SGA, PGA and... little extra?

Will oracle process use some extra "non oracle" memory for OS related stuff?
Mean, not considering SGA, I connect a database process and I see:
SQL> select p.program,
2 p.spid, pm.category, pm.allocated/1024 allocated, pm.used/1024 used, pm.max_allocated/1024 max_allocated
3 from V$PROCESS p, V$PROCESS_MEMORY pm
4 where p.pid = pm.pid
5 and p.spid =2650;
                                                                                                        Max
                                                                          Allocated       Usedd   allocated
PROGRAM                        SPID                     CATEGORY                 Kb          Kb          Kb
oracle@uxlabhost11             2650                     SQL                      14           9          42
oracle@uxlabhost11             2650                     PL/SQL                   56          34          57
oracle@uxlabhost11             2650                     Other                  1501                    1501That's allocated PGA after having connected and done nothing else
So it somehow allocated 1.4 Mb upon start-up...
Now question is. Do oracle processes use OS memory which cannot be considered as SGA or PGA?
Reason being my trying to estimate memory needs for a database server. Many I've read correct formula should be SGA + max allocated PGA + some_extra_just_in_case...
Is there an estimate on how much that "some_extra_just_in_case" would be per process?
If OS dependent, I'm implementing on RHEL 6...
thanks

So, I've used pmap...
Got 257 enties in the form "4096K rw-s- /dev/shm/"
since we are using AMM , that should do for PGA and SGA ... some 1052672 Kb, which process is attached to...
yet pmap then continues to display other entries....
0000002a95557000      4K r-x-- /opt/oracle/product/11g/lib/libodm11.so
0000002a95558000   1024K ----- /opt/oracle/product/11g/lib/libodm11.so
0000002a95658000      4K rw--- /opt/oracle/product/11g/lib/libodm11.so
0000002a95659000      4K rw---    [ anon ]
0000002a9565a000    392K r-x-- /opt/oracle/product/11g/lib/libcell11.so
0000002a956bc000   1024K ----- /opt/oracle/product/11g/lib/libcell11.so
0000002a957bc000     40K rw--- /opt/oracle/product/11g/lib/libcell11.so
0000002a957c6000      4K rw---    [ anon ]
0000002a957c7000    864K r-x-- /opt/oracle/product/11g/lib/libskgxp11.so
.. TRUNCATED...
0000003fb810a000     64K rw---    [ anon ]
0000003fbbd00000     84K r-x-- /lib64/libnsl-2.3.4.so
0000003fbbd15000   1020K ----- /lib64/libnsl-2.3.4.so
0000003fbbe14000      4K r---- /lib64/libnsl-2.3.4.so
0000003fbbe15000      4K rw--- /lib64/libnsl-2.3.4.so
0000003fbbe16000      8K rw---    [ anon ]
0000007fbffde000    136K rwx--    [ stack ]
ffffffffff600000      4K r-x--    [ anon ]
total          1276452KNotice "total 1276452K"
So you saying non SGA/PGA would be 1276452 - 1052672?
That would be too much... yet if pmap another process, almost all flags (hex column) but [ stack ] are the same....
So how to tell which of those are shared and which are "exclusive" to the process, i.e: The "some extra just in case" mem...
thanks

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Hi
I am new to Oracle server architecture.
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As per my understanding, the data that we retrieve from a SQL query is stored in SGA in Database buffer cache.
I have some queries:
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Thanks
Abhi

AB312062 wrote:
Hi
I am new to Oracle server architecture.
Please correct me if am wrong.
As per my understanding, the data that we retrieve from a SQL query is stored in SGA in Database buffer cache.
I have some queries:
1. Does the database buffer cache store only data from SQL queries or anything else also? What is its size? Can we set the size?
2. Where are the parsed SQL queries stored - SGA or PGA? And where exactly? I want to know if all the users connected in an Instance have access to each other's parsed SQL queries?
3. SGA is shared by all users in an Oracle Instance? PGA and UGA are local to a specific user in an instance? Is it correct?
Thanks
AbhiThe questions you have are all good ones, but require far too much to be explained (properly) in a forum such as this.
I would highly recommend picking up a book by Tom Kyte and reading through that.
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SGA, PGA and SHMMAX Setting

