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On Linux, we call posix_fallocate() on shm_open()'d memory to avoid later potential SIGBUS (see commit 899bd785). Based on field reports of systems stuck in an EINTR retry loop there, there, we made it possible to break out of that loop via slightly odd coding where the CHECK_FOR_INTERRUPTS() call was somewhat removed from the loop (see commit 422952ee). On further reflection, that was not a great choice for at least two reasons: 1. If interrupts were held, the CHECK_FOR_INTERRUPTS() would do nothing and the EINTR error would be surfaced to the user. 2. If EINTR was reported but neither QueryCancelPending nor ProcDiePending was set, then we'd dutifully retry, but with a bit more understanding of how posix_fallocate() works, it's now clear that you can get into a loop that never terminates. posix_fallocate() is not a function that can do some of the job and tell you about progress if it's interrupted, it has to undo what it's done so far and report EINTR, and if signals keep arriving faster than it can complete (cf recovery conflict signals), you're stuck. Therefore, for now, we'll simply block most signals to guarantee progress. SIGQUIT is not blocked (see InitPostmasterChild()), because its expected handler doesn't return, and unblockable signals like SIGCONT are not expected to arrive at a high rate. For good measure, we'll include the ftruncate() call in the blocked region, and add a retry loop. Back-patch to all supported releases. Reported-by: Alvaro Herrera <alvherre@alvh.no-ip.org> Reported-by: Nicola Contu <nicola.contu@gmail.com> Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org> Reviewed-by: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/20220701154105.jjfutmngoedgiad3%40alvherre.pgsql
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/.