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Home -> Community -> Mailing Lists -> Oracle-L -> RE: SGA info.
Raja:
Let me see if I can explain it.
As Girijan previously explained, some of this extra memory is taken up with the redo log guard pages. Guard pages are one memory protection unit in size and are there to prevent Oracle software bugs or hackers from corrupting the log buffer.
Another portion of the memory results from a minimum size for the log buffer of 4 * db_block_size. This rounding up is reflected in v$sga, but not in v$sgastat. There is also a lot of "rounding up" and extra memory allocation like this going on with other structures in the sga to fill out full memory pages. This, too, is represented in v$sga, but not in v$sgastat.
The remainder of the space is accounted for in the "empty pages" like the redo log buffer's guard pages that enclose various sga structures to avoid areas stepping on each other. These "empty pages" are also not accounted for in v$sgastat.
HTH, Jon Walthour
-----Original Message-----
Luthra
Sent: Sunday, August 12, 2001 10:41 PM
To: Multiple recipients of list ORACLE-L
Hello,
Doing select * from v$sga shows:-
NAME VALUE -------------------- ---------- Fixed Size 67688 Variable Size 18042880 Database Buffers 16777216 Redo Buffers 172032
What do you mean by "presence of 2 guard pages for the log buffer"?
Please explain.
rgds,
raja
-- On Sun, 12 Aug 2001 17:50:21 Girijan Puthran wrote:Received on Sun Aug 12 2001 - 22:06:13 CDT
>
>Raja,
> 16k of this difference might be with respect to the log buffer
>size (most probably) and this is due to the presence of 2 guard pages
>for the log buffer on some Operating systems, and as for the remaining
>space--I am not too sure.
>
>
> Girijan
>
>
>---------------------------------------- Message History
>----------------------------------------
>
>
>
>Please respond to ORACLE-L_at_fatcity.com
>
>To: ORACLE-L_at_fatcity.com
>cc:
>
>
>
> Hello,
>
>I am running oracle 8.1.5.0.0 on hp11.
>
>If I select from V$sga I get at least 18104 more than what I see in
>v$sgastat. Therefore I wanted to know why the figures are different and
>what statistic in v$sgastat is not counted, and therefore the figure in
>v$sgastat is low??
>
>I am getting some thing like this:-
>
>select sum(value) from v$sga;
>
>35059816
>
>select sum(bytes) from v$sgastat;
>
> 35041712
>
>Please comment if you can, thanks in advance.
>
>rgds,
>
>raja
>--
>
>On Thu, 09 Aug 2001 10:25:21
> Seema Singh wrote:
>>Hermanto
>>which version of oracle u r running?Just see following output
>>SVRMGR> connect internal;
>>Connected.
>>SVRMGR> select sum(value) from v$sga;
>>SUM(VALUE)
>>----------
>>1033101472
>>1 row selected.
>>SVRMGR> select sum(bytes) from v$sgastat;
>>SUM(BYTES)
>>----------
>>1033044248
>>1 row selected.
>>SVRMGR> show sga
>>Total System Global Area 1033101472 bytes
>>Fixed Size 73888 bytes
>>Variable Size 537395200 bytes
>>Database Buffers 491520000 bytes
>>Redo Buffers 4112384 bytes
>>If u see all three output you can see the diffrence.The correct view
>>to check size of sga is v$sga. Hope this will help u.
>>Thanks
>>-Seema
>>
>>
>>
>>>From: Hermanto P <hermanto_p_at_aprilasia.com>
>>>Reply-To: ORACLE-L_at_fatcity.com
>>>To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>>>Subject: RE: SGA info.
>>>Date: Wed, 08 Aug 2001 20:51:10 -0800
>>>
>>>Raja,
>>>if i do what you do..the value is same.
>>>i am not sure if you said the value between v$sgastat and v$sga is
>>>different.
>>>
>>>SVRMGR> select sum(value) from v$sga;
>>>SUM(VALUE)
>>>----------
>>> 64046072
>>>1 row selected.
>>>SVRMGR> select sum(bytes) from v$sgastat;
>>>SUM(BYTES)
>>>----------
>>> 64046072
>>>1 row selected.
>>>SVRMGR>
>>>
>>>Warm Regards,
>>>
>>>Hermanto P
>>>Application Engineer
>>>PT Riau Andalan Pulp And Paper - IT/IS Dept.
>>>Phone : (0761) - 491147 / 491354
>>>HP : 0812-752-3092
>>>"Dream as if you'll live forever, live as if you'll die today"
>>>
>>>
>>>
>>>
>>>-----Original Message-----
>>>Sent: Thursday, August 09, 2001 11:30 AM
>>>To: Multiple recipients of list ORACLE-L
>>>
>>>
>>>Hello gurus,
>>>
>>>I am not able to understand 1 thing:-
>>>
>>>1. If I do :-
>>>
>>>select sum(bytes) from v$sgastat;
>>>it gives me the SGA as :- 35041712
>>>
>>>2. But if I do :-
>>>
>>>select sum(value) from v$sga I get:- 35059816
>>>
>>>There is a difference of 18104 between 2 figures.
>>>
>>>Which 1 should I trust? which gives me the correct value of SGA?
>>>
>>>thanks
>>>
>>>rdgs,
>>>
>>>raja
>>>
>>>
>>>Get 250 color business cards for FREE!
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>>
>>
>>_________________________________________________________________
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>>Please see the official ORACLE-L FAQ: http://www.orafaq.com
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>> INET: oracledbam_at_hotmail.com
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>
>
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>Author: Viraj Luthra
> INET: viraj999_at_lycos.com
>
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>Author: Girijan Puthran
> INET: girijan.puthran_at_db.com
>
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Get 250 color business cards for FREE! http://businesscards.lycos.com/vp/fastpath/ -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Viraj Luthra INET: viraj999_at_lycos.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Jon Walthour INET: jonw_at_fuse.net Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
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