To: Alessandro Baretta <a.baretta@barettadeit.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs 
In-reply-to: <43CB71AC.20203@barettadeit.com> 
References: <43CB71AC.20203@barettadeit.com>
Comments: In-reply-to Alessandro Baretta <a.baretta@barettadeit.com>
	message dated "Mon, 16 Jan 2006 11:13:00 +0100"
Date: Mon, 16 Jan 2006 12:51:47 -0500
Message-ID: <9766.1137433907@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Alessandro Baretta <a.baretta@barettadeit.com> writes:
> I am aware that what I am dreaming of is already available through
> cursors, but in a web application, cursors are bad boys, and should be
> avoided. What I would like to be able to do is to plan a query and run
> the plan to retreive a limited number of rows as well as the
> executor's state. This way, the burden of maintaining the cursor "on
> hold", between activations of the web resource which uses it, is
> transferred from the DBMS to the web application server,

This is a pipe dream, I'm afraid, as the state of a cursor does not
consist exclusively of bits that can be sent somewhere else and then
retrieved.  There are also locks to worry about, as well as the open
transaction itself, and these must stay alive inside the DBMS because
they affect the behavior of other transactions.  As an example, once
the cursor's originating transaction closes, there is nothing to stop
other transactions from modifying or removing rows it would have read.

			regards, tom lane