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Keep Buffer Pool [message #637572] Wed, 20 May 2015 06:14 Go to next message
fabi88
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Registered: November 2011
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?


Re: Keep Buffer Pool [message #637573 is a reply to message #637572] Wed, 20 May 2015 06:21 Go to previous messageGo to next message
John Watson
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Registered: January 2010
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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.
Re: Keep Buffer Pool [message #637575 is a reply to message #637573] Wed, 20 May 2015 06:22 Go to previous messageGo to next message
gazzag
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Quote:
Uncle Oracle
Very Happy
Re: Keep Buffer Pool [message #637578 is a reply to message #637572] Wed, 20 May 2015 06:31 Go to previous messageGo to next message
fabi88
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Registered: November 2011
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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?

Re: Keep Buffer Pool [message #637580 is a reply to message #637578] Wed, 20 May 2015 06:48 Go to previous messageGo to next message
John Watson
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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 Go to previous messageGo to next message
fabi88
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Registered: November 2011
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Thank you.
Re: Keep Buffer Pool [message #637591 is a reply to message #637578] Wed, 20 May 2015 09:30 Go to previous messageGo to next message
bpeasland
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Registered: February 2015
Location: United States
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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
Re: Keep Buffer Pool [message #637600 is a reply to message #637591] Wed, 20 May 2015 10:36 Go to previous messageGo to next message
Michel Cadot
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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

icon12.gif  Re: Keep Buffer Pool [message #637902 is a reply to message #637591] Thu, 28 May 2015 12:27 Go to previous message
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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