On Wed, Jan 30, 2019 at 6:12 AM Etsuro Fujita <fujita.ets...@lab.ntt.co.jp> wrote:
> (2018/12/28 15:50), Etsuro Fujita wrote: > > Attached is a new version of the > > patch. > > Here is an updated version of the patch set. Changes are: > > * In the previous version, LIMIT without OFFSET was not performed > remotely as the costs was calculated the same as the costs of performing > it locally. (Actually, such LIMIT was performed remotely in a case in > the postgres_fdw regression test, but that was due to a bug :(.) I > think we should prefer performing such LIMIT remotely as that avoids > extra row fetches from the remote that performing it locally might > cause, so I tweaked the costs estimated in estimate_path_cost_size(), to > ensure that we'll prefer performing such LIMIT remotely. > With your tweaks, I'm still not seeing the ORDER-less LIMIT get pushed down when using use_remote_estimate in a simple test case, either with this set of patches, nor in the V4 set. However, without use_remote_estimate, the LIMIT is now getting pushed with these patches when it does not in HEAD. See attached test case, to be run in new database named 'foo'. Cheers, Jeff
create extension postgres_fdw ; create server foo foreign data wrapper postgres_fdw options (use_remote_estimate 'true', fetch_size '100000'); \! pgbench -i -s20 foo create user MAPPING FOR public SERVER foo ; create schema schema2; import FOREIGN SCHEMA public from server foo into schema2; explain (verbose,analyze) select * from schema2.pgbench_accounts limit 1;
