RE: RAC install on Linux

From: Stefan Koehler <>
Date: Fri, 23 Feb 2018 11:20:36 +0100 (CET)
Message-ID: <>

Hey guys,


Never ever over-subscribe memory in a VM environment for database server VMs (e.g. memory ballooning). In theory you can over-subscribe memory in the VM itself (e.g. with multiple databases running in it) but this works only in case of "lazy memory allocation" for some specific time - in case of huge pages this does not work as the huge pages pool is a "separate" allocated memory area, cut-off right away and needs to be defined via kernel parameter. Heap memory (e.g. PGA) is a whole different topic.

_at_Ruel: "Huges pages remain pinned in memory and are not replaced, so the kernel swap daemon has no work to do in managing them" - so yes huge pages are locked and can not be swapped. "PRE_PAGE_SGA" is a different topic - Frits Hoogland has written a great blog post about it and what it really means (documentation is not true):

Huge pages can be used with manual memory management or ASMM but not with AMM (different implementation).

Best Regards
Stefan Koehler

Independent Oracle performance consultant and researcher Website:
Twitter: _at_OracleSK

> "Ruel, Chris" hat am 22. Februar 2018 um 21:37 geschrieben:
> Someone correct me if I am wrong but HP's do not lock memory. They just use a larger page size. In fact some people had problems locking memory with HP's enabled. I don't know if Oracle ever admitted to this being a bug. This note is a little older but I know it affected us as late as
> Oracle Support Document 1276966.1 (Rac Nodes Frequently Evicted (Rebooted) By CRS When PRE_PAGE_SGA is Set to True) can be found at:
> Also, looking at the thread below, this is news to me that you must use ASMM with HP's. We use HP's with standard memory management in some cases and it seems to work fine. I know that AMM is a no-no.
> Chris..
> _____________________________________________________________________
> Chris Ruel * Oracle Database Administrator * Lincoln Financial Group
> * Desk:317.759.2172 * Cell 317.523.8482
> -----Original Message-----
> From: [] On Behalf Of Hameed, Amir
> Sent: Thursday, February 22, 2018 3:06 PM
> To:;
> Cc: Oracle-L Freelists
> Subject: RE: RAC install on Linux
> In those VM shops where memory is over-subscribed, how do Huge Pages work in terms of locking memory pages so that they cannot be swapped?
> Thanks

Received on Fri Feb 23 2018 - 11:20:36 CET

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