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

On Thu, Jan 21, 2021 at 1:30 PM Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>
wrote:

> Hello.
>
> At Wed, 18 Nov 2020 15:05:00 +0300, a(dot)pervushina(at)postgrespro(dot)ru wrote in
> > 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.
>
> According to the discuttion here, implementing as functions is not
> optimal. As a Poc, I made it as a procedure. However I'm not sure it
> is the correct implement as a native procedure but it seems working as
> expected.
>
> > Usage examples
> > ==========
> > select pg_waitlsn(‘LSN’, timeout);
> > select pg_waitlsn_infinite(‘LSN’);
> > select pg_waitlsn_no_wait(‘LSN’);
>
> The first and second usage is coverd by a single procedure. The last
> function is equivalent to pg_last_wal_replay_lsn(). As the result, the
> following procedure is provided in the attached.
>
> pg_waitlsn(wait_lsn pg_lsn, timeout integer DEFAULT -1)
>
> Any opinions mainly compared to implementation as a command?
>
> regards.
>
> --
> Kyotaro Horiguchi
> NTT Open Source Software Center
>

The patch (pg_waitlsn_v10_2_kh.patch) does not compile successfully and has
compilation errors. Can you please take a look?

https://cirrus-ci.com/task/6241565996744704

xlog.c:45:10: fatal error: commands/wait.h: No such file or directory
#include "commands/wait.h"
^~~~~~~~~~~~~~~~~
compilation terminated.
make[4]: *** [<builtin>: xlog.o] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [../../../src/backend/common.mk:39: transam-recursive] Error 2
make[2]: *** [common.mk:39: access-recursive] Error 2
make[1]: *** [Makefile:42: all-backend-recurse] Error 2
make: *** [GNUmakefile:11: all-src-recurse] Error 2

I am changing the status to "Waiting on Author"

--
Ibrar Ahmed