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Reg Buffers [message #218710] Fri, 09 February 2007 07:50 Go to next message
Messages: 240
Registered: June 2005
Location: India
Senior Member

Firstly i queried the dynamic view

select * from v$sga

I could find the name like database buffer and redo buffers with the values 245760000 & 319488.

Then i checked the v$parameter view, i found the entries like following
db_block_buffer = 15000

what is the difference in these?
why values are different?

Re: Reg Buffers [message #218728 is a reply to message #218710] Fri, 09 February 2007 10:13 Go to previous message
Mahesh Rajendran
Messages: 10677
Registered: March 2002
Location: oracleDocoVille
Senior Member
Account Moderator
Always post your version and some proof of what you did.
Literally describing what you did, helps very little.
Depending on your version, Check v$sgainfo.
From 10g, the values passed on through init.ora parameters are accurately displayed. For example, let take 
the output of SHOW SGA. Here Fixed SGA is platform dependent and is almost a constant. Variable SGA 
is sum of shared_pool_size + large_pool_size + java_pool_size Etc. Database buffers is value of 
(db_block_buffers * block size). Redo Buffers is values of LOG_BUFFER. The sum of Fixed Size + 
Variable Size + Database Buffers + Redo buffers is the Total SGA allocated. 
SQL> show sga 
Total System Global Area  293601280 bytes 
Fixed Size                  1978176 bytes 
Variable Size              96473280 bytes 
Database Buffers          192937984 bytes 
Redo Buffers                2211840 bytes 
-- Let us cross check these numbers individually. 
SQL> select '293601280'/(1024*1024) as sga_in_megs_from_SHOW_SGA from dual; 
SQL> get compute_sga 
  1  compute sum of Size_in_megs on report; 
  2  break on report; 
  3  select name , round(bytes/(1024*1024)) "Size_in_megs" from v$sgainfo 
  4  where name in ('Fixed SGA Size','Shared Pool Size','Large Pool Size', 
  5* 'Java Pool Size','Redo Buffers','Buffer Cache Size') 
SQL> @compute_sga 
NAME                             Size_in_megs 
-------------------------------- ------------ 
Fixed SGA Size                              2 
Redo Buffers                                2 
Buffer Cache Size                         184 
Shared Pool Size                           84 
Large Pool Size                             4 
Java Pool Size                              4 
sum                                       280 
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