IO bound Sybase backups

Mark Tinberg mtinberg at securepipe.com
Thu Oct 14 19:42:01 CDT 2004


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On Thu, 14 Oct 2004, McDougall, Marshall (FSH) wrote:

> When we do a backup of the database, the machine get severely io bound (top
> output below), and the machine becomes barely useable:

vmstat 1 output for a period of time would be helpful.

> 09:42:42  up 49 days, 22:55,  3 users,  load average: 8.89, 8.37, 5.58
> 72 processes: 71 sleeping, 1 running, 0 zombie, 0 stopped
> CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle
>            total    0.0%    0.0%    4.7%   0.0%     0.4%   94.6%    0.2%
>            cpu00    0.0%    0.0%    2.4%   0.0%     0.0%   97.4%    0.2%
>            cpu01    0.0%    0.0%    6.8%   0.0%     0.0%   93.2%    0.0%
>            cpu02    0.0%    0.0%    2.6%   0.0%     1.6%   95.4%    0.4%
>            cpu03    0.0%    0.0%    7.0%   0.0%     0.2%   92.6%    0.2%
> Mem:  3869568k av, 3851296k used,   18272k free,       0k shrd,    5256k buff
>                    2986960k actv,  570492k in_d,   58980k in_c
> Swap: 2048248k av, 2048248k used,       0k free                 3701660k cached


This shows that your machine has fully filled up 2G of swap, and is also
using most of its memory for disk cache?  I imagine that your machine is
probably swapping like crazy, which is why you have such a pronounced IO
bottleneck.  It seems like maybe Sybase internal buffers are competing for
memory with the filesystem buffers, at least I've seen that kind of 
problem with InnoDB based databases.

Figure out why your server is using swap and you'll probably figure out 
your bottleneck.

- -- 
Mark Tinberg <MTinberg at securepipe.com>
Staff Engineer, SecurePipe Inc.
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