On 01/07/2015 02:17 AM, Andres Freund wrote:
On 2015-01-06 15:39:29 -0500, Peter Eisentraut wrote:
It wouldn't hurt if we could share SimpleXLogPageRead() between
pg_xlogdump and pg_rewind as the differences are more or less
superficial, but that seems simple enough to achieve by putting a
frontend variant in xlogreader.c/h.
It's not that much code. And although they're almost identical now, it's
not clear that pg_rewind and pg_xlogdump would want the same behaviour
in the future. pg_rewind might want to read files from a WAL archive,
for example. (Not that I have any plans for that right now)
If this ends up shipping, it's going to be a massively popular tool. I
see it as a companion to pg_basebackup. So it should sort of work the
same way. One problem is that it doesn't use the replication protocol,
so the setup is going to be inconsistent with pg_basebackup. Maybe the
replication protocol could be extended to provide the required data.
I'm not particularly bothered by the requirement of also requiring a
normal, not replication, connection. In most cases that'll already be
allowed.
Yeah, it's not a big problem in practice, but it sure would be nice for
usability if it wasn't required. One less thing to document and prepare for.
Maybe something as simple as "give me this file" would work.
Well, looking at libpq_fetch.c it seems there'd be a bit more required.
Not having to create a temporary table on the other side would be nice -
afaics there's otherwise not much stopping this from working against a
standby?
Hmm, that could be done. The temporary table is convenient, but it could
be refactored to work without it.
That might lose the local copy mode, but how important is that?
pg_basebackup doesn't have that mode.
But we have plain pg_start/stop_backup for that case. That alternative
doesn't really exist here.
Also, the local mode works when the server is shut down. The
pg_basebackup analogue of that is just "cp -a $PGDATA backup".
- Heikki
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