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The existing comment explained that a user-created slot could reuse the same shared memory as 'local_slot' during the window between selecting a slot to drop and locking its database, and that we therefore recheck before dropping. It did not, however, spell out the fuller consequence: because local_slot points to a reusable slot-array entry, its fields may already describe a replacement slot, so the earlier drop decision and the slot_database used for locking could relate to an unrelated slot/database. Expand the comment to describe this, and note that the recheck prevents us from dropping a user-created replacement slot while the residual risk (such as briefly locking an unrelated database) is confined to the cycle and is acceptable given the race is rare and non-fatal. No functional change. Author: Fujii Masao <masao.fujii@gmail.com> Author: Xuneng Zhou <xunengzhou@gmail.com> Author: Amit Kapila <amit.kapila16@gmail.com> Discussion: https://postgr.es/m/CAHGQGwGGyEDL3dh7uJ6qPsGvnq4QK_R8+U=12CaprnzwrwaLGA@mail.gmail.com Discussion: https://postgr.es/m/CAHGQGwHqQ1PPVFfYKVxLfRyC-byRdwSN0NeaHj9SLYV97oO5cw@mail.gmail.com |
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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.
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/.