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The SHMMAX parameter is used to define the maximum size (in bytes) for a shared memory segment and should be set large enough for the largest SGA size.
http://www.idevelopment.info/data/Oracle/DBA_tips/Linux/LINUX_8.shtml
http://books.google.co.in/books?id=2ImPFP6Yk64C&pg=PA357&lpg=PA357&dq=PGA+is+included+in+SHMMAX&source=bl&ots=On3S7-CEX0&sig=LhOYOO946hrPZh-cIUEzWNiwpRg&hl=en&ei=xyLOTJqaC4yYvAONm7T3Dw&sa=X&oi=book_result&ct=result&resnum=5&ved=0CCwQ6AEwBA#v=onepage&q&f=false
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922884 wrote:
Hi,
Thanks for your repsonse.
Architect asking that.
Can i use DBA_HIST_SGA ,DBA_HIST_SGAstat for sga and DBA_HIST_TBSPC_SPACE_USAGE ,DBA_HIST_TABLESPACE_STAT for tablespace.
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I have a plan to increase size of PGA and SGA. Please recommend me which metric in Statspack report I should monitor to check what is the impact of such change.
Best.

Hi Lesak;
Please check below 2 thread:
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Re: Estimating SGA Size
SGA and PGA size
SGA and PGA size
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Difference between UGA, PGA and SGA in oracle

please tell me what is the difference between UGA, PGA and SGA in oracle in the simple layman language
thanx in advance

UGA
The User Global Area (UGA) is a memory area (RAM) that holds session-based information.
Shared Server Area
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Dedicated Server
When running in [[Dedicated Server]] mode (one session = one dedicated process), the UGA is stored in the [[PGA]] (process global area).
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What is the diffrence between PGA and UGA?

Hi All
Just one question
"What is the diffrence between PGA and UGA?"
Thanks

PGA Memory
The Program Global Area (PGA) is a memory region that contains data and control information for a single process (server or background). The PGA is made up of the following:
Stack Space
A PGA always contains a stack space, which is memory allocated to hold a session's variables, arrays, and other information.
Session Information - (UGA)
A PGA in an instance running without the multi-threaded server (named Shared Server in Oracle9i) requires additional memory for the user's session, such as private SQL areas and other information. If the instance is running the multi-threaded server, this extra memory is not in the PGA, but is instead allocated in the SGA (the Shared Pool).
Shared SQL Areas
Shared SQL areas are always in shared memory areas of the SGA (not the PGA), with or without the multi-threaded server.
Non-shared and Writable
The PGA is a non-shared memory area to which a process can write. One PGA is allocated for each server process; the PGA is exclusive to a server process and is read and written only by Oracle code acting on behalf of that process.
UGA Memory
The UGA, or User Global Area, is allocated in the PGA for each session connected to Oracle in a dedicated server environment. The PGA is memory allocated at the client to hold a stack which contains all of the session's variables, etc. In a Shared Server environment, Oracle allocates this memory in the Shapred Pool (the shared pool is contained in the SGA), for all sessions. This helps to reduce the PGA (client) memory footprint of Oracle, but will increase the SGA (shared pool) requirements.

