Re: Primary Key seems to be harmful for performance
- From: genegurevich@xxxxxxxxxxxxxxxxxxxxx
- To: oracle-l@xxxxxxxxxxxxx
- Date: Thu, 9 Mar 2006 08:12:05 -0600
I was refering to the fact that i had multiple tables in my query and they
all have PKs. I should have been clearer though and say that I have
disabled a PK on one of the tables. I can't modify the SQL in any way
because it is generated by
a reporting tool (Cognos) it won't add hints or +0 etc.
What I was mostly wondering is whether this situation (PK createing a
performance degradation) is a symptom of
some other problem which I need to look at. My first suspect was
statistics, but I ruled that out by analyzing all
tables involved.
thank you
Gene Gurevich
Oracle Engineering
224-405-4079
Nuno Souto
<dbvision@xxxxxxx
et.au> To
Sent by: oracle-l@xxxxxxxxxxxxx
oracle-l-bounce@f cc
reelists.org
Subject
Re: Primary Key seems to be harmful
03/08/2006 06:39 for performance
PM
Please respond to
dbvision@xxxxxxxx
t.au
Quoting genegurevich@xxxxxxxxxxxxxxxxxxxxx:
> in over 2 hours. After looking at the results of the tkprof, I decided to
> disable one of the primary keys. After that the
"one of the primary keys"? That would be of one of the tables?
> same query completed in 10 seconds (!). I have reenabled the PK and query
> ran for much longer (I cancelled it after 10 minues). I have disabled
the
> PK and again the SQL finished in 10 sec.
>
> So it looks like PK is a problem performace-wise. How do I fix it? I
don't
> want to drop that PK; I think that it is needed to make
> sure there is no duplicates and from the DM perspective as well. I was
> wondering whether this is a symptom of some problem with the statistics?
> Does anyone have any suggestions?
Without any specific data on execution plans, all I can reasonably
suggest is that you use a function in the query to disable use of the
pk index by the optimizer. Something like the traditional use of a
nvl() around the leading column(s) of the index, or concatenating a
null to a string or adding 0 (zero) to a number column.
All of them classical ways of making the optimizer ignore a particular
index. You could of course use a hint as well.
That'd be a safer propposition than dropping a PK and losing uniqueness
checks?
--
Cheers
Nuno Souto
from sunny Sydney
--
//www.freelists.org/webpage/oracle-l
--
//www.freelists.org/webpage/oracle-l
Other related posts:
