10:01 AM all 0.00 0.00 0.01 0.01 0.00 99.98
    09:20:04 AM all 0.00 0.00 0.01 0.46 0.00 99.53
    09:30:21 AM all 0.00 0.00 0.01 3.67 0.00 96.32
    09:40:02 AM all 0.01 0.00 0.02 2.16 0.00 97.81
    Average: all 0.02 0.00 0.02 3.75 0.00 96.20

  16. #16
    Quote Originally Posted by wartungsfenster View Post
    I suggest you take in an admin for a short moment to drill down to the problem, especially if it's a non-obvious one.

    To go with your specific question the kind of log I'd try is running "sar" in the collector mode. Google for it and be sure it includes the disk stats.
    That way you can grab data for a whole day or longer.

    it sounds like every *write* is delayed, so it would be very interesting to watch the disk response times.
    I downloaded the sysstat package and modified the cron.d sa1 command to include the "-d" switch, but when I run "sar -d", I don't see any statistics.

  17. #17
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    Quote Originally Posted by Skidmark View Post
    I'm getting reasonable disk performance based on that test - 14 to 32 MB/s over several tests.

    However, doing an "ls" took 14 seconds on a directory with only 1 files!

    [[email protected] tmp]# date;ls;date
    Tue Apr 26 13:11:40 PDT 2011
    test
    Tue Apr 26 13:11:54 PDT 2011
    14-32MB/s is actually pretty low. I would consider anything under 80-90MB/s to be very low. Also, looking at your iowait times, I'm seeing it spike between 4-15% or so -- again, that's simply too high in my opinion.
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  18. #18
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    Last time I had a report like that, someone was running a minecraft server on that same node. The other time was a raid rebuild. You ideally shouldn't have a iowait like that on an otherwise idle VPS.

    That said, I wouldn't call it an 'the house is burning down' type of log. The one with the minecraft server just noted it, responded that unless it got to 30%, it's acceptable and moved on. Granted, they later moved all the 'abusers' off that node, but that's another story

    If you can stomach it, I might suggest installing munin-node on it as well to gather more data. It helps make more sense of it when you can correlate things like fork-rate and context switches to the cpu graph.

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