Re: Detecting xxx fragmentation/corruption?

  • From: Daniel Fink <daniel.fink@xxxxxxxxxxxxxx>
  • To: Oracle-L Freelists <oracle-l@xxxxxxxxxxxxx>
  • 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.

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