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Report on scanned pages within VACUUM VERBOSE and autovacuum logging. These are pages that were physically examined during the VACUUM operation. Note that this can include a small number of pages that were marked all-visible in the visibility map by some earlier VACUUM operation. VACUUM won't skip all-visible pages that aren't part of a range of all-visible pages that's at least 32 blocks in length (partly to avoid missing out on opportunities to advance relfrozenxid during non-aggressive VACUUMs). Commit 44fa8488 simplified the definition of scanned pages. It became the complement of the pages (of those pages from rel_pages) that were skipped using the visibility map. And so scanned pages precisely indicates how effective the visibility map was at saving work. (Before now we displayed the number of pages skipped via the visibility map when happened to be frozen pages, but not when they were merely all-visible, which was less useful to users.) Rename the user-visible OldestXmin output field to "removal cutoff", and show some supplementary information: how far behind the cutoff is (number of XIDs behind) by the time the VACUUM operation finished. This will help users to figure out what's _not_ working in extreme cases where VACUUM is fundamentally unable to remove dead tuples or freeze older tuples (e.g., due to a leaked replication slot). Also report when relfrozenxid is advanced by VACUUM in output that immediately follows "removal cutoff". This structure is intended to highlight the relationship between the new relfrozenxid value for the table, and the VACUUM operation's removal cutoff. Finally, add instrumentation of "missed dead tuples", and the number of pages that had at least one such tuple. These are fully DEAD (not just RECENTLY_DEAD) tuples with storage that could not be pruned due to failure to acquire a cleanup lock on a heap page. This is a replacement for the "skipped due to pin" instrumentation removed by commit 44fa8488. It shows more details than before for pages where failing to get a cleanup lock actually resulted in VACUUM missing out on useful work, but usually shows nothing at all instead (the mere fact that we couldn't get a cleanup lock is usually of no consequence whatsoever now). Author: Peter Geoghegan <pg@bowt.ie> Reviewed-By: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/CAH2-Wznp=c=Opj8Z7RMR3G=ec3_JfGYMN_YvmCEjoPCHzWbx0g@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/.