I love a good "religious" debate! Most traffic on one topic here in a while.
The "correct" answer is obviously 42!
Clay Jackson
BTW, Frits - your mention of NUMA actually gave me some clues on chasing a
performance problem I'm seeing with graphics on a Raspberry Pi 4; so there's no
such thing as a "fruitless" discussion.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> On Behalf
Of Frits Hoogland
Sent: Friday, August 19, 2022 5:55 AM
To: Lothar Flatz <l.flatz@xxxxxxxxxx>
Cc: Stefan Koehler <contact@xxxxxxxx>; oracle-l@xxxxxxxxxxxxx
Subject: Re: ideal CPU/Memory relation
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What really matters here is the physical layout, because modern CPUs have
memory attached to them more or less directly.
This principle of CPUs with their memory attached is called NUMA.
By default, at least in the past, Oracle and linux did not have numa specific
optimisations enabled.
With these not being enabled, memory is divided evenly over "all memories", and
thus your memory latency is the average of all memory latencies.
With non-ideal NUMA (having different and higher latencies between certain numa
nodes), the latency might be higher than a smaller box with less numa nodes,
and thus will memory closer by, and thus with lower latency.
If numa is enabled, it still needs care and attention. Then memory might be
explicitly allocated locally, but if you make the scheduler schedule a process
on a non-numa-local CPU, your memory all of a sudden is remote and slow.
Frits
On 19 Aug 2022, at 12:28, Lothar Flatz <l.flatz@xxxxxxxxxx> wrote:
Hi all,
thanks fro responding. We are actually talking of a big server. Provider
offered 288 cores (16 Cpus a 18 cores, these are 8354H, one CPU can address
1,2 TB) and 6 TB RAM.
We said we only need 144 cores. Reaction was: then we need more RAM due the
ideal CPU/RAM relation.
So far I can see it ought to be the other way around, if at all..
Regards
Lothar
Am 19.08.2022 um 12:17 schrieb Stefan Koehler:
Hello Lothar,
there are such databases like SAP HANA that use such an approach - quoting
doc: "Using core-to-memory ratios which can be derived from the certified
HANA listings. The memory requirement drives the number of cores required."
... but I guess you are using Oracle and never have seen such
guidelines in the field until yet :-)
Best Regards
Stefan Koehler
Independent Oracle performance consultant and researcher
Website:
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Lothar Flatz <l.flatz@xxxxxxxxxx> hat am 19.08.2022 09:02 CEST geschrieben:
Hi,
had somebody ever heard of a ideal CPU/Memory relation for a
database server?
A supplier of a customer stated such thing, I suppose they made it
up.
Any comments?
Thanks
Lothar
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