Re: primary keys and dictionary overhead

>> As far as UK constraints. We use unique indexes. We don't define them as
>> constraints. Functionally its the same thing, but they don't show up in the
>> DBA_CONSTRAINTS views. I am not sure how much of a difference that makes in
>> data dictionary activity. I have not checked yet.

The definition of a constraint *IS* a big deal. A constraint (to quite Ton 
Kyte) is a semantic thing, it tells people (and the database) things. To quote 
Tom on this topic, he says 
the following :

if you have a unique constraint, a data integrity constraint that says "thou 
are unique" - it only 
makes sense to use.....

a UNIQUE CONSTRAINT


a unique index is NOT a unique constraint, it is a unique index.  the optimizer 
will use 
constraints as well as available indexes and so on when deciding on what to do.

Assert all constraints - if we choose to use a unique index to enforce it, 
great - but don't create 
a unique index and tell me you have a constraint, you don't.  You missed out. 
From: 
http://asktom.oracle.com/pls/asktom/f?p0:11:0::::P11_QUESTION_ID:8743855576462

 
Robert G. Freeman
Master Principal Consultant, Oracle Corporation, Oracle ACE
Author of various books on RMAN, New Features and this shorter signature line.
Blog: http://robertgfreeman.blogspot.com


Note: THIS EMAIL IS NOT AN OFFICIAL ORACLE SUPPORT COMMUNICATION. It is just 
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________________________________
From: Dba DBA <oracledbaquestions@xxxxxxxxx>
To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, October 21, 2011 9:12 AM
Subject: Re: primary keys and dictionary overhead

Thank you for the responses. I have been busy and unable to catch up the
last few days. First off I know to test it myself. I know I can run a
tkprof. However, I don't think that is sufficient. I can't recreate the
volumes that we get in production. So I was looking for a little more
information to see if anyone has seen anything. There is a limit to the
level of volume tests I can run. Has anyone written a paper or a
presentation on this?
As far as UK constraints. We use unique indexes. We don't define them as
constraints. Functionally its the same thing, but they don't show up in the
DBA_CONSTRAINTS views. I am not sure how much of a difference that makes in
data dictionary activity. I have not checked yet.

As far as the email about a few vendors who insisted doing this and then
didn't use bind variables. We use bind variables. James Morle was one of the
guys who worked on this database. One of the guys who is still here worked
with him and they both decided to pull the constraints and everything out.
No synonyms. Only grants to public. I think he wrote about some of his
experiences on another application back then in the Tales From the Oak Table
book. It might be his own book from the late 1990s. I can't remember. I was
still in college when they first built this database and had never even
heard of Oracle.


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