Buffer Cache too big?

Hello Oracle community!
I'm having issues because of my current SGA size on a Win 32-bit platform, its measures are normally on 6,811,549,696 bytes. There was another database administrator before me but he left the company, his instructions were that he setup this size because that time RAM memory was not the problem.
The OS' parameters are set to read the entire 8GB RAM.
If I set a SGA_TARGET to around 6GB, will I only have -800mb on my db and no problems at all? Is there any way to check things better than just set a SGA_TARGET and pray?
Thank you very much!

@Elios
Oracle Version 10.2.0.3.0
It's not an OLTP Database.
@mehmet eser
NAME BYTES RESIZEABLE
Fixed SGA Size 1289604 No
Redo Buffers 7098368 No
Buffer Cache Size 6442450944 Yes
Shared Pool Size 343932928 Yes
Large Pool Size 8388608 Yes
Java Pool Size 8388608 Yes
Streams Pool Size 0 Yes
Granule Size 8388608 No
Maximum SGA Size 6811549696 No
Startup overhead in Shared Pool 268435456 No
Free SGA Memory Available 0
11 rows selected
NAME VALUE
Fixed Size 1289604
Variable Size 360710780
Database Buffers 6442450944
Redo Buffers 7098368
4 rows selected
To use more than the basic on 32bit Windows I used /PAE on boot.ini.

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Buffers/cache too big?

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Will I increase my Buffer Cache ?

Oracle 9i
Shared Pool 2112 Mb
Buffer Cache 1728 Mb
Large Pool 32Mb
Java Pool 32 Mb
Total 3907.358 Mb
SGA Max Size 17011.494 Mb
PGA
Aggregate PGA Target 2450 Mb
Current PGA Allocated 3286059 KB
Maximum PGA Allocated (since Startup) 3462747 KB
Cache Hit Percentage 98.71%
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Two things stand out:
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How many processes are allowed to connect to the database ? (You ought to allow about 2Mb - 4Mb per process to the pga_aggregate_target for OLTP) and at least 1Mb per process for the buffer cache.
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A simple response to your original question would be that you probably need to increase the pga_aggregate_target, and you might as well increase the buffer size since you seem to have the memory for both.
On the downside, changing the pga_aggregate_target could cause some execution plans to change; and changing the buffer size does change the limit size on a 'short' table, which can cause an increase in I/O as an unlucky side effect if you're a little heavy on "long" tablescans.
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Hi Guru(s),
Please anyone can tell me that, how can we check the size of data buffer cache.
Please help.
Regards,
Rajeev K

Hi,
Here is what I would do:
First, let's have a look what views we have available to us
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TABLE_NAME
DBA_HIST_SGA
DBA_HIST_SGASTAT
DBA_HIST_SGA_TARGET_ADVICE
V$SGA
V$SGAINFO
V$SGASTAT
V$SGA_CURRENT_RESIZE_OPS
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V$SGA_RESIZE_OPS
V$SGA_TARGET_ADVICE
GV$SGA
GV$SGAINFO
GV$SGASTAT
GV$SGA_CURRENT_RESIZE_OPS
GV$SGA_DYNAMIC_COMPONENTS
GV$SGA_DYNAMIC_FREE_MEMORY
GV$SGA_RESIZE_OPS
GV$SGA_TARGET_ADVICE
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SQL> desc v$sgainfo
Name                                                              Null?    Type
NAME                                                                       VARCHAR2(32)
BYTES                                                                      NUMBER
RESIZEABLE                                                                 VARCHAR2(3)And how many rows are in it?
SQL> select count(*) from v$sgainfo;
COUNT(*)
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Suggest buffer cache size check

Hi experts,
please suggest how much give size of buffer cache. please tell me how to calculate this.
Note: on database running huge select with where clause.
>
SQL> show sga
Total System Global Area 536870912 bytes
Fixed Size 1220408 bytes
Variable Size 117440712 bytes
Database Buffers 411041792 bytes
Redo Buffers 7168000 bytes
>
>
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SQL> column c4 heading 'Estd Phys| Reads' format 999,999,999,999
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2 size_for_estimate c1,
3 buffers_for_estimate c2,
estd_physical_read_factor c3,
4 5 estd_physical_reads c4
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9 name = 'DEFAULT'
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11 block_size = (SELECT value FROM V$PARAMETER
12 WHERE name = 'db_block_size')
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13 14 advice_status = 'ON';
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Cache Size (m) Buffers Read Factor Reads
36 4,491 1.02 1,768,088,631
72 8,982 1.01 1,751,858,036
108 13,473 1.01 1,745,807,886
144 17,964 1.00 1,742,684,545
180 22,455 1.00 1,740,606,287
216 26,946 1.00 1,739,127,030
252 31,437 1.00 1,737,935,545
288 35,928 1.00 1,736,936,513
324 40,419 1.00 1,736,098,119
360 44,910 1.00 1,735,368,624
Estd Phys Estd Phys
Cache Size (m) Buffers Read Factor Reads
392 48,902 1.00 1,734,775,608
396 49,401 1.00 1,734,701,493
432 53,892 1.00 1,734,086,804
468 58,383 1.00 1,733,466,505
504 62,874 1.00 1,732,871,083
540 67,365 1.00 1,732,300,725
576 71,856 1.00 1,731,737,930
612 76,347 1.00 1,731,204,779
648 80,838 1.00 1,730,669,455
684 85,329 1.00 1,730,117,349
Estd Phys Estd Phys
Cache Size (m) Buffers Read Factor Reads
720 89,820 .98 1,703,583,925
21 rows selected.
Dictionary Cache Hit Ratio : 99.92% Value Acceptable.
Library Cache Hit Ratio : 98.22% Increase SHARED_POOL_SIZE parameter to bring value above 99%
DB Block Buffer Cache Hit Ratio : 60.53% Increase DB_BLOCK_BUFFERS parameter to bring value above 89%
Latch Hit Ratio : 99.72% Value acceptable.
Disk Sort Ratio : 0.00% Value Acceptable.
Rollback Segment Waits : 0.00% Value acceptable.
Dispatcher Workload : 0.00% Value acceptable.
>
Edited by: 928992 on Oct 18, 2012 2:31 PM
Edited by: 928992 on Oct 18, 2012 3:04 PM

