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DB_KEEP_CACHE_SIZE

Posted on 2006-06-08
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Last Modified: 2008-01-09
Hi all,
My DB_KEEP_CACHE_SIZE is 117440512. However, the total size of objects cached in this buffer is 430669824. Where is this Keep buffer getting this extra space? Does this buffer borrow space from somewhere else when needed?

SQL> show parameter db_keep_cache_size;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_keep_cache_size                   big integer 117440512

SQL> select  buffer_pool, sum(blocks)*8192
from dba_segments
where buffer_pool != 'DEFAULT'
group by  buffer_pool;  
BUFFER_ SUM(BLOCKS)*8192
------- ----------------
KEEP           430669824
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Question by:jkopoku
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Expert Comment

by:actonwang
ID: 16862930
BLOCKS field means size, in Oracle blocks, of the segment. It is not the size of BUFFER_POOL.

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Author Comment

by:jkopoku
ID: 16863156
I am dividing the sum of blocks in the KEEP POOL by the block size. This will give me the total size of segments in the KEEP POOL. I don't undersatnd why the total size of segments in the KEEP POOL is bigger than the   DB_KEEP_CACHE_SIZE .
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Expert Comment

by:actonwang
ID: 16863221
DB_KEEP_CACHE_SIZE defines count or size of keep cache size.

BUFFER_POOL in each segment suggests it should be kept in buffer when it is accessed.
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Author Comment

by:jkopoku
ID: 16863471
So when I issue the command "alter table emp storage( buffer_pool keep);" the emp table is not actually cache in the KEEP BUFFER POOL, but suggest it should be kept in it when it is accesed. Is that what you are saying?
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actonwang earned 400 total points
ID: 16863630
yes. BUFFER_POOL parameter of the STORAGE clause specified the area of the database buffer cache to keep the blocks of the table when read from the data file while querying for update/delte.
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Author Comment

by:jkopoku
ID: 16863908
Thanks for your help.
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Expert Comment

by:actonwang
ID: 16864045
for side note:

blocks column in dba_segments table is total blocks for this object not used block. You need to look at the blocks column in the dba_tables after you run the statistics.

also, just as you know, objects in the KEEP buffer pool runs are still can be aged out. It still has LRU list.

acton
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Expert Comment

by:actonwang
ID: 16864051
though you need to read oracle performance document to get a big picture, but the following link will give you a quick good  feel:

http://asktom.oracle.com/pls/ask/f?p=4950:8:480502720606439489::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:253415112676
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