0fbfd37cef
Up until now, the only way for a loadable module to disable the use of a particular index was to use build_simple_rel_hook (or, previous to yesterday's commit, get_relation_info_hook) to remove it from the index list. While that works, it has some disadvantages. First, the index becomes invisible for all purposes, and can no longer be used for optimizations such as self-join elimination or left join removal, which can severely degrade the resulting plan. Second, if the module attempts to compel the use of a certain index by removing all other indexes from the index list and disabling other scan types, but the planner is unable to use the chosen index for some reason, it will fall back to a sequential scan, because that is only disabled, whereas the other indexes are, from the planner's point of view, completely gone. While this situation ideally shouldn't occur, it's hard for a loadable module to be completely sure whether the planner will view a certain index as usable for a certain query. If it isn't, it may be better to fall back to a scan using a disabled index rather than falling back to an also-disabled sequential scan. Reviewed-by: Alexandra Wang <alexandra.wang.oss@gmail.com> Discussion: http://postgr.es/m/CA%2BTgmoYS4ZCVAF2jTce%3DbMP0Oq_db_srocR4cZyO0OBp9oUoGg%40mail.gmail.com |
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| configure | ||
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| COPYRIGHT | ||
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| HISTORY | ||
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| README.md | ||
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/.