I am displaying you mine test db's buffer cache size : (11.2.0.1 on Windows box)
SQL> show parameter db_cache_size;
NAME                                 TYPE        VALUE
db_cache_size                        big integer 0
SQL> select name, current_size, buffers, prev_size, prev_buffers from v$buffer_pool;
NAME                 CURRENT_SIZE    BUFFERS PREV_SIZE PREV_BUFFERS
DEFAULT                       640      78800          0            0
SQL> select name,bytes from v$sgainfo where name='Buffer Cache Size';
NAME                                  BYTES
Buffer Cache Size                 *671088640*
SQL> show sga;
Total System Global Area 1603411968 bytes
Fixed Size                  2176168 bytes
Variable Size             922749784 bytes
*Database Buffers          671088640 bytes*
Redo Buffers                7397376 bytes
SQL> select * from v$sga;
NAME                      VALUE
Fixed Size              2176168
Variable Size         922749784
*Database Buffers      671088640*
Redo Buffers            7397376
SQL> show parameter sga_target;
NAME                                 TYPE        VALUE
sga_target                           big integer 0
SQL>Regards
Girish Sharma
Edited by: Girish Sharma on Oct 18, 2012 2:51 PM
Oracle and OS Info added.

Buffer cache size

Hi there,
Can anyone explain these results on a 10.2.0.1 database?
SQL> select name, bytes/1024/1024 from v$sgainfo where name='Buffer Cache Size';
NAME BYTES/1024/1024
Buffer Cache Size 1728
SQL> show parameter db_cache_size
NAME TYPE VALUE
db_cache_size big integer 768M
NAME TYPE VALUE
sga_target big integer 0
As you can see AMM is disabled (sga_target=0), however v$sgainfo and dba_hist_sga record always a buffer cache size of 1728 MB and db_cache_size is set to 768 MB.
How can it be?
Many thanks.

I answer myself:
db_8k_cache_size big integer 160M
db_cache_size big integer 768M
db_keep_cache_size big integer 400M
db_recycle_cache_size big integer 400M
I am like a newbee...

ASM Buffer Cache - which parameter is responsible for this?

Env: Oracle 10.2.0.4.0 on Windows 2003 R2 32 bit
In one of my testing databases, I saw this. Rest all databases (development and testing) do not have the component "ASM Buffer Cache".
SQL> select component, current_size, user_specified_size from v$sga_dynamic_components;
COMPONENT                          CURRENT_SIZE USER_SPECIFIED_SIZE
shared pool                         553,648,128         209,715,200
large pool                            4,194,304                   0
java pool                             4,194,304                   0
streams pool                                  0                   0
DEFAULT buffer cache                360,710,144         314,572,800
KEEP buffer cache                             0                   0
RECYCLE buffer cache                          0                   0
DEFAULT 2K buffer cache                       0                   0
DEFAULT 4K buffer cache                       0                   0
DEFAULT 8K buffer cache                       0                   0
DEFAULT 16K buffer cache                      0                   0
DEFAULT 32K buffer cache                      0                   0
ASM Buffer Cache                              0         314,572,800I am not able to figure out from the component "ASM Buffer Cache" is coming in this list. Current_size is zero so its not of a concern actually but I was wondering which parameter enforces this value.
Can anybody shed some light on this?
Regards,
Message was edited by:
Satish Kandi
Forgot to mention that we are not using ASM at all.

I have some databases running on 10.2.0.3.0 (testing + dev) and others on 10.2.0.4.0 (dev databases) and I can see this component in all of them.
I have no databases running at earlier versions of 10g so cannot confirm if it was there earlier too.
With your hint of 11g in mind, I searched 11g documentation too and could not find any references to this component.

Buffer cache hit ration found 99.7%,still the app users complains.

Here in my database,i querey the v$sysstat and found the buffer cache hit ration 99.7% ,by looking that hit ration there is room improvements.
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hare krishna
Alok

As others have said, buffer cache hit ratio is only one of the measurements - and it is often improperly applied, making it worse than useless.
Since this is in production,. it's too late to do anything about the design. So we skip that very important step and go to the SQL statements ...
What are the users complaining about, in detail? Is it the system, or is it a specific operation? Use that knowledge to attempt to define a single SQL statement or a small set of SQL statements, and then start tuning those.
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Buffer Cache too big?

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