RE: View Mechanics
- From: "Lange, Kevin G" <kevin.lange@xxxxxxxxxx>
- To: <tim@xxxxxxxxx>, "Oracle-L List" <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 2 Sep 2011 12:21:01 -0500
Thanks for the query to list the parms Tim.
We have no undocumented parms set on the database (i.e. no underbar
parms).
The ones you mentioned below were set as follows by default
_pre_rewrite_push_pred TRUE
_push_join_predicate TRUE
_push_join_union_view TRUE
_push_join_union_view2 TRUE
________________________________
From: Tim Gorman [mailto:tim@xxxxxxxxx]
Sent: Friday, September 02, 2011 12:08 PM
To: Lange, Kevin G; Oracle-L List
Subject: Re: View Mechanics
Kevin,
If you can connect to SQL*Plus as SYSDBA (or know someone who can),
perhaps you can run this SQL*Plus script
("http://www.evdbt.com/tools.htm#nondefparm";) that displays all
parameters set to non-default values, including the un-documented ones.
There are several un-documented parameters that can affect whether
predicates get pushed into a view, specifically "_push_join_predicate"
or "_push_join_union_view" or "_pre_rewrite_push_pred" or others.
Hope this helps...
-Tim
-----Original Message-----
From: Lange, Kevin G [mailto:kevin.lange@xxxxxxxxxx]
Sent: Friday, September 2, 2011 10:49 AM
To: 'Oracle-L List'
Subject: RE: View Mechanics
Its repeatable over and over and over on different databases.
Here are the only settings that we use that I imagine would have any
affect on it optimizer_index_caching = 90 optimizer_index_cost_adj = 10
optimizer_mode = CHOOSE query_rewrite_enabled = TRUE -----Original
Message----- From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Powell, Mark Sent:
Friday, September 02, 2011 11:36 AM To: Oracle-L List Subject: RE: View
Mechanics That is strange. Oracle pushing the wehre field = '123' into
the view text and driving off that table would be what I would normally
expect. The resulting query ran in sqlplus should not run better. Do you
have an session level settings changes that need to be taken into
account? Have you made any database parameter setting changes for an of
the parameters that effect the optimizer or set any underbar paramters?
Are any events set in this database? -----Original Message----- From:
oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Lange, Kevin G Sent: Friday, September 02, 2011 11:38 AM To:
Oracle-L List Subject: RE: View Mechanics What we have seen is this: In
the application, running a select from the view in the form of Select *
from app_view where field_a = '123'; Run a lot slower than running the
EXACT code that makes up the view adding the line and field_a = '123' In
the underlying tables field_a is an indexed column. And the columns that
join Table_1 to Table_2 to Table_3 are all indexed. Therefore I would
expect the view to use the same path the sql behind the view when
selecting from it. What we saw when explaining the select from the view
is that all three tables are doing Full Table Scans. When running the
sql outside the view, the appropriate indexes are being used. I just
thought that, all things equal, the view would use the same methods to
get the data that the SQl behind the view did. I had not seen this
drastic a difference before. -----Original Message----- From:
oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Powell, Mark Sent: Friday, September 02, 2011 7:48 AM To:
Oracle-L List Subject: RE: View Mechanics I am not sure I understand
your wording but it is not uncommon to create a view whose SQL query
would be a multiple table join of all rows and if you run select * from
the view the performance would be pretty bad. However, when used in the
application or by the end-user tool a where clause using an indexed
column is provided in the query against the view which in turn when
merged into the view code by the CBO results in a much more selective
plan/performance. -----Original Message----- From:
oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Lange, Kevin G Sent: Thursday, September 01, 2011 6:12 PM To:
Oracle-L List Subject: View Mechanics I am just curious if its common
for an Explain Plan of a view to have a totally different response than
an explain plan of the SQL behind the view. Reason being, we have a very
simple view made of of 3 tables that, when you explain it, it shows full
table scans on all three tables. But, in the mean time, if you explain
plan the SQL behind the view, you get index range scans on all three
tables. Just makes no sense to me (which seems to be happneing more and
more these days). System: Oracle 10.2.0.4 on a Solaris 10 machine. This
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