Re: pgsql: postgres_fdw: Add ORDER BY to some remote SQL queries.

On Tue, Nov  3, 2015 at 06:05:11PM +0000, Robert Haas wrote:
> postgres_fdw: Add ORDER BY to some remote SQL queries.
>
> If the join problem's entire ORDER BY clause can be pushed to the
> remote server, consider a path that adds this ORDER BY clause.  If
> use_remote_estimate is on, we cost this path using an additional
> remote EXPLAIN.  If not, we just estimate that the path costs 20%
> more, which is intended to be large enough that we won't request a
> remote sort when it's not helpful, but small enough that we'll have
> the remote side do the sort when in doubt.  In some cases, the remote
> sort might actually be free, because the remote query plan might
> happen to produce output that is ordered the way we need, but without
> remote estimates we have no way of knowing that.
>
> It might also be useful to request sorted output from the remote side
> if it enables an efficient merge join, but this patch doesn't attempt
> to handle that case.

Does this complete FDW join pushdown?

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  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
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