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CheckBuffer() is designed to be a concurrent-safe function able to run sanity checks on a relation page without loading it into the shared buffers. The operation is done using a lock on the partition involved in the shared buffer mapping hashtable and an I/O lock for the buffer itself, preventing the risk of false positives due to any concurrent activity. The primary use of this function is the detection of on-disk corruptions for relation pages. If a page is found in shared buffers, the on-disk page is checked if not dirty (a follow-up checkpoint would flush a valid version of the page if dirty anyway), as it could be possible that a page was present for a long time in shared buffers with its on-disk version corrupted. Such a scenario could lead to a corrupted cluster if a host is plugged off for example. If the page is not found in shared buffers, its on-disk state is checked. PageIsVerifiedExtended() is used to apply the same sanity checks as when a page gets loaded into shared buffers. This function will be used by an upcoming patch able to check the state of on-disk relation pages using a SQL function. Author: Julien Rouhaud, Michael Paquier Reviewed-by: Masahiko Sawada Discussion: https://postgr.es/m/CAOBaU_aVvMjQn=ge5qPiJOPMmOj5=ii3st5Q0Y+WuLML5sR17w@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/.