Re: Designing database tables for performance?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 23 Feb 2007 21:44:35 GMT
Message-ID: <7fJDh.384$PV3.6587_at_ursa-nb00s0.nbnet.nb.ca>
>
>
> Not an absurdity, you just aren't paying attention to how the I/O is
> counted. From Oracle's point of view, if the desired data exists in
> Oracle's buffers, that is a logical I/O.
Date: Fri, 23 Feb 2007 21:44:35 GMT
Message-ID: <7fJDh.384$PV3.6587_at_ursa-nb00s0.nbnet.nb.ca>
> On Feb 23, 5:24 am, "Cimode" <cim..._at_hotmail.com> wrote:
>
>>On Feb 23, 2:06 pm, Frank Hamersley <terabitemigh..._at_bigpond.com> >>wrote: >> >>>Cimode wrote: >> >>>[..] >> >>>>Yep. Last time I discussed database issues with an ORACLE guru, he >>>>was trying to convince me that RAM was logical as opposed to Hard >>>>drive which was physical. To the ORACLE gurus, as soon as it is in >>>>memory, it becomes totally logical. A total absurdity of course... >> >>>He was prolly talking about the types of IO's for a query that the >>>optimiser predicts and execution engine encounters. Sybase uses the >>>same terminology and weights them differently when costing out >>>(possible) plans. >> >>>Cheers Frank. >> >>In what RAM would be less physical than HD ? For any reason, an >>absurdity is an absurdity.
>
>
> Not an absurdity, you just aren't paying attention to how the I/O is
> counted. From Oracle's point of view, if the desired data exists in
> Oracle's buffers, that is a logical I/O.
To exactly what sort of logic does it apply? Predicate logic? First order? Second order?
If Oracle has to ask the OS
> to give it stuff to put in the buffers (or Oracle knows that it has to
> get it off a disk using its own raw I/O), that is counted as a
> physical I/O.
Why not count one as a cache hit and one as a miss? How does it help to
create a new and obscure term by borrowing a completely unrelated word
with an existing well-defined meaning?
[snip]