Re: WIP patch for parallel pg_dump

marcin mank <marcin(dot)mank(at)gmail(dot)com> writes:
> On Sun, Dec 5, 2010 at 7:28 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> IIRC, in old discussions of this problem we first considered allowing
>> clients to pull down an explicit representation of their snapshot (which
>> actually is an existing feature now, txid_current_snapshot()) and then
>> upload that again to become the active snapshot in another connection.

> Could a hot standby use such a snapshot representation? I.e. same
> snapshot on the master and the standby?

Hm, that's a good question. It seems like it's at least possibly
workable, but I'm not sure if there are any showstoppers. The other
proposal of publish-a-snapshot would presumably NOT support this, since
we'd not want to ship the snapshot temp files down the WAL stream.

However, if you were doing something like parallel pg_dump you could
just run the parent and child instances all against the slave, so the
pg_dump scenario doesn't seem to offer much of a supporting use-case for
worrying about this. When would you really need to be able to do it?

regards, tom lane