On 2015/09/11 6:24, Robert Haas wrote:
On Thu, Sep 3, 2015 at 1:22 AM, Etsuro Fujita
<fujita.ets...@lab.ntt.co.jp> wrote:
I'm wondering if there's another approach.  If I understand correctly,
there are two reasons why the current situation is untenable.  The
first is that ForeignRecheck always returns true, but we could instead
call an FDW-supplied callback routine there.  The callback could be
optional, so that we just return true if there is none, which is nice
for already-existing FDWs that then don't need to do anything.


My question about this is, is the callback really needed?  If there are any
FDWs that want to do the work *in their own way*, instead of just doing
ExecProcNode for executing a local join execution plan in case of foreign
join (or just doing ExecQual for checking remote quals in case of foreign
table), I'd agree with introducing the callback, but if not, I don't think
that that makes much sense.

It doesn't seem to me that it hurts much of anything to add the
callback there, and it does provide some flexibility.  Actually, I'm
not really sure why we're thinking we need a subplan here at all,
rather than just having a ForeignRecheck callback that can do whatever
it needs to do with no particular help from the core infrastructure.
I think you wrote some code to show how postgres_fdw would use the API
you are proposing, but I can't find it.  Can you point me in the right
direction?

I've proposed the following API changes:

* I modified create_foreignscan_path, which is called from postgresGetForeignJoinPaths/postgresGetForeignPaths, so that a path, subpath, is passed as the eighth argument of the function. subpath represents a local join execution path if scanrelid==0, but NULL if scanrelid>0.

* I modified make_foreignscan, which is called from postgresGetForeignPlan, so that a list of quals, fdw_quals, is passed as the last argument of the function. fdw_quals represents remote quals if scanrelid>0, but NIL if scanrelid==0.

You can find that code in the postgres_fdw patch (foreign_join_v16_efujita.patch) attached to [1].

Best regards,
Etsuro Fujita

[1] http://www.postgresql.org/message-id/55cb2d45.7040...@lab.ntt.co.jp



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