public inbox for [email protected]  

help / color / mirror / Atom feed

From: Andy Fan <[email protected]>
To: Robert Haas <[email protected]>
Cc: Etsuro Fujita <[email protected]>
Cc: Pg Hackers <[email protected]>
Subject: Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior
Date: Fri, 06 Dec 2024 18:50:25 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+TgmoaYs6DLXrZB8NWzUi3YPL9yvBhFOG4UMENMCJ+WY2pn5A@mail.gmail.com>
References: <CAPmGK14Nj7vuJELKuhyiwMMhat8SsyUY+88yAyTZLdqXG0xYuw@mail.gmail.com>
	<CA+TgmoaYs6DLXrZB8NWzUi3YPL9yvBhFOG4UMENMCJ+WY2pn5A@mail.gmail.com>

Robert Haas <[email protected]> writes:

> On Thu, Dec 5, 2024 at 4:41 AM Etsuro Fujita <[email protected]> wrote:
>> Comments welcome!  Maybe I am missing something, though.
>
> I have a hard time seeing how this would work if cursors are in use on
> the main server. Say I do this:
>
> DECLARE foo CURSOR FOR SELECT * FROM ft1 UNION ALL SELECT * FROM ft2;
> ...fetch some rows from cursor foo but few enough that we only scan ft1...
> ...do something that causes a snapshot refresh like issue another query...
> ...fetch more rows from cursor foo until we start scanning ft2...

Apart from the above issue, what do you think about that we are using a
'SELECT pg_catalog.pg_refresh_snapshot()' to let the remote do the
refresh_snapshot VS 'a new message type for this'?  There are lots of
things happen in the 'SELECT' way like 'a extra network communication',
'a complete parser-planner-executor workflow.' With a new message type
for this, we can send the message character with the next query
together. if so, can the two overheads removed? 


-- 
Best Regards
Andy Fan

view thread (4+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox