Thread: Re: [HACKERS] make async slave to wait for lsn to be replayed

Hello,

I've changed the BEGIN WAIT FOR LSN statement to core functions 
pg_waitlsn, pg_waitlsn_infinite and pg_waitlsn_no_wait.
Currently the functions work inside repeatable read transactions, but 
waitlsn creates a snapshot if called first in a transaction block, which 
can possibly lead the transaction to working incorrectly, so the 
function gives a warning.

Usage examples
==========
select pg_waitlsn(‘LSN’, timeout);
select pg_waitlsn_infinite(‘LSN’);
select pg_waitlsn_no_wait(‘LSN’);

Hi!

On Mon, Nov 16, 2020 at 1:09 PM <a.pervushina@postgrespro.ru> wrote:
> I've changed the BEGIN WAIT FOR LSN statement to core functions
> pg_waitlsn, pg_waitlsn_infinite and pg_waitlsn_no_wait.
> Currently the functions work inside repeatable read transactions, but
> waitlsn creates a snapshot if called first in a transaction block, which
> can possibly lead the transaction to working incorrectly, so the
> function gives a warning.
>
> Usage examples
> ==========
> select pg_waitlsn(‘LSN’, timeout);
> select pg_waitlsn_infinite(‘LSN’);
> select pg_waitlsn_no_wait(‘LSN’);

The name pg_waitlsn_no_wait() looks confusing.  I've tried to see how
it's documented, but the patch doesn't contain documentation...

------
Regards,
Alexander Korotkov