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Mladen Gogala wrote:
> On Thu, 09 Feb 2006 15:14:20 +0100, Fabrizio Magni wrote:
>
>> The second dd has its I/O merged. >> >> Consider this controversial but the I/O scheduler eliminate the need to >> have oracle block size "aligned" to file system block size (even without >> direct I/O). >>
Test was performed on a SLES9 with cfq scheduler. The result would be the same even with the other three (or with the older elevator).
A dd doesn't represent the typical database workload but it shows what
an I/O scheduler can do.
This component relax the rule of thumb "db block size=file system
blocksize" suggested by many.
For example: with a db block size of 8k and a filesystem of 4k every
oracle request isn't translated in two I/O of 4k each but in a single 8k
operation.
The I/O merging is only one of the function of the scheduler.
If you play with ETL and datawarehouses you can have significant performance enhancement.
For an OLTP the deadline scheduler could be a good solution.
-- Fabrizio Magni fabrizio.magni_at_mycontinent.com replace mycontinent with europeReceived on Fri Feb 10 2006 - 11:51:50 CST