Re: ORACLE 9i - memory usage
- From: "ORA600" <panandrao@xxxxxxxxx>
- Date: 30 May 2006 23:08:05 -0700
Hi,
Apologies if this is a double post...something wrong with usenet..
I would say that Oracle has to allocate or "occupy" or reserve 20GB of
virtual address space from the OS since you have explicitly set that
value for sga_max_size.
Oracle allocates 13GB (which is the total size of your SGA) at startup
and then allocate the rest of the 7GB on demand when you resize your
SGA.
20GB is therefore reserved within the virtual address space and since
the physical memory has not yet been allocated, 20GB will not show up
within physical memory. It will ONLY show up in virtual memory address
space.
Only 13GB of shared memory is occupied at start. no other external
process will be able to address any part of this 20GB memory since it
is owned by Oracle.
This is why you see a single 13GB shared memory segment with your ipcs
command. Whenever you want to increase the SGA size, Oracle can do so
by bringing in the required memory into its physical address space.
Without this "reserve" feature, there wouldn't be any point in having a
sga_max_size.
On HPUX, glance tool can show you the process address space. it should
be visible from there. i can't remember the HPUX equivalent of pmap...
What does this query show you?
select * from v$SGA_DYNAMIC_FREE_MEMORY
the output must show approximately 7GB of space available for
expansion.
Why don't you try expanding the db_cache_size by another 6GB and see
the results?
that should clearly give you the answer...
hope that helps.
cheers
anand
Dave wrote:
Thanks to all for attending this discussion.
Firstly let me add some information...
ipcs shows me the shared segment for this db:
m 826383 0x43fe1ba4 --rw-rw---- oracle dba 12903632896
show sga shows me it is the same than sga:
Total System Global Area 1.2887E+10 bytes
Fixed Size 754680 bytes
Variable Size 6492782592 bytes
Database Buffers 6392119296 bytes
Redo Buffers 1167360 bytes
1) Can I guess it is actually allocating 13Gb of memory?
Jagjeet, your tip related to 9i limitation is Very interesting:
unfortunately the Oracle note you mentioned is related to Solaris (I am
working with hpux 11.11) and it does not apply to 9.2 (I have 9.2.0.7).
I have tried without success to find in metalink something related to
hpux: do you have information about the same problem on this OS ?
2) A correct way to confirm if my db is allocating the sga or the
SGA_MAX_SIZE of memory could be to check how much memory is actually
allocating.
What is the correct way to evaluate the current memory used by an
instance?
Looks like V$PROCESS does not give the correct picture:
pga_used_mem = 17298780
pga_alloc_mem = 119051092
Thank you again,
Dave
.
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- Re: ORACLE 9i - memory usage
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