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Bad things happen if the DBA issues "pg_ctl stop -m fast" before autoprewarm finishes loading its list of blocks to prewarm. The current worker process successfully terminates early, but (if this wasn't the last database with blocks to prewarm) the leader process will just try to launch another worker for the next database. Since the postmaster is now in PM_WAIT_BACKENDS state, it ignores the launch request, and the leader just sits until it's killed manually. This is mostly the fault of our half-baked design for launching background workers, but a proper fix for that is likely to be too invasive to be back-patchable. To ameliorate the situation, fix apw_load_buffers() to check whether SIGTERM has arrived just before trying to launch another worker. That leaves us with only a very narrow window in each worker launch where SIGTERM could occur between the launch request and successful worker start. Another issue is that if the leader process does manage to exit, it unconditionally rewrites autoprewarm.blocks with only the blocks currently in shared buffers, thus forgetting any blocks that we hadn't reached yet while prewarming. This seems quite unhelpful, since the next database start will then not have the expected prewarming benefit. Fix it to not modify the file if we shut down before the initial load attempt is complete. Per bug #16785 from John Thompson. Back-patch to v11 where the autoprewarm code was introduced. Discussion: https://postgr.es/m/16785-c0207d8c67fb5f25@postgresql.org |
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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. 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/.