Re: Detecting xxx fragmentation/corruption?
Date: Fri, 09 May 2008 19:55:05 -0600
To supplement Jared's response... Inline
Peter Teoh wrote:
> Unlike memory, where access time almost zero, accessing the disk is
> much slower. So sometimes I thought it will be better to spread out
> the data - thus enable simultaneous read by the different heads in the
> disk, just like those RAID design. Ie, fragmentation via
> distribution the blocks out in the disk can improve performance - can
> such things happened?
In terms of reading data in memory, access time may be almost zero, but the time required to read a block in memory is not thousands of times faster than reading it from disk. I don't recall the exact figure from a Cary Millsap presentation ("Why You Should Focus on LIOs"?)some years ago, but the difference was something like 42 times. If you add in time required to create a read consistent version, a single logical i/o could take much more time than a physical i/o.
-- Daniel Fink Oracle Performance, Diagnosis, Data Recovery and Training OptimalDBA http://www.optimaldba.com Oracle Blog http://optimaldba.blogspot.com Lost Data? http://www.ora600.nl/introduction.htm -- http://www.freelists.org/webpage/oracle-lReceived on Fri May 09 2008 - 20:55:05 CDT