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Renaming a file using rename(2) is not guaranteed to be durable in face of crashes; especially on filesystems like xfs and ext4 when mounted with data=writeback. To be certain that a rename() atomically replaces the previous file contents in the face of crashes and different filesystems, one has to fsync the old filename, rename the file, fsync the new filename, fsync the containing directory. This sequence is not generally adhered to currently; which exposes us to data loss risks. To avoid having to repeat this arduous sequence, introduce durable_rename(), which wraps all that. Also add durable_link_or_rename(). Several places use link() (with a fallback to rename()) to rename a file, trying to avoid replacing the target file out of paranoia. Some of those rename sequences need to be durable as well. There seems little reason extend several copies of the same logic, so centralize the link() callers. This commit does not yet make use of the new functions; they're used in a followup commit. Author: Michael Paquier, Andres Freund Discussion: 56583BDD.9060302@2ndquadrant.com Backpatch: All supported branches |
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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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.