On Wed, Aug 24, 2016 at 1:55 PM, Etsuro Fujita
<fujita.ets...@lab.ntt.co.jp> wrote:
> On 2016/04/04 23:24, Tom Lane wrote:
>> Amit Langote <langote_amit...@lab.ntt.co.jp> writes:
>>> On 2016/04/04 15:17, Rajkumar Raghuwanshi wrote:
>>>> * .Observation: *Prepare statement execution plan is not getting changed
>>>> even after altering foreign table to point to new schema.
>>> I wonder if performing relcache invalidation upon ATExecGenericOptions()
>>> is the correct solution for this problem.  The attached patch fixes the
>>> issue for me.
>> A forced relcache inval will certainly fix it, but I'm not sure if that's
>> the best (or only) place to put it.
>> A related issue, now that I've seen this example, is that altering
>> FDW-level or server-level options won't cause a replan either.  I'm
>> not sure there's any very good fix for that.  Surely we don't want
>> to try to identify all tables belonging to the FDW or server and
>> issue relcache invals on all of them.
> While improving join pushdown in postgres_fdw, I happened to notice that the
> fetch_size option in 9.6 has the same issue.  A forced replan discussed
> above would fix that issue, but I'm not sure that that's a good idea,
> because the fetch_size option, which postgres_fdw gets at GetForeignRelSize,
> is not used for anything in creating a plan.  So, as far as the fetch_size
> option is concerned, a better solution is (1) to consult that option at
> execution time, probably at BeginForeignScan, not at planning time such as
> GetForiegnRelSize (and (2) to not cause that replan when altering that
> option.)  Maybe I'm missing something, though.

As explained in my latest patch, an FDW knows which of the options,
when changed, render a plan invalid. If we have to track the changes
for each option, an FDW will need to consulted to check whether that
options affects the plan or not. That may be an overkill and there is
high chance that the FDW authors wouldn't bother implementing that
hook. Let me know your views on my latest patch on this thread.

Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

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