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13a8924ecf
copy_file() reads and writes data 64KB at a time (with default BLCKSZ), and historically has issued a pg_flush_data request after each write. This turns out to interact really badly with macOS's new APFS file system: a large file copy takes over 100X longer than it ought to on APFS, as reported by Brent Dearth. While that's arguably a macOS bug, it's not clear whether Apple will do anything about it in the near future, and in any case experimentation suggests that issuing flushes a bit less often can be helpful on other platforms too. Hence, rearrange the logic in copy_file() so that flush requests are issued once per N writes rather than every time through the loop. I set the FLUSH_DISTANCE to 32MB on macOS (any less than that still results in a noticeable speed degradation on APFS), but 1MB elsewhere. In limited testing on Linux and FreeBSD, this seems slightly faster than the previous code, and certainly no worse. It helps noticeably on macOS even with the older HFS filesystem. A simpler change would have been to just increase the size of the copy buffer without changing the loop logic, but that seems likely to trash the processor cache without really helping much. Back-patch to 9.6 where we introduced msync() as an implementation option for pg_flush_data(). The problem seems specific to APFS's mmap/msync support, so I don't think we need to go further back. Discussion: https://postgr.es/m/CADkxhTNv-j2jw2g8H57deMeAbfRgYBoLmVuXkC=YCFBXRuCOww@mail.gmail.com |
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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/.