I wrote:
>> How about getting # of rows estimate by executing EXPLAIN for
>> fully-fledged remote query (IOW, contains pushed-down WHERE clause),
>> estimate selectivity of local filter on the basis of the statistics
>> which are generated by FDW via do_analyze_rel() and FDW-specific
>> sampling function?  In this design, we would be able to use quite
>> correct rows estimate because we can consider filtering stuffs done
>> each side separately, though it requires expensive remote EXPLAIN for
>> each possible path.
> That sounds nice.

... but it still suffers from the problems of local statistics
for remote tables I pointed out.

I think that these shortcomings are not justified by the gain of
one client-server round trip less during planning.  I'd prefer
if pgsql_fdw were not dependent on remote statistics stored in the
local database.

Laurenz Albe

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