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Trying to understand how much memory Oracle uses

Posted on 2009-05-01
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Last Modified: 2013-12-18
Hello Experts,
I'm trying to understand how Oracle uses memory.
I have an AIX 5.3 server with 3GB of memory. The sga_max_size for the 10.2.0.4 database is set to 316MB.

The server is only running this one instance, so I'm wondering why is it using 90%+ of its memory?

I assumed that Oracle wouldn't use more than 316MB, but that must not be the case.

The top 30 memory processes are all Oracle.

< > ps auxw | sort -r +3 | head -30
USER         PID %CPU %MEM   SZ  RSS    TTY STAT    STIME  TIME COMMAND
oracle    114700  0.0  4.0 97428 110060      - A      Apr 21  2:53 ora_cjq0_ISDQA
oracle    397546  0.0  4.0 97236 105248      - A      Apr 21  1:58 ora_pmon_ISDQA
oracle    319566  0.0  4.0 95876 108168      - A      Apr 21  1:15 ora_mmon_ISDQA
oracle    495860  0.1  4.0 95644 111584      - A    10:07:43  0:13 oracleISDQA (LOCAL=NO)
oracle    651296  0.0  4.0 95448 105752      - A    13:58:18  0:04 oracleISDQA (LOCAL=NO)
oracle   1126596  0.0  4.0 95248 111188      - A    10:09:49  0:01 oracleISDQA (LOCAL=NO)
oracle    569452  0.0  4.0 95216 105504      - A      Apr 29  0:01 oracleISDQA (LOCAL=NO)
oracle    303286  0.0  4.0 95004 105340      - A      Apr 21  0:30 ora_dbw0_ISDQA
oracle   1093704  0.0  4.0 95000 110940      - A    09:56:06  0:01 oracleISDQA (LOCAL=NO)
oracle   1114356  0.0  4.0 94868 110808      - A    10:21:01  0:00 oracleISDQA (LOCAL=NO)
oracle    659570  0.0  4.0 94764 107556      - A    13:58:18  0:02 oracleISDQA (LOCAL=NO)
oracle    782476  0.0  4.0 94760 105204      - A      Apr 29  0:00 oracleISDQA (LOCAL=NO)
oracle    594010  0.0  4.0 94752 105496      - A      Apr 29  0:00 oracleISDQA (LOCAL=NO)
oracle    618678  0.0  4.0 94500 110440      - A    09:14:17  0:00 oracleISDQA (LOCAL=NO)
oracle    409818  0.0  4.0 94296 105452      - A      Apr 21  0:00 ora_q000_ISDQA
oracle    249966  0.0  4.0 94140 107380      - A      Apr 21  0:36 ora_smon_ISDQA
oracle    274452  0.0  4.0 94096 105324      - A      Apr 21  1:30 ora_ckpt_ISDQA
oracle    561164  0.0  4.0 93320 105092      - A      Apr 21  0:00 ora_d000_ISDQA
oracle    876700  0.0  4.0 92624 105364      - A    13:58:18  0:00 oracleISDQA (LOCAL=NO)
oracle    667710  0.0  4.0 92624 105364      - A    13:58:18  0:00 oracleISDQA (LOCAL=NO)
oracle    778296  0.0  4.0 92624 105300      - A    13:58:17  0:00 oracleISDQA (LOCAL=NO)
oracle    196812  0.0  4.0 92508 105220      - A      Apr 21  0:00 ora_reco_ISDQA
oracle    516204  0.0  4.0 92432 105416      - A      Apr 21  2:48 ora_mmnl_ISDQA
oracle    520362  0.0  4.0 92308 104984      - A      Apr 21  0:01 ora_q001_ISDQA
oracle    573456  0.0  4.0 92272 105092      - A      Apr 21  0:00 ora_s000_ISDQA
oracle    442516  0.0  4.0 92268 104980      - A      Apr 21  0:03 ora_qmnc_ISDQA
oracle    327810  0.0  4.0 92256 105004      - A      Apr 21  0:15 ora_mman_ISDQA
oracle    372940  0.0  4.0 92244 105080      - A      Apr 21  0:14 ora_psp0_ISDQA
oracle    299016  0.0  4.0 107464 105116      - A      Apr 21  0:30 ora_lgwr_ISDQA


Total System Global Area  331350016 bytes
Fixed Size                  2083824 bytes
Variable Size             205521936 bytes
Database Buffers          117440512 bytes
Redo Buffers                6303744 bytes

+-topas_nmon--#=PURR Stats-------Host=basalt---------Refresh=2 secs---11:39.18---
| Memory ------------------------------------------------------------------------
|          Physical  PageSpace |        pages/sec  In     Out | FileSystemCache  
|% Used       91.3%      6.9%  | to Paging Space   0.0    0.0 | (numperm) 41.2%  
|% Free        8.7%     93.1%  | to File System    0.0    6.0 | Process   25.7%  
|MB Used    2805.9MB   567.7MB | Page Scans        0.0        | System    24.4%  
|MB Free     266.1MB  7624.3MB | Page Cycles       0.0        | Free       8.7%  
|Total(MB)  3072.0MB  8192.0MB | Page Steals       0.0        |           ------ 
|                              | Page Faults       0.5        | Total    100.0%  
|------------------------------------------------------------ | numclient 41.2%  
|Min/Maxperm     578MB( 19%)  2312MB( 75%) <--% of RAM        | maxclient 75.3%  
|Min/Maxfree     960   1088       Total Virtual   11.0GB      | User      62.0%  
|Min/Maxpgahead    2      8    Accessed Virtual    1.6GB 14.6%| Pinned    25.5%

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Question by:doberboy
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schwertner earned 2000 total points
ID: 24286743
It is an old story.
Orocle doesn't uses the storage.
The storage is used by AIX as cache. It caches disk sectors, processes, etc. until the storage (I mean the RAM of course is full). But when a real request for storage comes the caches will be immediatelly put on disk and storage will be free.

Years ago we have the same panic. I waste more then one month to understand that this is the expected behavior of Unix/Linux OS systems.

To get a real sight what happend you need more sophisticated tool to watch the RAM. In some Linux distribution it is called xosview, but I do not know how such tool is called in AIX.
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by:schwertner
ID: 24317242
Good luck!
And find the tool that distingiushes cached RAM from used RAM.
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