Re: db file scattered/sequential read wait

  • From: Daniel Fink <Daniel.Fink@xxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Wed, 16 Jun 2004 12:34:11 -0600

Wolfgang,

Excellent word of caution. I use a global temp table that I load up with the output from dba_segments, slap an index on it and perform the query. The whole process takes a fraction of what it takes to apply this type of predicate to the dba_segments query.

Regards,
Daniel Fink



Wolfgang Breitling wrote:
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




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