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The postmaster is not supposed to do anything that depends fundamentally on shared memory contents, because that creates the risk that a backend crash that trashes shared memory will take the postmaster down with it, preventing automatic recovery. In commit 969d7cd43 I lost sight of this principle and coded AssignPostmasterChildSlot() in such a way that it could fail or even crash if the shared PMSignalState structure became corrupted. Remarkably, we've not seen field reports of such crashes; but I managed to induce one while testing the recent changes around palloc chunk headers. To fix, make a semi-duplicative state array inside the postmaster so that we need consult only local state while choosing a "child slot" for a new backend. Ensure that other postmaster-executed routines in pmsignal.c don't have critical dependencies on the shared state, either. Corruption of PMSignalState might now lead ReleasePostmasterChildSlot() to conclude that backend X failed, when actually backend Y was the one that trashed things. But that doesn't matter, because we'll force a cluster-wide reset regardless. Back-patch to all supported branches, since this is an old bug. Discussion: https://postgr.es/m/3436789.1665187055@sss.pgh.pa.us
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/.