Re: AW: AW: SGA_MAX_SIZE vs. SGA_TARGET

  • From: Neil Chandler <neil_chandler@xxxxxxxxxxx>
  • To: "Markus.Zwettler@xxxxxxxxxx" <Markus.Zwettler@xxxxxxxxxx>
  • Date: Mon, 7 Sep 2015 15:45:29 +0100

No AMM is a good thing IMHO. The algorithms suck and really overstate the
shared pool, hugely over time.

One of the main reasons for using large pages in Linux is to stop the use of
AMM (that, and performance of course). I've never seen AMM work nicely. Put the
effort in, configure your systems optimally.

How often do you change your SGA in Production? Once a year? Every 5 years?

Regs

Neil.
sent from my phone

On 7 Sep 2015, at 15:34, Zwettler Markus (OIZ) <Markus.Zwettler@xxxxxxxxxx>
wrote:

I didn’t try large pages either as we have several small instances per
partition.

Large pages would mean no AMM, no manual resize without reboot, large pages
recalculation + reconfigure on each change,… Too much effort I think.

Would be nice to see some testcases. J

Markus


Von: Neil Chandler [mailto:neil_chandler@xxxxxxxxxxx]
Gesendet: Montag, 7. September 2015 16:11
An: Zwettler Markus (OIZ)
Cc: carlospena999@xxxxxxxxx; frits.hoogland@xxxxxxxxx;
oracledbaquestions@xxxxxxxxx; ORACLE-L
Betreff: Re: AW: SGA_MAX_SIZE vs. SGA_TARGET

AIX is flexible if you are using "medium" (64k) pages but not if you are
using pinned 16m large pages.

I've not had any opportunity to compare the performance of each method, so I
can't say which is best under what scenario. Not worked on AIX for 3 years or
so.

Neil.
sent from my phone

On 7 Sep 2015, at 12:45, Zwettler Markus (OIZ) <Markus.Zwettler@xxxxxxxxxx>
wrote:

AIX is flexible.


google “developerworks aix sga_max_size” + see “AIX Performance:
Configuration & Tuning for Oracle & Oracle RAC”, Page 24.


Cheers, Markus



Von: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] Im
Auftrag von Cee Pee
Gesendet: Samstag, 5. September 2015 21:21
An: frits.hoogland@xxxxxxxxx
Cc: oracledbaquestions@xxxxxxxxx; ORACLE-L
Betreff: Re: SGA_MAX_SIZE vs. SGA_TARGET

How does that work in AIX? If SGA_MAX_SIZE is set at 20G and SGA_TARGET is
10G, does it allocate 10G and let it go up and down, up to a maximum of 20G?

Also if SGA_TARGET and SGA_MAX_SIZE are same, lets say 5Gb, then does oracle
guarantee SGA will not take more than 5Gb any time.



On Sat, Sep 5, 2015 at 1:30 PM, <frits.hoogland@xxxxxxxxx> wrote:


Verstuurd vanaf mijn iPad

Op 5 sep. 2015 om 20:07 heeft Dba DBA <oracledbaquestions@xxxxxxxxx> het
volgende geschreven:

Was really getting worried I was senile and was going to start drooling on
myself. I knew I was able to get memory to allocate and deallocate in the
past. It was on Solaris.

Does anyone know why this varies by unix/linux flavor? What is solaris doing
that Linux does not?
Every Unix like platform oracle is on has a HP implementation. Because the
implementation is depended on cpu huge page support and the implementation in
the operating system, you will see changes in how oracle is able to use it,
because it is depended on them.

On Solaris (only I believe) PGA can be allocated in HP.



On Sat, Sep 5, 2015 at 1:54 PM, Neil Chandler <neil_chandler@xxxxxxxxxxx>
wrote:
It depends upon your platform. Most platforms allocate max_size so having a
lower sga_target is pointless and a waste of memory. Some platforms do not
(Solaris), and only allocate sga_target, with max_size an unused top limit.

Neil.
sent from my phone

On 5 Sep 2015, at 18:51, Dba DBA <oracledbaquestions@xxxxxxxxx> wrote:

yeah this is old. I know its on the web. However, the responses I see are
not to the question I have.

What is the point to having two parameters? If SGA_MAX_SIZE reserves memory
for oracle as an upper bound, but would I want to be able to raise and
lower SGA_TARGET? What do I do with the 'spare memory'.
PGA_AGGREGATE_TARGET is separate and not taken from memory reserved with
SGA_MAX_SIZE

db_cache,shared_pool, large_pool,streams, java, etc... all come out of
SGA_TARGET. So what is the point to this? I am missing something.

I have I have 20 GB SGA_MAX_SIZE and a 10 GB SGA_TARGET. What is oracle
doing with the other 10 GB?



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