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preadv() and pwritev() are not standardized by POSIX, but appeared in NetBSD in 1999 and were adopted by at least OpenBSD, FreeBSD, DragonFlyBSD, Linux, AIX, illumos and macOS. We don't use them much yet, but an active proposal uses them heavily. In 15, we had two replacement implementations for other OSes: one based on lseek() + -v function if available for true vector I/O, and the other based on a loop over p- function. The former would be an obstacle to hypothetical future multi-threaded code sharing file descriptors, while the latter would not, since commit cf112c12. Furthermore, the number of targeted systems that could benefit from the former's potential upside has dwindled to just one niche OS, since macOS added the functions and we de-supported HP-UX. That doesn't seem like a good trade-off. Therefore, drop the lseek()-based variant, and also the pg_ prefix now that the file position portability hazard is gone. At the time of writing, the only systems in our build farm that lack native preadv/pwritev and thus use fallback code are: * Solaris (but not illumos) * macOS before release 11.0 * Windows With this commit, the above systems will now use the *same* fallback code, the version that loops over pread()/pwrite(). Windows already used that (though a later proposal may include true vector I/O for Windows), so this decision really only affects Solaris, until it gets around to adding these system calls. Also remove some useless includes while here. Reviewed-by: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/CA+hUKGJ3LHeP9w5Fgzdr4G8AnEtJ=z=p6hGDEm4qYGEUX5B6fQ@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. 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/.