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Re: v$transaction.cr_gets

From: Charles Hooper <>
Date: Thu, 05 Jul 2007 13:29:20 -0700
Message-ID: <>

On Jul 5, 2:38 pm, Chuck <> wrote:
> DA Morgan wrote:
> > Chuck wrote:
> >> DA Morgan wrote:
> >>> Chuck wrote:
> >>>> wrote:
> >>>>> On Fri, 29 Jun 2007 18:05:07 GMT, Chuck
> >>>>> <> wrote:
> >>>>>> What exactly does this column represent? The docs simply say
> >>>>>> 'Consistent
> >>>>>> gets'. Is it all consistent gets for the transaction? Or is it
> >>>>>> just gets
> >>>>>> that required rolling back a change from the undo segment listed
> >>>>>> in the
> >>>>>> xidusn column?
> >>>>> Please read up on what consistent gets are.
> >>>> Please reread the question. Your smug answers are not helpful.
> >>> Before you jump on Sybrand you might want to spend the 10-15
> >>> seconds required to look up the definition of "consistent gets"
> >>> in the Oracle docs. It really is self-explanatory and there
> >>> really is nothing smug or unhelpful about Sybrand's response.
> >>> It is not his, or anyone else's, responsibility to do your
> >>> tahiti search for you. You were pointed to the correct answer
> >>> and it couldn't be more straight-forward unless English is not
> >>> a language with which you are comfortable.
> >> I already know what consistent gets are. They are blocks read in
> >> consistent mode - which means they may or may not have required
> >> reading an undo block to construct a read-consistent view of the data.
> >> So once again back to my question - Are the consistent gets referenced
> >> in v$transaction all consistent gets for the transaction, or are they
> >> just the ones needed to be rolled back from the undo segment also
> >> referenced on the same row of v$transaction. The Oracle documentation
> >> on this column - which I did read - is extremely lacking.
> > Not trying to be obtuse here but everyone is pointing you that direction
> > and it is for a good reason. I'm not treating you any differently than I
> > would treat one of my students that asked the question.
> > Go to
> > Put in your search criterion: "v$transaction"
> > and you find 6 links. Read them all and if you still don't understand
> > what you've written then post the specific sentences and links and help
> > us understand what you don't get.
> They were already posted. In fact it was a direct quote from that exact
> search you're suggesing I run.
> If you don't want to answer the question then don't but please stop
> trolling. In the mean time I'll take the question somewhere else where
> folks understand how a consistent get is done (i.e. that it can involve
> undo segments) and post the answer here for anyone else who may have the
> same question and stumble on this thread.

If you are interested in determining when undo is involved, maybe you should be looking at CONSISTENT CHANGES, the CR_CHANGE column in V $TRANSACTION:

Statistic descriptions: "consistent changes: Number of times a user process has applied rollback entries to perform a consistent read on the block. Work loads that produce a great deal of consistent changes can consume a great deal of resources. The value of this statistic should be small in relation to the 'consistent gets' statistic"

Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc. Received on Thu Jul 05 2007 - 15:29:20 CDT

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