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Starting with commit 7db0cd2145f, RelationGetBufferForTuple() did a visibilitymap_pin() while holding an exclusive buffer content lock on a newly extended page, when using COPY FREEZE. We elsewhere try hard to avoid to doing IO while holding a content lock. And until 14f98e0af99, that happened while holding the relation extension lock. Practically, this isn't a huge issue, because COPY FREEZE is restricted to relations created or truncated in the current session, so it's unlikely there's a lot of contention. We can't avoid doing IO while holding the content lock by pinning the VM earlier, because we don't know which page it will be on. While we could just ignore the issue in this case, a future commit will add bulk relation extension, which needs to enter pages into the FSM while also trying to hold onto a buffer lock. To address this issue, use visibilitymap_pin_ok() to see if the relevant buffer is already pinned. If not, release the buffer, pin the VM buffer, and acquire the lock again. This opens up a small window for other backends to insert data onto the page - as the page is not entered into the freespacemap, other backends won't see it normally, but a concurrent vacuum could enter the page, if it started just after the relation is extended. In case the page is used by another backend, retry. This is very similar to how locking "otherBuffer" is already dealt with. Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com> Discussion: http://postgr.es/m/20230325025740.wzvchp2kromw4zqz@awork3.anarazel.de
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/.