Re: WIP patch for parallel pg_dump

We may need other means to ensure that the snapshot is available on
the slave. It could be a bit too early to use the snapshot on the
slave depending upon the delay of WAL replay.
----------
Koichi Suzuki

2010/12/7 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> 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
>
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