RE: Fav. Urban Legend...Mem vs Disk

Not quite !! 99.999% or 'the five nines' sounds much better ;-)

With 64-bit computing we can address SGA sizes in the order of few TBs (if not PBs), why worry about disk I/Os except for two occasions ;-)) Then the 'five nines' can be 'nine nines'. Wow!! That sounds even better.. much much better ;-)))

• Kirti

-----Original Message-----
Sent: Wednesday, March 20, 2002 5:48 AM
To: Multiple recipients of list ORACLE-L

Cary Milsap from hotsos has much data to confirm an approximate 1:100 ratio between LIO time and PIO time.

Can we therefore conclude, that the buffer cache hit ratio should be 99%? :-)

Rgds, Bjørn.
On Wednesday 20 March 2002 10:48, Connor McDonald wrote:
> Some rudimentary testing on a laptop here (500Mhz,
> 512M RAM, typical single disk)
>
> a) visiting a single block via 4,000,000 logical IO's
> got me approx 35000 gets/sec
>
> b) repeated full table scans similar system got me
> approx 350 phys reads/sec
>
> After this extensive, thorough and exhaustive
> exercise, I can definitely say that memory access
> versus disk access (as it pertains to Oracle) is 100
> times faster on this machine in single user mode
>
> I think we can generalise this to be the rule for all
> servers under all conditions :-)
>
> Connor
>
>

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Author: Deshpande, Kirti
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