RE: range-bound queries
- From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxx>
- To: "jonathan@xxxxxxxxxxxxxxxxxx" <jonathan@xxxxxxxxxxxxxxxxxx>, ORACLE-L <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 27 Jul 2009 17:17:36 -0400
Hi Jonathan,
Are wrong results possible? I agree that it's possible that Oracle may not do
what's intended, and that could cause a big performance problem, but I don't
think it will ever return wrong results, will it?
I agree, the solution you point out in the comment is a good idea. I'm just
saying that the way Dan has it written, though poor performance could result, I
don't think a wrong result is possible.
In my case, since the code has been in production for 4+ years, I'm probably
not going to change it, unless we actually run into a problem.....
-Mark
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Jonathan Lewis
Sent: Monday, July 27, 2009 4:49 PM
To: ORACLE-L
Subject: Re: range-bound queries
I think the problem with the code is that it could return the
wrong result as it depends on Oracle using a specific index
in a specific way.
The code towards the end of the response addresses
that issue, though, by including the extra subquery:
"where ip = (select min(ip) > :bind_ip)"
Even if something goes wrong and Oracle uses an
undesirable access path it will still find the correct
value.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
Author: Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
----- Original Message -----
From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxx>
To: <andrew.kerber@xxxxxxxxx>; "ORACLE-L" <oracle-l@xxxxxxxxxxxxx>
Sent: Monday, July 27, 2009 9:42 PM
Subject: RE: range-bound queries
> Hi Andrew,
>
> The article is all Dan Tow. I can’t take credit for any authorship. It all
> started w/ a question I asked here, on Oracle-L, which Dan answered. He got
> the idea for the article, and asked if he could use my name and SQL as is, or
> if I wanted him to obfuscate. I told him to go ahead. But, the authorship
> is
> all him.
>
> As to the rownum=1, the whole idea there is to short circuit the range scan,
> as soon as you have a single match. It’s a way of implementing the idea
> behind the “least-greater-than-or-equal-to” and
> “greatest-less-than-or-equal-to” operators which he discusses in the article.
>
> To answer your questions, the code that Dan provided went into production
> shortly after he provided me that solution, and I believe it’s still going
> strong, 4 years later. Can you expand on your concerns about it being
> “safe”?
> To my knowledge, there’s nothing inherently dangerous about it.
>
> -Mark
>
> From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
> Behalf Of Andrew Kerber
> Sent: Monday, July 27, 2009 4:30 PM
> To: ORACLE-L
> Subject: range-bound queries
>
> I saw an article recently (the article is actually dated 2005), by Dan Tow
> and
> Mark Bobak showing a method of speeding up range bound queries by qualifying
> on rownum=1 as part of the query.
>
> http://linuxdevcenter.com/pub/a/linux/2004/01/06/rangekeyed_1.html
>
> Has anyone been able to successfully do that with production SQL?
>
> If so, are there any special conditions that make this technique safe?
>
> Has anyone found another way to reproduce this effect?
>
>
>
> --
> Andrew W. Kerber
>
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