[askdba] Re: Question regarding MAX SGA Size and Physical Memory

  • From: "Yavor Ivanov" <yavor_ivanov@xxxxxxxx>
  • To: askdba@xxxxxxxxxxxxx
  • Date: Tue, 26 Oct 2004 08:57:15 +0300

        First of all, if you have 4 GB RAM you can easily use 3 GB for Oracle  
(Note:1036312.6). In fact, you can use even more with AWE (Note:225349.1),  
but in your case it is not needed.

        1. If your process space is limited to 2 GB (and it is, if you do net 
the 3 GB switch of Windows), you cannot have 2 GB SGA. Your _whole_  
process space is 2 GB. This is SGA + PGA + Oracle executables and  
libraries (~50 MB). And, in fact, Windows reserves the first and last 64 K  
of that 2 GB windows to catch bad pointers. So you never have exact 2 GB.  
Remember, the SGA is allocated in granules (16 MB each, in your case), so  
you cannot allocate (2GB - 128K)

        2. No. Note 148495.1 statеs:
"At instance startup the Oracle Server allocates the granule entries, one  
for each granule to support SGA_MAX_SIZE bytes of address space."
        So Oracle will try to allocate 2 GB, no matter if you use 128 MB or 2 
for all pools.


On Mon, 25 Oct 2004 17:07:32 -0400, Rajesh Puneyani  
<rajpuneyani@xxxxxxxxx> wrote:

> Hi guys,
> We are on windows 2k / oracle 9iR2.
> One of my database has following configuration -
> SGA_MAX_SIZE = 550 Mb
> SIZE of SGA = 550 Mb
> This has to be a dedicated database on this server (with 4Gb RAM). so
> whole 2Gb can be dedicated to this one database.
> 1. Now If I shutdown this database, change the parameter SGA_MAX_SIZE
> = 2Gb then can I expect any issues while restarting the database ?
> 2. If LOCK_SGA is false then Step 1 would not have any effect on
> ACTUAL SGA Size..Right ? Pls. confirm.
> Your insight on this would be highly appreciated.
> Thanks and Regards
> Rajesh

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