55a780e947
For an ordered Append or MergeAppend, we need to inject an explicit sort into any subpath that is not already well enough ordered. Currently, only explicit full sorts are considered; incremental sorts are not yet taken into account. In this patch, for subpaths of an ordered Append or MergeAppend, we choose to use explicit incremental sort if it is enabled and there are presorted keys. The rationale is based on the assumption that incremental sort is always faster than full sort when there are presorted keys, a premise that has been applied in various parts of the code. In addition, the current cost model tends to favor incremental sort as being cheaper than full sort in the presence of presorted keys, making it reasonable not to consider full sort in such cases. No backpatch as this could result in plan changes. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: Andrei Lepikhov <lepihov@gmail.com> Reviewed-by: Robert Haas <robertmhaas@gmail.com> Discussion: https://postgr.es/m/CAMbWs4_V7a2enTR+T3pOY_YZ-FU8ZsFYym2swOz4jNMqmSgyuw@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.
Copyright and license information can be found in the file COPYRIGHT.
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