Re: pg_receivewal starting position

At Tue, 27 Jul 2021 07:50:39 +0200, Ronan Dunklau <ronan(dot)dunklau(at)aiven(dot)io> wrote in
> Hello,
>
> I've notived that pg_receivewal logic for deciding which LSN to start
> streaming at consists of:
> - looking up the latest WAL file in our destination folder, and resume from
> here
> - if there isn't, use the current flush location instead.
>
> This behaviour surprised me when using it with a replication slot: I was
> expecting it to start streaming at the last flushed location from the
> replication slot instead. If you consider a backup tool which will take
> pg_receivewal's output and transfer it somewhere else, using the replication
> slot position would be the easiest way to ensure we don't miss WAL files.
>
> Does that make sense ?
>
> I don't know if it should be the default, toggled by a command line flag, or if
> we even should let the user provide a LSN.

*I* think it is completely reasonable (or at least convenient or less
astonishing) that pg_receivewal starts from the restart_lsn of the
replication slot to use. The tool already decides the clean-start LSN
a bit unusual way. And it seems to me that proposed behavior can be
the default when -S is specified.

> I'd be happy to implement any of that if we agree.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center