tables in the FROM clause RIGHT to LEFT. CBO determines join order from costs derived from gathered statistics. If there are no stats then CBO chooses the driving order of tables from LEFT to RIGHT in the FROM clause. This is OPPOSITE to the RBO.
"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-----
From: Vadim Gorbounov [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, August 08, 2001 12:09 PM
To: '[EMAIL PROTECTED]'
Subject: RE: Optimizer Mode......how to choose the right one?Chris,Sorry for taking your time, but it seems ORDERED matters with CBO. What about Note:35934.1,they say quite opposite to yours:Hints
- Any hint, except RULE, causes CBO to be used.
It is very important to note that a HINT cannot be 'turned
off' by any parameter settings.Any thoughts? Did I get something wrong? I think, Ordered will essentially reduce # of permutation optimizer makes to calculate cheapest access path.Vadim Gorbounov,Oracle DBA-----Original Message-----
From: Christopher Spence [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, August 08, 2001 12:16 PM
To: Multiple recipients of list ORACLE-L
Subject: RE: Optimizer Mode......how to choose the right one?I by no means say CBO doesn't make mistakes. It by far does, but the original statement stays accurate, order of tables only matters with RBO (if comes up with tie) and ordered hint.There is nothing wrong with getting it in a good order, I just wanted to stress that it only truely matters during those two conditions. That's all, not trying to be adversary.CNA is Novell Admin, I haven't done it in a while, I originally started as a Novell Admin.Raptor is a firewall product I spent about 4 years working with."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) 885-2275Fuelspot
73 Princeton Street
North, Chelmsford 01863
-----Original Message-----
From: Koivu, Lisa [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, August 08, 2001 11:08 AM
To: '[EMAIL PROTECTED]'; '[EMAIL PROTECTED]'
Subject: RE: Optimizer Mode......how to choose the right one?Ahh, but Christopher, therein lies the problem. The CBO makes mistakes and sometimes needs the gentle nudging of the ORDERED hint. I've seen a query go from hours to 2 seconds after some analysis of the execution plan that was failing miserably.
Love the sig. You are a CNA? A Raptor? Am I missing something?
Lisa Koivu
Vikings Fan (and DBA)
Ft. Lauderdale, FL, USA
-----Original Message-----
From: Christopher Spence [SMTP:[EMAIL PROTECTED]]
Sent: Wednesday, August 08, 2001 10:27 AM
To: Multiple recipients of list ORACLE-L
Subject: RE: Optimizer Mode......how to choose the right one?The driving table order does not matter when using CBO, it will detirmine
the order based on cost, not placement.The order only matters when dealing with the RBO (when it hits a tie,
otherwise it will change it, but this happens often), or when using the
ordered hint."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) 885-2275Fuelspot
73 Princeton Street
North, Chelmsford 01863
-----Original Message-----
Sent: Wednesday, August 08, 2001 4:30 AM
To: Multiple recipients of list ORACLE-L
>>Order of the tables only matters when using the ORDERED hint or using
>>rbo AND there is a tie ranking.But surely the very nature of the CHOOSE hint is to select the best method
to use whether it's to follow the RBO or the CBO. Therefor ensuring that you
have the driving table defined in the correct place within the query will
have a benefit whether the database selects to use the RBO or CBO...IMHO.
Kev.
__________________
Kevin Thomas
Technical Analyst
Deregulation Services
Calanais Ltd.
Tel: 0141 568 2314
Fax: 0141 568 2366
http://www.calanais.com
-----Original Message-----
Sent: 07 August 2001 18:36
To: Multiple recipients of list ORACLE-L
When using first rows, you force the cost based optimizer, in which the
order of the tables does not matter.Order of the tables only matters when using the ORDERED hint or using rbo
AND there is a tie ranking."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) 885-2275Fuelspot
73 Princeton Street
North, Chelmsford 01863
-----Original Message-----
Sent: Tuesday, August 07, 2001 12:37 PM
To: Multiple recipients of list ORACLE-L
Hi there,
Unfortunately you can't just throw things like FIRST_ROWS at a select
statement to make it run faster. The person who wrote the statement should
have taken into account such things as:a) Size of tables, ordering, which is the driving table
b) Indexes, are the being used, running statements through explain plan will
show you where the bottlenecks are...failing that TKPROF will identify
potential problem areas with your database.
c) Size of queries, joins etc.Too many developers do not write code to be efficient, as long as it returns
the correct values it doesn't matter whether it takes 2 minutes or 2
hours...I've spent a number of hours/days/weeks/months tidying up poorly optimised
code, it's an absolute nightmare for the DBAs and it doesn't look good on
the developers.Cheers,
Kev.
(a cheesed off developer...not a DBA!)
__________________
Kevin Thomas
Technical Analyst
Deregulation Services
Calanais Ltd.
Tel: 0141 568 2314
Fax: 0141 568 2366
http://www.calanais.com
-----Original Message-----
Sent: 07 August 2001 17:06
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=835 rollback segments, inital 1MB, next 1MB, optimal 30 MB
8 multiplexed redologs, 30 MB eachI 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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