Re: Better support of exported snapshots with pg_dump

Hi,

On 2014-09-01 10:25:58 +0200, Bernd Helmle wrote:
> --On 1. September 2014 17:00:32 +0900 Michael Paquier
> <michael.paquier@gmail.com> wrote:
> 
> >Currently pg_dump does not allow a user to specify an exported snapshot
> >name that he would like to use for a dump using SET TRANSACTION SNAPSHOT
> >(now pg_export_snapshot is only used for parallel pg_dump within it). I
> >imagine that this would be handy to take a consistent dump of a given
> >database after creating a logical replication slot on it. Thoughts?

Yes, I always wanted that option.

> There was a discussion of this kind of feature some time ago here:
> 
> <http://www.postgresql.org/message-id/CA+U5nMK9+TTCff_-4MfdxWHnASTAuHuq7u7uedD57vaY28AsQA@mail.gmail.com>

I was never convinced of the reasoning in that thread. Possibly things
have changed enough now that logical decoding is in core...

> Not sure if all the arguments holds still true with the appearance of MVCC
> catalog scans.

I don't think they change anything here. The problem is the, pretty
fundamental, problem that you need to know a relation exists before
executing a LOCK ...; on it. During that time somebody can change the
schema.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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