Re: What MB/s is pulled from your buffer cache?
- From: Tanel Poder <tanel@xxxxxxxxxxxxxx>
- To: rjoralist2@xxxxxxxxxxxxxxxxxxxxx
- Date: Thu, 14 Feb 2013 01:49:49 +0200
By the way the "logical read bytes from cache" metric doesn't mean that
this amount of bytes were actually processed / transferred from buffer
cache memory to CPUs. An example would be a nested loop join or a filter
loop, which probes some index/table millions of times in a loop - taking
only one (or a couple of) rows each time.
So, on each iteration you could only be touching only a couple of hundred
bytes worth of memory lines in that 8kB buffer each time (btw I'm not
talking about all the other memory access that's going on when running
oracle code).
This is different from the "physical read total bytes" metric in the sense
that when you read 8kB from disk, you have to read it all in (and checksum
it from end to end) even if you plan to read only one row from it.
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*Tanel Poder*
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On Wed, Feb 13, 2013 at 5:12 PM, Rich Jesse <
rjoralist2@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Martin writes:
>
> > So it's 4,970,209,998 Bytes per second overall. Fairly less than yours.
> :)
>
> At 4GB/s, that's roughly 40 times my number. :)
>
> My server uses DDR2 PC2-5300 RAM (man, would I love to upgrade), which
> gives
> it a theoretical max bandwidth of 10.6GB/s, assuming a dual-channel
> configuration. I'm not sure how an IBM p-series is architected CPU-to-RAM,
> but I just saw a peak transfer of over 13GB/s.
>
> Fun stuff. Thanks!
>
> Rich
>
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>
>
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