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Such an access became possible when commit 246a6c8f7 added more aggressive cleanup of orphaned temp relations by autovacuum. Since autovacuum's snapshot might be slightly stale, it could attempt to access an already-dropped temp namespace, resulting in an assertion failure or null-pointer dereference. (In practice, since we don't drop temp namespaces automatically but merely recycle them, this situation could only arise if a superuser does a manual drop of a temp namespace. Still, that should be allowed.) The core of the bug, IMO, is that isTempNamespaceInUse and its callers failed to think hard about whether to treat "temp namespace isn't there" differently from "temp namespace isn't in use". In hopes of forestalling future mistakes of the same ilk, replace that function with a new one checkTempNamespaceStatus, which makes the same tests but returns a three-way enum rather than just a bool. isTempNamespaceInUse is gone entirely in HEAD; but just in case some external code is relying on it, keep it in the back branches, as a bug-compatible wrapper around the new function. Per report originally from Prabhat Kumar Sahu, investigated by Mahendra Singh and Michael Paquier; the final form of the patch is my fault. This replaces the failed fix attempt in a052f6cbb. Backpatch as far as v11, as 246a6c8f7 was. Discussion: https://postgr.es/m/CAKYtNAr9Zq=1-ww4etHo-VCC-k120YxZy5OS01VkaLPaDbv2tg@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/.