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Keep Buffer Pool [message #637572]

Wed, 20 May 2015 06:14

fabi88
Messages: 112
Registered: November 2011

Senior Member

Hi,

We create a table and set value buffer mode to "Buffer_Pool_Keep", but do not change default value "DB_KEEP_CACHE_SIZE"(DB_KEEP_CACHE_SIZE=0).
In this situation, does this mean that the keep buffer space can not be used?

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Re: Keep Buffer Pool [message #637573 is a reply to message #637572]

Wed, 20 May 2015 06:21

John Watson
Messages: 9003
Registered: January 2010
Location: Global Village

Senior Member

That is correct. Generally, I wouldn't try to use the keep or recycle pools from 11.x. I think that the buffer cache retention algorithms have been improved sufficiently that Uncle Oracle can now manage the cache better than I can.

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Re: Keep Buffer Pool [message #637575 is a reply to message #637573]

Wed, 20 May 2015 06:22

gazzag
Messages: 1119
Registered: November 2010
Location: Bedwas, UK

Senior Member

Quote:

Uncle Oracle

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Re: Keep Buffer Pool [message #637578 is a reply to message #637572]

Wed, 20 May 2015 06:31

fabi88
Messages: 112
Registered: November 2011

Senior Member

Thank you very much Mr.Watson,

So when value of "DB_CACHE_SIZE" is equal zero(DB_CACHE_SIZE=0) and set value buffer mode to "Default" for any segment(such as table), does this mean that "Database Buffer Cache" can not be used?

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Re: Keep Buffer Pool [message #637580 is a reply to message #637578]

Wed, 20 May 2015 06:48

John Watson
Messages: 9003
Registered: January 2010
Location: Global Village

Senior Member

You need to read up on Automatic Shared Memory Management (ASSM) and Automatic Memory Management (AMM).

--sorry, ASMM, not ASSM

[Updated on: Wed, 20 May 2015 06:54]

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Re: Keep Buffer Pool [message #637588 is a reply to message #637580]

Wed, 20 May 2015 08:47

fabi88
Messages: 112
Registered: November 2011

Senior Member

Thank you.

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Re: Keep Buffer Pool [message #637591 is a reply to message #637578]

Wed, 20 May 2015 09:30

bpeasland
Messages: 51
Registered: February 2015
Location: United States

Member

fabi88 wrote on Wed, 20 May 2015 06:31

Thank you very much Mr.Watson,

So when value of "DB_CACHE_SIZE" is equal zero(DB_CACHE_SIZE=0) and set value buffer mode to "Default" for any segment(such as table), does this mean that "Database Buffer Cache" can not be used?

You can't go without the default Buffer Cache. It must exist. If you have DB_CACHE_SIZE=0, then another parameter (SGA_TARGET? MEMORY_TARGET?) needs to be set. I haven't tested it, but I do leave the possibility that Oracle could have a default value if no parameters are set to size the default Buffer Cache.

Cheers,
Brian

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Re: Keep Buffer Pool [message #637600 is a reply to message #637591]

Wed, 20 May 2015 10:36

Michel Cadot
Messages: 68776
Registered: March 2007
Location: Saint-Maur, France, https...

Senior Member
Account Moderator

Quote:

I haven't tested it, but I do leave the possibility that Oracle could have a default value if no parameters are set to size the default Buffer Cache.

Yes it is explained in the documentation. Wink

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Re: Keep Buffer Pool [message #637902 is a reply to message #637591]

Thu, 28 May 2015 12:27

LKBrwn_DBA
Messages: 487
Registered: July 2003
Location: WPB, FL

Senior Member

From the fine Oracle® Database Reference
DB_CACHE_SIZE
Quote:

If SGA_TARGET is set: If the parameter is not specified, then the default is 0 (internally determined by the Oracle Database). If the parameter is specified, then the user-specified value indicates a minimum value for the memory pool.

If SGA_TARGET is not set, then the default is either 48 MB or 4 MB * number of CPUs, whichever is greater

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