Re: How much RAM does Oracle REALLY use?

From: David Trum x4772 <dtrum_at_jetssrg.af.mil>
Date: Tue, 12 May 92 14:00:02 GMT
Message-ID: <1992May12.140002.25876_at_srg.uucp>


Oracle doesn't have to use but just a few Megs. Apparently what is going on, is that the database is tuned up to have a large System Global Area, SGA, in order to cache various accesses and modifications. See the init*.ora file in $ORACLE_HOME/dbs for a list of all current parameters. Also, when the database comes up, it tells you how big the SGA is going to be. One of our instances says 760Kbytes, but partially tuned up, the SGA is over 4Mb. Also, the client connections take up little or no memory when connected and INACTIVE. When issuing selects, et. al., each user process takes up considerably more memory (<=2.5Mb each). This can be limited somewhat by tuning init.ora OR reduced by orders of magnitude for a large number of users by a third party cursor cache product.

Here is the init.ora for one of my instances (actually inittest.ora)

        db_name = test
        db_file_multiblock_read_count = 8

## Change db_block_buffers = 1100 for fast, 220 for slow
db_block_buffers = 220
## Comment next line for fast (default=8)
db_block_write_batch = 5
## Change next two parameters to 250 for fast, 200 for slow
ddl_locks = 200 dml_locks = 200 log_allocation = 14000 log_checkpoint_interval = 10000
## Change processes = 50 for fast, 20 for slow, low load
processes = 20
## Comment out open_cursors for slow (default=50)
## open_cursors=200
##
## Of course the obligitory CONTROL_FILES=3 files on other disks
## and rollback segments = more...
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David E. Trum
Database Administrator		Email:  uunet!srg!dtrum
ARINC Research Corporation	Phone:  (410)266-4772
2551 Riva Road  MS 5-230	Fax:    (410)573-3024
Annapolis, MD  21401-7461
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David E. Trum
Database Administrator		Email:  uunet!srg!dtrum
Received on Tue May 12 1992 - 16:00:02 CEST

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