Re: Cursor behavior

It seems that the task of fetching next n results without moving the cursor seems like too complicated to implement for any query that has
even a little bit of complication in it...

--- On Wed, 12/21/11, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> From: Robert Haas <robertmhaas(at)gmail(dot)com>
> Subject: Re: [HACKERS] Cursor behavior
> To: "amit sehas" <cun23(at)yahoo(dot)com>
> Cc: pgsql-hackers(at)postgresql(dot)org
> Date: Wednesday, December 21, 2011, 8:43 AM
> On Thu, Dec 15, 2011 at 4:15 PM, amit
> sehas <cun23(at)yahoo(dot)com>
> wrote:
> > I had a question about the cursor internals
> implementation. When you Fetch next 'n' results without
> moving the cursors, is this kind of functionality
> implemented by firstly executing the whole query and then
> moving the cursor over the results, or are the movements
> done on active database lookups, moving forward and
> backward...
>
> I think it depends on the query.  For example, I
> believe that a query
> involving writeable CTEs will be run to completion before
> returning
> any results, but I believe that a seqscan will not.
>
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>