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Hello,
SQL> select * from v$sga;
NAME VALUE
-------------------- ---------
Fixed Size 65484
Variable Size 19521536
Database Buffers 16777216
Redo Buffers 73728
In above queries database buffer size comes from db_block_buffers = 8192 # INITIAL parameter of init.ora file. But other parameters like fixed size ,var. size , redo buffers are coming from where ?
How to calculate the memory occupied by an instance ?
Sunil
To approximate size of the SGA (Shared Global Area), use the following formula:Quote:
Sample from svrmgrl SHOW SGA:
Total System Global Area 23460696 bytes
Fixed Size 72536 bytes
Variable Size 22900736 bytes
Database Buffers 409600 bytes
Redo Buffers 77824 bytes
Total System Global Area
- Total in bytes of all the sub-divisions that makes up the SGA.
Fixed Size
- Contains general information about the state of the database and the instance, which the background processes need to access.
- No user data is stored here.
- This area is usually less than 100k in size.
Variable Size
- This section is influenced by the following init.ora parameters
shared_pool_size
large_pool_size
java_pool_size
- See 'Approximating Size of the SGA' section of this article for version specific information.
Database Buffers
- Holds copies of data blocks read from datafiles.
size = db_block_buffers * block size
Redo Buffers
- A circular buffer in the SGA that holds information about changes made to the database.
- Enforced mininum is set to 4 times the maximum database block size for the host operating system.
((db_block_buffers * block size) +
(shared_pool_size + large_pool_size + java_pool_size + log_buffers) + 1MB
Sam
[Edited by sambavan on 10-30-2001 at 04:33 PM]
To Sam's good output, I would like to add that in case you use a multi-instanced DB, you have to add (in the formula above) the Instance Lock Database.Quote:
To approximate size of the SGA (Shared Global Area), use the following formula:
((db_block_buffers * block size) +
(shared_pool_size + large_pool_size + java_pool_size + log_buffers) + 1MB
You can calculate your locks by changing the init.ora parameter GC_FILES_TO_LOCKS and counting the difference. Results are platform dependent but I would say that 64 bytes for a PCM lock is a good estimate.