SGA/PGA best practice

With an XE limitation of 1GB for the PGA and SGA, how would one best preserve this limitation?
In other words, how would one minimise the PGA and SGA usage via ones interface with Oracle?
For instance, in a SQL query I was building I could either (The query has multiple aggregates on multiple tables in a 'one to many' join relationship):
1) Use WITH clauses
2) Use inline views
3) Use standard views
4) Use temporary tables
5) Maybe more possibilities
Without much of an insite into how Oracle 'works' it's difficult to gauge which of these is less 'resource hungry'.
Possibly there is a reference on how to use the PGA & SGA efficiently?
Or possibly a more definitive explanation on what's actually stored in these memory areas (rather than just 'prorgam' and 'system' data).
Regards all,

SGA is used in 2 main areas: parsing the SQL and avoiding disk reads by having stuff in memory. There is one SGA for all of XE instance.
PGA is used heavily for sorting, hash joining and 'working stuff'. The PGA is created for each Dedicated Server process. Much of the PGA is inside the SGA for Shared Server processes
SGA: (There are exceptions to each of these 'Rules Of Thumb' or 'ROT' statements)
Good coding technique will allow reuse of SQL and avoid as much as possible reparsing;
Use bind variables;
Do not create SQL on the fly;
Avoid dynamic SQL (concat strings to create SQL on the fly);
Forget about tweakiing the buffer cache as it is mainly a performance thing that you can't do much about in XE;
WITH clause is nice as it may reduce the count of subqueries;
Leave it with 'automatic memory management' (again a perf hit, but it will attempt to optimize mem availability);
Don't reinvent - Use the features that are loaded as they will likely get statements out faster, releasing memory faster;
Stored Views may (often do) grab unneeded table data. When joining to stored views, see whether they can be replaced by cleaner code;
Do not create SQL on the fly.
PGA:
Use shared server when feasible (at risk of performance hit);
Global Temp Tables go into PGA, watch the use;
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SGA/PGA (Memory) in RAC environment.

Guys,
I would like to get your inputs on SGA / PGA settings on a RAC database.. Does LMS/LMON/LMD process use memory which is part of PGA or these process allocate memory at OS level ?
I would like to see the usage of Memory used by a database.
below sql from Mr. Kyte's website i have used. Somehow i am not getting real usage of the system. Any help would be appreciated.
Thanks
select
ssst.sid,
stn.name ,
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OSUSER,
MACHINE,
TERMINAL,
PROGRAM ,
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order by 3 asc ;
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From sql script, that get "session pga memory","session pga memory max" each of session in oracle database(on that node)
You'll see
sid: session id
memory:
if "session pga memory" = pga memory in this session now
if "session pga memory max"= maximum pga memory in this session.
program: os program name
More deatails abour v$session http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/dynviews_2088.htm#REFRN30223
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round(sum(ssst.value)/1024/1024,2) memory
from v$statname stn,v$sesstat ssst , v$session ses
where stn.STATISTIC# = ssst.STATISTIC# and
ssst.sid = ses.sid and
name ='session pga memory';
"session pga memory max":
select
round(sum(ssst.value)/1024/1024,2) memory
from v$statname stn,v$sesstat ssst , v$session ses
where stn.STATISTIC# = ssst.STATISTIC# and
ssst.sid = ses.sid and
name ='session pga memory max';
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COLUMN username FORMAT A20
COLUMN module FORMAT A20
SELECT a.inst_id,
NVL(a.username,'(oracle)') AS username,
a.module,
a.program,
Trunc(b.value/1024) AS memory_kb
FROM gv$session a,
gv$sesstat b,
gv$statname c
WHERE a.sid = b.sid
AND a.inst_id = b.inst_id
AND b.statistic# = c.statistic#
AND b.inst_id = c.inst_id
AND c.name = 'session pga memory'
AND a.program IS NOT NULL
ORDER BY b.value DESC;

Oracle 11g SGA & PGA setup

Hi I installed oracle 11g & create database , now i want to use fully optimize database.
Currently my DB server RAM is 16GB, how should i allocate SGA for this.If i used oracle 11g automatic memeory management feature to allocate SGA+PGA, how should i use them.Currentlymy SGA is set to 4GB, Please advise

Hi,
It is depends upon the workload which you have in your organization(future and present situation)
SGA+PGA size will be automatically managed by Oracle. No need to worry about this.
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Thanks

AWR SGA+ PGA usage

Hi
We're doing some performance testing on our database. The SGA is set to 1.5GB and PGA set to 0.5GB. At some point we are runnning out of memory as we ramp up the number of users and transactions .
What I'm looking for is to graph the PGA and SGA usage seperately regular intervals (a line graph) showing their increaase as users ramp up.
Anyone any ideas on how I can get this information whether through AWR or manually.
Thanks in advance.

