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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Optimizer Mode......how to choose the right one?
Does the order of tables also make a
difference with a RULE hint?
Steven HaasOpus Consultants, LLC
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
Sent: Wednesday, August 08, 2001 12:15
PM
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.
<FONT face=Arial color=#0000ff
size=2>
<FONT face=Arial color=#0000ff
size=2>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.
<FONT face=Arial color=#0000ff
size=2>
CNA
is Novell Admin, I haven't done it in a while, I originally started as a
Novell Admin.
<FONT face=Arial color=#0000ff
size=2>Raptor is a firewall product I spent about 4 years working
with.
<FONT face=Arial color=#0000ff
size=2>
"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 <FONT
face="Bell MT" size=1>OCP MCSE MCP A+ RAPTOR CNA <FONT face="Comic Sans MS" size=2>Oracle DBA <FONT face="Comic Sans MS" size=2>Phone: (978) 322-5744 <FONT face="Comic Sans MS" size=2>Fax: (707) 885-2275
face="Comic Sans MS" size=2>73 Princeton Street <FONT
face="Comic Sans MS" size=2>North, Chelmsford 01863 <FONT
face="Comic Sans MS" size=2>
<FONT
face=Tahoma size=2>-----Original Message-----From: Koivu, Lisa
[mailto:lisa.koivu_at_efairfield.com] Sent: Wednesday, August 08,
2001 11:08 AMTo: 'ORACLE-L_at_fatcity.com';
'cspence_at_FuelSpot.com'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 <FONT
face=Arial color=#0000ff size=2>Vikings Fan (and DBA) <FONT
face=Arial color=#0000ff size=2>Ft. Lauderdale, FL, USA
-----Original Message----- <FONT
face=Arial size=1>From: <FONT face=Arial
size=1>Christopher Spence [SMTP:cspence_at_FuelSpot.com] <FONT
face=Arial size=1>Sent: <FONT face=Arial
size=1>Wednesday, August 08, 2001 10:27 AM <FONT face=Arial
size=1>To: <FONT face=Arial
size=1>Multiple recipients of list ORACLE-L <FONT face=Arial
size=1>Subject: <FONT
face=Arial size=1>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 <FONT
face=Arial size=2>Fax: (707) 885-2275
Fuelspot 73
Princeton Street North, Chelmsford
01863
-----Original Message----- <FONT
face=Arial size=2>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 <FONT face=Arial
size=2>>>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 <FONT face=Arial
size=2>have a benefit whether the database selects to use the RBO or
CBO...
IMHO. <FONT face=Arial
size=2>Kev.
__________________
Kevin Thomas <FONT face=Arial
size=2>Technical Analyst Deregulation
Services Calanais Ltd. <FONT
face=Arial size=2>Tel: 0141 568 2314 <FONT face=Arial
size=2>Fax: 0141 568 2366 <A
target=_blank
href="http://www.calanais.com">http://www.calanais.com
-----Original Message----- <FONT
face=Arial size=2>Sent: 07 August 2001 18:36 <FONT face=Arial
size=2>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 <FONT
face=Arial size=2>Fax: (707) 885-2275
Fuelspot 73
Princeton Street North, Chelmsford
01863
-----Original Message----- <FONT
face=Arial size=2>Sent: Tuesday, August 07, 2001 12:37 PM <FONT
face=Arial size=2>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 <FONT
face=Arial size=2>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, <FONT face=Arial
size=2>Kev. (a cheesed off
developer...not a DBA!)
__________________
Kevin Thomas <FONT face=Arial
size=2>Technical Analyst Deregulation
Services Calanais Ltd. <FONT
face=Arial size=2>Tel: 0141 568 2314 <FONT face=Arial
size=2>Fax: 0141 568 2366 <A
target=_blank
href="http://www.calanais.com">http://www.calanais.com
-----Original Message----- <FONT
face=Arial size=2>Sent: 07 August 2001 17:06 <FONT face=Arial
size=2>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 <FONT face=Arial
size=2>db_writers = 4 <FONT face=Arial
size=2>db_file_multiblock_read_count = 16 <FONT face=Arial
size=2>db_block_buffers = 57600 <FONT face=Arial
size=2>db_block_size = 8192 <FONT face=Arial
size=2>shared_pool_size = 157286400 <FONT face=Arial
size=2>processes = 200 dml_locks =
1500 log_buffer = 655360
sequence_cache_entries = 800 <FONT
face=Arial size=2>sequence_cache_hash_buckets = 89 <FONT
face=Arial size=2>log_checkpoint_interval = 80000 <FONT
face=Arial size=2>optimizer_mode=CHOOSE <FONT face=Arial
size=2>session_cached_cursors = 300 <FONT face=Arial
size=2>sort_area_size=1048576 <FONT face=Arial
size=2>hash_area_size=262144 <FONT face=Arial
size=2>hash_multiblock_io_count=4 <FONT face=Arial
size=2>hash_join_enabled=TRUE <FONT face=Arial
size=2>always_anti_join=HASH <FONT face=Arial
size=2>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, <FONT face=Arial
size=2>Veronica Levin Enriquez <FONT face=Arial
size=2>Administrador AIX Compańía
Cervecera de Nicaragua --
Please see the official ORACLE-L FAQ:
<A target=_blank
href="http://www.orafaq.com">http://www.orafaq.com <FONT
face=Arial size=2>-- Author: Veronica
Levin INET:
vlevin_at_victoria.com.ni
Fat City Network Services --
(858) 538-5051 FAX: (858) 538-5051 <FONT face=Arial
size=2>San Diego, California --
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face=Arial size=2>Please see the official ORACLE-L FAQ: <A target=_blank
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Kevin INET:
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Fat City Network Services --
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face=Arial size=2>Please see the official ORACLE-L FAQ: <A target=_blank
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Fat City Network Services --
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face=Arial size=2>-- Author: Thomas,
Kevin INET:
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Fat City Network Services --
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face=Arial size=2>Please see the official ORACLE-L FAQ: <A target=_blank
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Received on Thu Aug 09 2001 - 14:57:57 CDT
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