От: Tom Lane
Тема: Re: Suspending SELECTs
Дата: ,
Msg-id: 9766.1137433907@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Suspending SELECTs  (Alessandro Baretta)
Ответы: Re: Suspending SELECTs  (Alvaro Herrera <-ip.org>)
Re: Suspending SELECTs  ("Craig A. James")
Re: Suspending SELECTs  (Alessandro Baretta)
Список: pgsql-performance

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Suspending SELECTs  (Alessandro Baretta, )
 Re: Suspending SELECTs  (Tom Lane, )
  Re: Suspending SELECTs  (Alvaro Herrera <-ip.org>, )
   Re: Suspending SELECTs  (Tom Lane, )
  Re: Suspending SELECTs  ("Craig A. James", )
   Re: Suspending SELECTs  (Alessandro Baretta, )
    Re: Suspending SELECTs  ("Jim C. Nasby", )
    Re: Suspending SELECTs  (Mark Lewis, )
    Re: Suspending SELECTs  ("Craig A. James", )
  Re: Suspending SELECTs  (Alessandro Baretta, )
   Re: Suspending SELECTs  (Michael Stone, )
   Re: Suspending SELECTs  (Tom Lane, )
   Re: Suspending SELECTs  (, )
    Re: Suspending SELECTs  (Frank Wiles, )
    Re: Suspending SELECTs  (Mark Kirkwood, )
     Re: Suspending SELECTs  (Tom Lane, )
      Re: Suspending SELECTs  (Mark Kirkwood, )
    Re: Suspending SELECTs  (Alessandro Baretta, )
     Re: Suspending SELECTs  (Tino Wildenhain, )
     Re: Suspending SELECTs  (, )
      Re: Suspending SELECTs  (Alessandro Baretta, )
       Re: Suspending SELECTs  (Harry Jackson, )
        Re: Suspending SELECTs  (, )
   Re: Suspending SELECTs  (Josh Berkus, )
    Re: Suspending SELECTs  (Josh Berkus, )
     Re: Suspending SELECTs  (Alessandro Baretta, )
      Re: Suspending SELECTs  (August Zajonc, )
       Re: Suspending SELECTs  (Alessandro Baretta, )
 Re: Suspending SELECTs  (Mark Lewis, )

Alessandro Baretta <> 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


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