"Somu" <soumya_ongc_at_yahoo.com> wrote in message
news:9666da71.0404022207.210635d8_at_posting.google.com...
> "Michel Cadot" <micadot{at}altern{dot}org> wrote in message
news:<406d69b9$0$12801$626a14ce_at_news.free.fr>...
> > "Somu" <soumya_ongc_at_yahoo.com> a écrit dans le message de
> > news:9666da71.0404020103.7e174d21_at_posting.google.com...
> > > Hi,
> > > I have some doubts on the above mentioned topic.
> > >
> > > As I understand, Oracle use Data buffer cache to store the data frm
> > > data file in memory for efficient transaction. Consider a case, when a
> > > row of a table is modified by a user,that means earlier row values are
> > > in roll back segment,current changed value in data buffer cache and
> > > info regarding this transaction in redo log buffer.Now suppose the
> > > user has committed the transaction.So redo log buffer content gets
> > > copied to redo log file.But as DBW writes to the data files at some
> > > time interval(viz 3 sec) and commit itself doesnot invoke any
> > > checkpoint so its clear that at this instance data files are not
> > > updated.Now suppose the user issues Select query to see that
> > > particular row fields ,now as par with data consistency Oracle will
> > > show the comitted data.
> > > Now my question comes into picture.Where from Oracle
> > > show this updated data? Apparently it seems from Data Buffer cache.So
> > > does this cache has information that explicitly says following info
> > > a)this block is changed but not comitted
> > > b)this block is changed and comitted but not written back
> > > to data files
> > > c)this block is changed and comitted and written back to
> > > data files
> > >
> > > Waiting for some positive response.
> > > Thanks and Regards
> > > somu
> >
> > Have a look at Metalink note 40689 "ORA-01555 "Snapshot too old" -
Detailed Explanation", url:
> >
http://metalink.oracle.com/metalink/plsql/ml2_documents.showDocument?p_database_id=NOT&p_id=40689.1
> >
> > There is a detailed description of how "commited" flag is propagated.
> >
> > Regards
> > Michel Cadot
>
>
>
> Michel
>
> Thanks for your reponse.But unfortunately I cant open your link.I dont
> have the required access to this metalink site.
> Rgds
> Somu
Then you need to get the Metalink account information from the person in
your organization who has access to Oracle Support.(answer is rollback or
undo)
Jim
Received on Sat Apr 03 2004 - 07:31:09 CST
