Message-ID: <3F2FA189.8B5C6F20@rodos.fzk.de>
Date: Tue, 05 Aug 2003 14:22:33 +0200
From: Christoph Haller <ch@rodos.fzk.de>
MIME-Version: 1.0
To: pgsql-sql@postgresql.org, k.p.d.lehre@basalmed.uio.no
Subject: Re: length of recordset read through a cursor
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>
>  >> After declaring a cursor, one way of obtaining the length of the
>  >resultset
>  >> is to perform a "MOVE 0" and read the PQcmdStatus which returns a
>  >"MOVE nn"
>  >> where nn is the length of the resultset. (A negative MOVE can then
be
>  >used
>  >> to allow starting to fetch records from the beginning of the
>  >resultset.)
>  >>
>  >> Is there another, possibly faster way?
>  >>
>  >Looks like you're using libpq (because you mention PQcmdStatus),
>  >then after declaring a cursor and FETCH ALL, try
>  >
>  >1.3.4. Retrieving SELECT Result Information
>  >
>  >    PQntuples Returns the number of tuples (rows) in the query
result.
>  >
>  >    int PQntuples(const PGresult *res);
>  >
>  >I'm not exactly sure what you're trying to achieve or going to do,
>  >so if I misunderstood you, ask again.
>  >
>  >Regards, Christoph
>
> Thanks for your reply.
> What I'm trying to do is the following: I want to browse through a
view
> containing more than 10000 records. To avoid slowing things down too
much,
> I would like my client program to receive (through the network) only
the
> records that are to be displayed on the screen. I believe I could do
this
> by declaring a cursor and then fetching the parts of the resultset I
need.
> It would be useful to know the size of the resultset immediately after
the
> cursor has been declared. How do I get this information? I could of
course
> fetch all of the resultset, but that is what I am trying to avoid.
> Shouldn't it be quicker to perform a move through the set than
fetching it?
> I found that moving zero records results in a move to the end of the
> resultset, with a command status returning the number of records
moved.
> Although I expected this method to take less time than a fetch (does
it?),
> I was wondering if there might be another way to get the size of the
> resultset that can be fetched through the declared cursor.
>
I do not know about the internals of FETCH or MOVE.
To me your first approach looks reasonable. I doubt there is way to
learn
about the size of a resultset simply by declaring a cursor (because
there is
no query taking place yet).
You may like to send your request to the performance list.
Regards, Christoph