You have not posted the version you are on. You should use automatic pga management and unset the values for areasize parameters (if there is no specific reason for keeping them).
ORA-04030: out of process memory when trying to allocate 8389132 bytes (pga heap,redo read buffer)
Doing block recovery for file 3 block 76812
Resuming block recovery (PMON) for file 3 block 76812What are the OS level statistics of memory usage ?
It simply means that Oracle (rather OS...as Oracle is also going to request memory from OS only) is running out of memory. Most common reason behind that is use of features like bulk collect without any limit clause which causes the pga memory to grow beyond pga_aggregate_target...and finally sucking all the memory available. Further requests for memory allocation start failing with ORA-04030.
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Edited by: amardeep.sidhu on Nov 24, 2010 9:29 AM

SGA & PGA target

Hi all,
My questions is regarding how to set up SGA & PGA target values giving DB server is MS 2003 Enterprise 64 edition sever with 63 GB of RAM. Our DB’s version is 10.2.0.3 and RACed with 2 instances.
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I would like to know if there is any rule(s) that SGA can’t be more than certain percentage of total RAM for the server.
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Have a great weekend!!
Shirley

Hi
Here is my approach:
1) consider free physical memory (meassure must be taken with Oracle down)
2) substract a 10% of that amount as a margin
3) if the box is exclusive for Oracle, the remaining amount may be your SGA+PGA limit
4) if not is exclusive, then substract memory required for other services, then you'll get the SGA+PGA limit.
5) Substract your PGA size, giving the SGA figure
For instance
59 Gb - 6 Gb = 53 Gb - 4 Gb = 49 Gb
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Setting PGA+SGA beyond the free physical memory figure, may lead to swaping and degraded system performance.
Regards
http://oracledisect.blogspot.com

Reg:-SGA & PGA Memory Allocation Size

Hi all
I Have a server System Configuration with
RAM size: 16GB Ram & Hard disk Size of 1TB.
I Installed Oracle 11g R2 in the server System
I want to Allocate Dedicated Memory for oracle..
How Should i calculate the Memory size of SGA+PGA for good Performance..

Check MOS
*How to calculate the memory used by dedicated and shared servers? [ID 551415.1]*

SGA & PGA concept

We have a production Oracle 11g DB in which SGA_TARGET is 0 but ASSM is enabled but the documentation on Oracle says that if SGA_TARGET is 0 means that ASSM is disabled. Also, PGA_AGGREGATE_TARGET is 0 but Maximum PGA allocated is around 1 GB.
I hope, my question is clear that concept seems to be confusing where SGA_TARGET is 0 but ASSM is enabled and also PGA_AGGREGATE_TARGET is 0 but maximum PGA allocated is 1 GB.
Please revert with the reply to my query.
Regards

972145 wrote:
Thanks for your reply but there is some confusion. ASMM is automatic shared memory management which seems to be similar to AMM which is automatic memory management. ASMM can be seen from OEM under Database Configuration->Memory Advisors. I guess, there is ASM which is automatic storage management to do with reduntant copies of data to provide fault tolerance.
ASMM - 10g setting for the automatic SGA using the parameter sga_target .
AMM - 11g setting for both SGA and PGA, uses the parameter memory_target
ASM - Automatic Storage Management, nothing to do with SGA or PGA
ASSM - Automatic Segment Space Management, for the tables and nothing to do with the PGA and SGA
Aman....
Edited by: Aman.... on Jan 21, 2013 3:53 PM corrected the typo

SGA, PGA and... little extra?

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