Re: troubleshooting slow I/O performance.

On 05/08/2018 04:13 AM, Stefan Koehler wrote:
> Hello Chris,
> at first you need to identify where the time is spent in the whole I/O stack (e.g. I/O scheduler, SCSI, etc.).
>
> For example you can do that with blktrace on Linux: http://www.fis.unipr.it/doc/blktrace-1.0.1/blktrace.pdf
>
> Anything further is related to this drill-down outcome :-)
>
> Best Regards
> Stefan Koehler
>
> Independent Oracle performance consultant and researcher
> Website: http://www.soocs.de
> Twitter: _at_OracleSK
>
>

There is rarely need to lose time by doing blktrace. If disks are too slow, the ONLY real answer are faster disks. I used to play with IO elevators, read ahead, systemtap and stuff like that, but the truth is that whenever I delved into that stuff, nothing useful ever came out of it. When IO is too slow, the faster disks are the only solution.  No amount of tuning will turn a Ford Taurus into a Ferrari. Storage configuration is usually planned ahead of configuring the database. It may even be prudent, I apologize for using harsh language, to do some testing ahead of building the whole cluster. This sounds like the configuration done by the most interesting DBA in the world: the one who doesn't test his stuff often, but when he does so, he does it in production.

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Mladen Gogala
Database Consultant
Tel: (347) 321-1217

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