Worth saying that:
1) NUMA being a *hardware* topology thing, you can't turn NUMA on/off. If
you have NUMA hardware, NUMA is always on :-)
2) You can turn NUMA-*awareness* on/off at OS level
3) Additionally, you can turn NUMA-awareness on/of at Oracle level
Turning NUMA awareness on at OS level makes the OS aware and do some of its
memory/process placement in a NUMA aware mode, hopefully increasing
performance. Some processes/memory pages can dynamically be *migrated* to
the NUMA node where they should reside (for better locality).
That's great and exciting functionality for a performance geek, BUT this
increases complexity and unexpected operations (on the memory you want to
access), latency spikes etc.
The same goes for the *additional *NUMA awareness & placement functionality
at Oracle level. Even more complexity (and if you get unlucky, instability).
If you have a modern 2-socket server (where remote memory access latency is
not multiple *times* higher than local), keep NUMA awareness off at OS and
Oracle level). But, yeah with some (old?) 8 socket server, the multi-hop
remote access latency might be so slow that you need either NUMA placement
or try to constrain your entire workload (memory and processes) into a
single NUMA node, or 2-3 NUMA nodes that have the lowest latency between
each other. You might find out that most of your current CPU "usage" is
actually stalled CPU empty cycles, waiting for remote memory access...
Note that at least on Intel/AMD platform you can use Intel's Memory Latency
Checker (mlc) tool as I've done here in my hacking session:
- https://www.youtube.com/watch?v=5A531KE8O9Q&t=3640s
--
Tanel Poder
https://learn.tanelpoder.com
On Mon, Jun 20, 2022 at 5:10 AM Lothar Flatz <l.flatz@xxxxxxxxxx> wrote:
Thank you, Imar.
Am 20.06.2022 um 10:24 schrieb Ilmar Kerm:
On OEL8/RHEL8 NUMA can be turned on:
Requirements for Installing Oracle Database/Client 19c on OL8 or RHEL8
64-bit (x86-64) (Doc ID 2668780.1)
On OEL7 recommendation was to turn it off:
Requirements for Installing Oracle Database 19c on OL7 or RHEL7 64-bit
(x86-64) (Doc ID 2551169.1)
On Mon, Jun 20, 2022 at 10:11 AM Lothar Flatz <l.flatz@xxxxxxxxxx> wrote:
Hi,
I have a customer who runs a older Superdome Server with an 8 socket
board (7 sockets used).
End of quarter processing is approaching and we would need some
performance boost.
In theory we should have Numa effects. The hidden parameters for Numa (
"_enable_NUMA_support"
= TRUE according to MOS Doc ID 1956463.1) are not set.
I see a chance to get some quick improvement.
However, Numa is not my topic. I am a bit concerned by the fact that the
newest MOS entry I find dates back to db version 12.1.
Well, these kind of servers are not widely used any more.
Can somebody shed some light on the issue? Is NUMA still an issue in
version 19c?
Can we expect some improvement stetting NUMA support in the db?
Thanks
Lothar
--
Ilmar Kerm
