3b1a7eb289
Since 66c0185a3, the planner is able to use Merge Append -> Unique to implement UNION queries and each subquery is prompted to produce Paths correctly sorted by the UNION's targetlist. Here we remove some now redundant code which was zeroing the tuple_fraction at the parent level. This will allow the planner to consider cheap startup paths when planning the UNION's subqueries. EXCEPT and INTERSECT set operations still have the tuple_fraction zeroed in generate_nonunion_paths(). These operations currently always read all of their subqueries' tuples. Reported-by: Tom Lane Discussion: https://postgr.es/m/3703023.1711654574@sss.pgh.pa.us
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.