RE: db file scattered/sequential read wait

We are running SAP and there is a hourly background job which
runs SQL against dba_segmen and dba_extents. I believe the 
program name is SAPLSDO0. Anyway, my question is: why it never
bring down our databases?

-----Original Message-----
From: Wolfgang Breitling [mailto:breitliw@xxxxxxxxxxxxx]
Sent: Wednesday, June 16, 2004 1:21 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: db file scattered/sequential read wait


Just a word of caution. You don't want to run this query every time you want to 
find out the object for a db file read. That alone could bring your system to 
its knees, especially if you have LMTs - and if not, why not? (those who still 
manage Oracle 7 and lower systems are excused).
I run something like that in the wee hours of the morning when there is spare 
capacity and load the response into a table indexed by file# and block#. This 
way I don't go after the catalog tables and the response is immediate. Sure, I 
risk missing the occasional block (hasn't happened yet) if the object went into 
a new extent after I ran my report. 

Quoting "Mark W. Farnham" <mwf@xxxxxxxx>:

> I think you want a minus one in the second term.
> 
> Let's see, if block_id = 1 and you read 8 blocks, then 1...9, is *not* what
> you want, so yeah, (block_id+blocks-1)
> would tighten up that predicate.
> 
> mwf
> 

-- 
regards

Wolfgang Breitling, 
Oracle 7,8,8i,9i OCP DBA; Oaktable member
Centrex Consulting Corporation
www.centrexcc.com

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