Re: WIP patch for parallel pg_dump

Josh Berkus <josh@agliodbs.com> writes:
>> 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?

> If you had several standbys, you could distribute the work of the
> pg_dump among them.  This would be a huge speedup for a large database,
> potentially, thanks to parallelization of I/O and network.  Imagine
> doing a pg_dump of a 300GB database in 10min.

That does sound kind of attractive.  But to do that I think we'd have to
go with the pass-the-snapshot-through-the-client approach.  Shipping
internal snapshot files through the WAL stream doesn't seem attractive
to me.

While I see Robert's point about preferring not to expose the snapshot
contents to clients, I don't think it outweighs all other considerations
here; and every other one is pointing to doing it the other way.

			regards, tom lane