Re: modelling physical writes

  • From: Stephane Faroult <sfaroult@xxxxxxxxxxxx>
  • To: ryan_gaffuri@xxxxxxxxxxx
  • Date: Wed, 13 Sep 2006 21:53:36 +0200


You cannot relate writes to one particular SQL statement since they are performed on a system-wide basis by dbwr and friends. Ditto with redo. I think that the best you can do it to take a snapshot of v$sesstat before and after your statement/package for the most relevant statistics. And even so, I fear that for regular block-writes it would not be very useful. Assume that you have several concurrent sessions concurrently updating the same data block. How will you render unto Caesar the things that are Caesar's?


Stéphane Faroult

ryan_gaffuri@xxxxxxxxxxx wrote:
How do we get solid numbers to determine how many physical writes a specific sql or pl/sql package will perform? When we use 10046 I believe it only gets physical reads because the dbwriter is asynchronous? I have some concerns about using AWR for this. Also, how do we get reliable redo numbers? When I use set autotrace on and run the same insert multiple times the redo seems to vary by 20% or so.

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