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After the WAL format changes, the calculation of the size of a checkpoint record became incorrect. Instead of trying to fix the math, check that the previous record, i.e. the xl_prev value that we'd write for the next record, matches the last checkpoint's redo pointer. That way it's not dependent on the size of the checkpoint record at all. The old logic was actually slightly wrong all along: if the previous checkpoint record crossed a page boundary, the page headers threw off the record size calculation, and the checkpoint was not skipped. The new checkpoint would not cross a page boundary, so this only resulted in at most one extra checkpoint after the system became idle. The new logic fixes that. (It's not worth fixing in backbranches). However, it makes some sense to try to keep the latest checkpoint contained fully in a page, or at least in a single WAL segment, just on general robustness grounds. If something goes awfully wrong, it's more likely that you can recover the latest WAL segment, than the last two WAL segments. So I added an extra check that the checkpoint is not skipped if the previous checkpoint crossed a WAL segment. Reported by Jeff Janes. |
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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/.