Re: Implement waiting for wal lsn replay: reloaded

In 0002 you have this kind of thing:

> ereport(ERROR,
> errcode(ERRCODE_QUERY_CANCELED),
> - errmsg("timed out while waiting for target LSN %X/%08X to be replayed; current replay LSN %X/%08X",
> + errmsg("timed out while waiting for target LSN %X/%08X to be %s; current %s LSN %X/%08X",
> LSN_FORMAT_ARGS(lsn),
> - LSN_FORMAT_ARGS(GetXLogReplayRecPtr(NULL))));
> + desc->verb,
> + desc->noun,
> + LSN_FORMAT_ARGS(currentLSN)));
> + }

I'm afraid this technique doesn't work, for translatability reasons.
Your whole design of having a struct with ->verb and ->noun is not
workable (which is a pity, but you can't really fight this.) You need to
spell out the whole messages for each case, something like

if (lsntype == replay)
ereport(ERROR,
errcode(ERRCODE_QUERY_CANCELED),
errmsg("timed out while waiting for target LSN %X/%08X to be replayed; current standby_replay LSN %X/%08X",
else if (lsntype == flush)
ereport( ... )

and so on. This means four separate messages for translation for each
message your patch is adding, which is IMO the correct approach.

--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
"... In accounting terms this makes perfect sense. To rational humans, it
is insane. Welcome to IBM." (Robert X. Cringely)
https://www.cringely.com/2015/06/03/autodesks-john-walker-explained-hp-and-ibm-in-1991/