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WindowAgg will potentially store large numbers of input rows into tuplestores to allow access to other rows in the frame. If the input is coming via an explicit Sort node, then unneeded columns will already have been discarded (since Sort requests a small tlist); but there are idioms like COUNT(*) OVER () that result in the input not being sorted at all, and cases where the input is being sorted by some means other than a Sort; if we don't request a small tlist, then WindowAgg's storage requirement is inflated by the unneeded columns. Backpatch back to 9.6, where the current tlist handling was added. (Prior to that, WindowAgg would always use a small tlist.) Discussion: https://postgr.es/m/87a7ator8n.fsf@news-spur.riddles.org.uk
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/.