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Document VACUUM's soft assumption that any LP_DEAD items encountered during pruning will become LP_UNUSED items before VACUUM finishes up. This is integral to the accounting used by VACUUM to generate its final report on the table to the stats collector. It also affects how VACUUM determines which heap pages are truncatable. In both cases VACUUM is concerned with the likely contents of the page in the near future, not the current contents of the page. This state of affairs created the false impression that VACUUM's dead tuple accounting had significant difference with similar accounting used during ANALYZE. There were and are no substantive differences, at least when the soft assumption completely works out. This is far clearer now. Also document cases where things don't quite work out for VACUUM's dead tuple accounting. It's possible that a significant number of LP_DEAD items will be left behind by VACUUM, and won't be recorded as remaining dead tuples in VACUUM's statistics collector report. This behavior dates back to commit a96c41fe, which taught VACUUM to run without index and heap vacuuming at the user's request. The failsafe mechanism added to VACUUM more recently by commit 1e55e7d1 takes the same approach to dead tuple accounting. Reported-By: Masahiko Sawada <sawada.mshk@gmail.com> Discussion: https://postgr.es/m/CAH2-Wz=Jmtu18PrsYq3EvvZJGOmZqSO2u3bvKpx9xJa5uhNp=Q@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/.