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On many modern platforms, /etc/localtime is a symlink to a file within the IANA database. Reading the symlink lets us find out the name of the system timezone directly, without going through the brute-force search embodied in scan_available_timezones(). This shortens the runtime of initdb by some tens of ms, which is helpful for the buildfarm, and it also allows us to reliably select the same zone name the system was actually configured for, rather than possibly choosing one of IANA's many zone aliases. (For example, in a system configured for "Asia/Tokyo", the brute-force search would not choose that name but its alias "Japan", on the grounds of the latter string being shorter. More surprisingly, "Navajo" is preferred to either "America/Denver" or "US/Mountain", as seen in an old complaint from Josh Berkus.) If /etc/localtime doesn't exist, or isn't a symlink, or we can't make sense of its contents, or the contents match a zone we know but that zone doesn't match the observed behavior of localtime(), fall back to the brute-force search. Also, tweak initdb so that it prints the zone name it selected. In passing, replace the last few references to the "Olson" database in code comments with "IANA", as that's been our preferred term since commit b2cbced9e. Patch by me, per a suggestion from Robert Haas; review by Michael Paquier Discussion: https://postgr.es/m/7408.1525812528@sss.pgh.pa.us
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/.