Re: ideal CPU/Memory relation

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_at_bluewin.ch> 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: http://www.soocs.de
>> Twitter: _at_OracleSK
>> 
>>> Lothar Flatz <l.flatz_at_bluewin.ch> 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
>>> --
>>> http://www.freelists.org/webpage/oracle-l

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