RE: Optimizer Mode......how to choose the right one?

From: Christopher Spence <cspence_at_FuelSpot.com>
Date: Tue, 07 Aug 2001 08:49:09 -0700
Message-ID: <F001.00362E54.20010807085552@fatcity.com>

Take a look at index_caching parameters, they can make a big difference when using cost mode, Oracle's settings are very poor.

I have a good article on my site www.vampired.net under Performance which is a great discussion about making the CBO work for you and not against you.

"Do not criticize someone until you walked a mile in their shoes, that way when you criticize them, you are a mile a way and have their shoes."

Christopher R. Spence OCP MCSE MCP A+ RAPTOR CNA Oracle DBA
Phone: (978) 322-5744
Fax: (707) 885-2275

Fuelspot
73 Princeton Street
North, Chelmsford 01863

-----Original Message-----

Sent: Tuesday, August 07, 2001 12:06 PM
To: Multiple recipients of list ORACLE-L

Morning listers!

I am having performance problems with this database, transactions ar running very slow and I am not sure if I have choose the right optimizer mode...

AIX 4.2.1, Oracle 7.3.4, 30 GB Database, 1 GB Real Memory, 500 MB SGA, 70 concurrent users, mostly OLTP transactions.

I have tunned init parameters the best I can we the resources I have:

db_files = 70
db_writers = 4
db_file_multiblock_read_count = 16
db_block_buffers = 57600
db_block_size = 8192

shared_pool_size = 157286400
processes = 200
dml_locks = 1500
log_buffer = 655360

sequence_cache_entries = 800
sequence_cache_hash_buckets = 89
log_checkpoint_interval = 80000

optimizer_mode=CHOOSE
session_cached_cursors = 300

sort_area_size=1048576
hash_area_size=262144
hash_multiblock_io_count=4
hash_join_enabled=TRUE

always_anti_join=HASH
job_queue_processes=8

35 rollback segments, inital 1MB, next 1MB, optimal 30 MB 8 multiplexed redologs, 30 MB each

I tried FIRST_ROWS, analyzing the tables, but users claimed that performance was getting worse, so I chaged it to Choose. Always analyzing the tables....

but, everytime I analyze the tables, performance gets worse. Is this a normal behavior?

Any advice will be welcome!

thanks is advance,

Saludos,
Veronica Levin Enriquez
Administrador AIX
Compañía Cervecera de Nicaragua
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Author: Veronica Levin
INET: vlevin_at_victoria.com.ni

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Author: Christopher Spence
INET: cspence_at_FuelSpot.com

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