>From the performance tuning guide:
The CBO peeks at the values of user-defined bind variables on the first
invocation of a cursor. This feature lets the optimizer determine the
selectivity of any WHERE clause condition, as well as if literals have been used
instead of bind
variables. On subsequent invocations of the cursor, no peeking takes
place, and the cursor is shared, based on the standard cursor-sharing
criteria, even if subsequent invocations use different bind values.
CBO only peeks the bind variable once, so that wouldn't help much
for star transforms and histograms.
Jared
"Jesse, Rich" <[EMAIL PROTECTED]>
03/10/2003 01:39 PM
To: "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]>
cc: "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]>
Subject: RE: Oracle position on hints
I thought that went out the window with 9i because it can snoop at the
bind
variables??
Rich
Rich Jesse System/Database Administrator
[EMAIL PROTECTED] Quad/Tech International, Sussex, WI USA
-----Original Message-----
Sent: Monday, March 10, 2003 12:09 PM
To: Multiple recipients of list ORACLE-L
Well, I wouldn't say you should *always* use bind variables.
Many situations in a database warehouse preclude that.
Potentially long running queries may need to have literals
to help the CBO make the right choice.
Star transforms don't work with bind variables, and histograms
can't be used with bind variables.
Jared
"Nicoll, Iain" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
03/08/2003 06:23 AM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
cc:
Subject: RE: Oracle position on hints
Given the attitude of most dba's that you should always use bind variables
where possible I can't see how you'd cope with skewed data without them.
Most developers should know a databases's data better than the optimiser
and
certainly when building queries it's always worthwhile seeing where data
is
being most effectively filtered.
There are lots of mature systems out there where the data characteristics
are unlikely to change much and for most in-house developers you're never
going to have to think about portability but always about performance.
Iain Nicoll
-----Original Message-----
Sent: 07 March 2003 16:04
To: Multiple recipients of list ORACLE-L
Hi,
Does Oracle have an official position on hints ?
Will they go away as the optimiser is becoming bettre or they are there to
stay ?
TIA
Stephane Paquette
Administrateur de bases de donnees
Database Administrator
Standard Life
www.standardlife.ca
T�l. (514) 925-7187
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
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