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0.01 was unrealistically low as it's the same as the default cpu_tuple_cost and 10x cheaper than the default parallel_tuple_cost. It's hard to imagine a situation where fetching a tuple from a foreign server would be cheaper than fetching one from a parallel worker. After some experimentation on a loopback server, somewhere between 0.15 and 0.3 seems more realistic. Here we split the difference and set it to 0.2. This will cause operations that reduce the number of tuples (e.g. aggregation) to be more likely to take place on the foreign server. Adjusting this causes some plan changes in the postgres_fdw regression tests. This is because penalizing each Path with the additional tuple costs causes some dilution of the costs of the other operations being charged for and results in various paths appearing to be closer to the same costs such that add_path's STD_FUZZ_FACTOR is more likely to see two paths as costing (fuzzily) the same. This isn't ideal, but it shouldn't be reason enough to use artificially low costs. Discussion: https://postgr.es/m/CAApHDvopVjjfh5c1Ed2HRvDdfom2dEpMwwiu5-f1AnmYprJngA@mail.gmail.com |
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.