Re: ctid & updates

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От Jan Wieck
Тема Re: ctid & updates
Дата
Msg-id 200206041416.g54EGAH04751@saturn.janwieck.net
обсуждение исходный текст
Ответ на Re: ctid & updates  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: ctid & updates  (Tom Lane <tgl@sss.pgh.pa.us>)
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Tom Lane wrote:
> "Joshua b. Jore" <josh@greentechnologist.org> writes:
> > I noticed that ctid changes on update (as expected since it's really a new
> > row). Is there anyway to get the new ctid from the update so later
> > updates to the row can continue to use ctid to zero in on the row
> > location?
>
> There's a function called something like currtid that takes the
> CTID of the possibly-obsoleted row and returns the CTID of its latest
> updated version.  I believe this is exported because the ODBC driver
> uses it, so it's unlikely to go away, even though AFAIR it's not
> documented anywhere.  A risk of using it is that CTID of an updated
> row cannot be trusted for very long --- once VACUUM has come by,
> you might find that CTID reassigned to some other row entirely.

    But  it  should  be  safe within the transaction that did the
    update,  right?   And  since  cursors  (in  PG)  cannot  span
    multiple  transactions,  this  would  be  the  last piece I'm
    looking for to use in UPDATE ... WHERE CURRENT OF.

    Thanks.


Jan

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