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The reason for doing so is that it will allow expression evaluation to optimize based on the underlying tupledesc. In particular it will allow to JIT tuple deforming together with the expression itself. For that expression initialization needs to be moved after the relevant slots are initialized - mostly unproblematic, except in the case of nodeWorktablescan.c. After doing so there's no need for ExecAssignResultType() and ExecAssignResultTypeFromTL() anymore, as all former callers have been converted to create a slot with a fixed descriptor. When creating a slot with a fixed descriptor, tts_values/isnull can be allocated together with the main slot, reducing allocation overhead and increasing cache density a bit. Author: Andres Freund Discussion: https://postgr.es/m/20171206093717.vqdxe5icqttpxs3p@alap3.anarazel.de
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/.