Title: RE: How Reliable is Explain Plan in 9.2
Thanks Wolfgang ... I understand your point ...
I was just trying to be a little cynical ... about these *facts* ... the very elements about which Oracle tells us to rely upon.
1. Who in their right mind would add/drop an index on a live
I agree with JL. You've never been guaranteed that the plan you generate
after the fact is the same plan that executed at some prior time. If you're
trying to optimize a query using explain plan and are concerned that the
plan may change between when the SQL executed and
when you ran your explain,
MessageIs that something new in 9i? I don't have it in 8.1.7.
- Original Message -
To: Multiple recipients of list ORACLE-L
Sent: Wednesday, March 05, 2003 4:19 PM
A, that is what he is talking about, I wasn't aware of v$sql_plan.
-Original Message-
Sent: Wednesday, March
Yes, the v$sql_plan is new in 9i
-Original Message-
Sent: Thursday, March 06, 2003 10:34 AM
To: Multiple recipients of list ORACLE-L
MessageIs that something new in 9i? I don't have it in 8.1.7.
- Original Message -
To: Multiple recipients of list ORACLE-L
Sent: Wednesday,
Just had a fellow tell me that explain plan in completely unreliable in 9.2
and getting accurate results requires direct SGA access on executing SQL (he
is working in a RAC environment). They are running Precise, a good product,
but this sounds like something a sales person told him. I can only
Title: RE: How Reliable is Explain Plan in 9.2
Ethan,
I am *shocked* we are running RAC 9202 ...
I haven't seen anomalies ... does your friend have any example?
Raj
-
Rajendra dot Jamadagni at espn dot com
Any views expressed
=MS Exchange Server version 5.5.2654.45
TITLERE: How Reliable is Explain Plan in 9.2/TITLE
/HEAD
BODY
PFONT SIZE=2Ethan,/FONT
/P
PFONT SIZE=2I am *shocked* we are running RAC 9202 .../FONT
BRFONT SIZE=2I haven't seen anomalies ... does your friend have any
example?/FONT
/P
PFONT SIZE=2Raj/FONT
Consider how important explain plan is, I highly doubt
it's completely unreliable.
-Original Message-
Sent: Wednesday, March 05, 2003 8:35 AM
To: Multiple recipients of list ORACLE-L
Just had a fellow tell me that explain plan in completely unreliable in 9.2
and getting accurate results
Title: Re: How Reliable is Explain Plan in 9.2
Yes, explain plan will become increasingly unreliable as the cbo takes more
and more factors and current conditions current into account. Some of the
factors that can change the outcome of a parse from session to session are:
for Oracle 8
Title: Re: How Reliable is Explain Plan in 9.2
Wolfgang ...
Now that explain plan is unreliable and will be even more in10i,
I'll always keep a silver dollar in my pocket. The coin toss is still
right(in almost) 50% of the time.
Jeez ... what's next ... in 11i, SELECT statement *may* return
I haven't seen any problems yet.
On the contrary - there are facilities
in the EXPLAIN PLAN which are not
available through v$sql_plan , such
as recursive SQL for subquery
factoring, and a couple of columns
(but I can't remember which ones
at the moment).
Regards
Jonathan Lewis
That is my thinking but I will take Wolfgang's comments into consideration.
-Original Message-
Sent: Wednesday, March 05, 2003 12:39 PM
To: Multiple recipients of list ORACLE-L
Ethan,
Seeing as your friend is running Precise I have heard similar
pronouncements from them about the
I think there's a big emotional difference between
unreliable and won't necessarily give you the plan
under the current circumstances that it gave at the
time of execution - which has been true since the
utility came out. It is true, of course, that the reasons
for the variation have become
Message-From: Jamadagni,
Rajendra [mailto:[EMAIL PROTECTED] Sent: Wednesday,
March 05, 2003 2:30 PMTo: Multiple recipients of list
ORACLE-LSubject: RE: How Reliable is Explain Plan in
9.2
Wolfgang ...
Now that explain plan is unreliable and will be even more in10i,
I'll always
Title: Message
A, that is what he is talking about, I wasn't aware of
v$sql_plan.
-Original Message-From: Toepke, Kevin M
[mailto:[EMAIL PROTECTED]Sent: Wednesday, March 05, 2003 2:30
PMTo: Multiple recipients of list ORACLE-LSubject: RE:
How Reliable is Explain Plan
I have had an interesting case with 8.1.7 recently, working with
autotrace on, and changing optimizer_index_caching and
optimizer_index_cost_adj in my session ... I got the plan I wanted, but
obviously with the response time I didn't want! Apparently, Oracle
noticed the change, but not enough to
Let's not get overboard. It was always the premise in relational databases
that
you tell the database WHAT you want and it is its job and prerogative to
decide HOW
to do it. So the HOW may change at any time, but the results should not. If
they do then it is a bug.
We should also clarify what
17 matches
Mail list logo
