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Implement a data structure that is a List of Bitmapsets, which is essentially a 2-D boolean array except that the rows need not all be the same width. Operations such as union and intersection are meaningful for these, just as they are for Bitmapsets. Eventually we might build many of the same operations that we have written for Bitmapsets, but for the first use-case we just need a few. That first use-case is for antijoin detection: reduce_outer_joins needs to find the set of Vars that are certain to be non-null in a successfully joined (not null-extended) left join row, and also find the set of Vars subject to higher-level IS NULL constraints, and intersect them. We had been doing this by making Lists of the Var nodes and then using list_intersect, which works but is pretty inefficient compared to a bitmapset-like intersection. Potentially it's O(N^2) if there are a lot of Vars involved, which fortunately there generally aren't; still it's not great. Moreover, that method requires the Vars of interest to be exactly equal() in the join condition and the upper IS NULL condition, which is problematic for my WIP patch that labels Vars according to which outer joins have possibly nulled them. Discussion: https://postgr.es/m/892228.1668437838@sss.pgh.pa.us Discussion: https://postgr.es/m/CAMbWs4-mvPPCJ1W6iK6dD5HiNwoJdi6mZp=-7mE8N9Sh+cd0tQ@mail.gmail.com
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/.