Instance Caging
Neil, November 22, 2011 - 8:38 pm UTC
Thanks Tom,
I had not come across Instance Caging before, but will read up on that with interest, plus it gives me extra ammunition for a case to upgrade from 10gR2 to 11gR2.
Do you know if Oracle support this as a method for licensing in the same way as hard partitioning such as LPAR's?
Again, thanks for the response
November 23, 2011 - 8:16 am UTC
It does not affect the license, no.
You need to hard partition for that.
It (instance caging) controls the user sessions only (dedicated/shared servers). It does not affect lgwr, dbwr, smon, etc. So, your instance can in fact use more than the prescribed number of CPU's - but it will keep the instance "under control".
In fact, even if you were running a single instance on a host, you might use instance caging to restrict the instance to say 80% of the cpu on that machine - leaving some aside for the clustering stuff and other OS processes - to avoid node eviction.
Limiting Memory Usage
stephan, November 23, 2011 - 9:22 am UTC
Hi Tom,
<quote>
With Exadata however you have the ability to control 1) memory allocated to each instance
In 10gr2 the only thing you truly have is 1) memory allocated to each instance.
</quote>
Can you say more about this? I'm aware of SGA_MAX_SIZE to limit the SGA, and PGA_AGGREGATE_TARGET - but that does not set a hard cap on the PGA. Is there any way to truly cap the memory usage for an instance? Or are you always subject to whatever the users might do, and the amount of PGA that might be allocated to support that?
Thanks!
November 23, 2011 - 9:38 am UTC
You can 100% control the size of the SGA.
The PGA however, you control to a degree. However, there is no way to totally limit it. For example, if you allowed 1,000 users to connect simultaneously (a really bad idea, regardless of machine size by the way) - we'd have to allocate 1,000 PGA's using dedicated server connections. If they all decided to open 5 queries that sorted - they'd add 5 workareas to that PGA allocation. If they then decided to run a bit of code:
for i in 1 .. 1000000 loop l_array(i) := rpad('*',32000,'*'); end loop;
that would get tacked on - and so on.
If you switch to shared server, then you could limit the amount of memory being used since the UGA would be in the large pool of the SGA now. That would probably cause that loop to blow up in individual sessions.
But you'd still have workareas in the shared server to consider - but since you control the number of shared servers - you would in fact be able to control the PGA memory very tightly.
So, under normal circumstances (dedicated server) - no, you cannot totally control the PGA.
Under shared server - yes, you can - because the UGA (user global area, session memory) is moved into the SGA's large pool and the PGA's for the shared servers would tend to be rather fixed in size.
RAC node Support
Rahim Khan, September 20, 2017 - 1:47 pm UTC
Hi
I would like to know that whats the maximum number of nodes supported by Oracle RAC?
September 21, 2017 - 2:53 am UTC
Depends on the database version, but from the 12.2 docs:
"MAXINSTANCES Clause
Specify the maximum number of instances that can simultaneously have this database mounted and open. This value takes precedence over the value of initialization parameter INSTANCES. The minimum value is 1. The maximum value is 1055. The default depends on your operating system."
about instances in RAC
Rajeshwaran Jeyabal, September 21, 2017 - 1:03 pm UTC
Connor,
Just to add that, It was from OTNYathra 2017 event at chennai.(
http://otnyathra.in/chennai/ )
It was "Sandesh Rao" (Senior director -RAC Developement) during the session 'Troubleshooting and Diagnosing Oracle Database 12.2 and Oracle RAC' at Room#1 he mentioned that the biggest implementation of RAC configuration for a banking customer has 48 nodes in it.