Re: Foreign join pushdown vs EvalPlanQual

On 2015/10/17 9:58, Robert Haas wrote:
> But with Etsuro Fujita's patch, and I think what you have proposed has
> been similar, how are you going to do it? The proposal is to call the
> recheck method and hope for the best, but what is the recheck method
> going to do? Where is it going to get the previously-returned tuple?

As I explained in a previous email, just returning the
previously-returned tuple is not good enough.

> How will it know if it has already returned it during the lifetime of
> this EPQ check? Offhand, it looks to me like, at least in some
> circumstances, you're probably going to return whatever tuple you
> returned most recently (which has a good chance of being the right
> one, but not necessarily) over and over again. That's not going to
> fly.

No. Since the local join execution plan is created so that the scan
slot for each foreign table involved in the pushed-down join looks at
its EPQ slot, I think the plan can return at most one tuple.

Best regards,
Etsuro Fujita