7e6fb5da41
e0b1ee17dc introduced optimization for matching B-tree scan keys required for the directional scan. However, it incorrectly assumed that all keys required for opposite direction scan are satisfied by _bt_first(). It has been illustrated that with multiple scan keys over the same column, a lesser one (according to the scan direction) could win leaving the other one unsatisfied. Instead of relying on _bt_first() this commit introduces code that memorizes whether there was at least one match on the page. If that's true we know that keys required for opposite-direction scan are satisfied as soon as corresponding values are not NULLs. Also, this commit simplifies the description for the optimization of keys required for the current direction scan. Now the flag used for this is named continuescanPrechecked and means exactly that *continuescan flag is known to be true for the last item on the page. Reported-by: Peter Geoghegan Discussion: https://postgr.es/m/CAH2-Wzn0LeLcb1PdBnK0xisz8NpHkxRrMr3NWJ%2BKOK-WZ%2BQtTQ%40mail.gmail.com Reviewed-by: Pavel Borisov
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/.