Re: RE: full usefullness of CURRENT OF ???

when you update inside of a cursor you have two steps.

Fetch data into the cursor
Update the table based on what you selected.

So while you are selecting data and before you update, the record could change. This means someone else could update it and youc ould update over it without knowing it. This is a bad idea in the database world and is known as 'disapearing updates'. So you lock the row when you select it. Not when the actual update is processed.

Updating inside of cursors is generally a bad idea. Its more code and its MUCH slower than a straight update statement. Ive seen some publications stating that it can before to do this way, but Ive tested every case I can think of and not once was it even close.

what is the update statement you want to put inside the cursor?
>
> From: MaryAnn Atkinson <maryann_30_at_yahoo.com>
> Date: 2003/07/11 Fri PM 04:09:25 EDT
> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> Subject: RE: full usefullness of CURRENT OF ???
>
> --- Chris Stephens <ChrisStephens_at_affina.com> wrote:
> > Also, the CURRENT OF locks the table so that no one can modify (or
> > even read) it while the transaction is taking place. This guarantees
> > nothing is changing between retrieving values from the cursor and
> > updating the table based on those values.
>
> OK, fair enough.
>
>
> > The second example has to run the update statement seperately.
> > CURRENT OF can go directly to the row(s) affected. CURRENT OF
> > still has to modify each block header in the table to lock which
> > is a small performance hit.
>
> So CURRENT OF has to lock, so its slower, right?
> Does it have any advantages after all?
>
> >To prevent that you could update by rowid
> How? How can I update by ROWID? I was thinking to update
> by PRIMARY_KEY...
>
> > and avoid the header updates.
>
> ... what "header" updates?
>
> thx
> maa
>
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