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For the trivial case of iovcnt == 1, kernels are measurably slower at dealing with the more complex arguments of preadv/pwritev than the equivalent plain old pread/pwrite. The overheads are worth it for iovcnt > 1, but for 1 let's just redirect to the cheaper calls. While we could leave it to callers to worry about that, we already have to have our own pg_ wrappers for portability reasons so it seems reasonable to centralize this knowledge there (thanks to Heikki for this suggestion). Try to avoid function call overheads by making them inlinable, which might also allow the compiler to avoid the branch in some cases. For systems that don't have preadv and pwritev (currently: Windows and [closed] Solaris), we might as well pull the replacement functions up into the static inline functions too. Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Discussion: https://postgr.es/m/CA+hUKGJkOiOCa+mag4BF+zHo7qo=o9CFheB8=g6uT5TUm2gkvA@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. 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, 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/.