Re: Incorrect description of xmax and xip in functions docs

Simon Riggs wrote:
>
> On Wed, 2009-01-07 at 20:30 -0500, Bruce Momjian wrote:
>
> > > The only way is to document it.
> >
> > Sorry, I am just getting back to this. Why would we not know if
> > something is a subtransaction or if subtransactions are supported? Are
> > you assuming txid_visible_in_snapshot() will be used on different
> > servers? What are these txid_* functions for anyway?
>
> You can derive a snapshot and export it using txid_current_snapshot().
> http://developer.postgresql.org/pgdocs/postgres/functions-info.html
>
> You can then check whether an xid is in that snapshot by running
> txid_visible_in_snapshot(). However, the check is done assuming that the
> xid you are checking is a top-level xid and the answer you get is either
> yes or no.
>
> There is no allowance made that the xid supplied as a parameter value
> may have been a subtrans of one of the top-level xids listed. So the
> answer *ought* to have been true, whereas the function will always
> return false.
>
> We cannot extend txid_visible_in_snapshot() to answer correctly because
> that information is not held within the snapshot datatype, nor is it
> held in regular snapshots currently. So the only way to handle this is
> to document the limited scope of the answer this function provides.

Thank you for the clarification; I know understand. Patch attached and
applied.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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