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To be able to guarantee that we can set the hint bit, acquire an exclusive lock on the old buffer. This is required as a future commit will only allow hint bits to be set with a new lock level, which is acquired as-needed in a non-blocking fashion. We need the hint bits, set in heapam_relation_copy_for_cluster() -> HeapTupleSatisfiesVacuum(), to be set, as otherwise reform_and_rewrite_tuple() -> rewrite_heap_tuple() will get confused. Specifically, rewrite_heap_tuple() checks for HEAP_XMAX_INVALID in the old tuple to determine whether to check the old-to-new mapping hash table. It'd be better if we somehow could avoid setting hint bits on the old page. A common reason to use VACUUM FULL is very bloated tables - rewriting most of the old table during VACUUM FULL doesn't exactly help. Reviewed-by: Heikki Linnakangas <heikki.linnakangas@iki.fi> Reviewed-by: Kirill Reshke <reshkekirill@gmail.com> Discussion: https://postgr.es/m/4wggb7purufpto6x35fd2kwhasehnzfdy3zdcu47qryubs2hdz@fa5kannykekr
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.