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Deadlock checking was performed inside signal handlers up to now. While it's a remarkable feat to have made this work reliably, it's quite complex to understand why that is the case. Partially it worked due to the assumption that semaphores are signal safe - which is not actually documented to be the case for sysv semaphores. The reason we had to rely on performing this work inside signal handlers is that semaphores aren't guaranteed to be interruptable by signals on all platforms. But now that latches provide a somewhat similar API, which actually has the guarantee of being interruptible, we can avoid doing so. Signalling between ProcSleep, ProcWakeup, ProcWaitForSignal and ProcSendSignal is now done using latches. This increases the likelihood of spurious wakeups. As spurious wakeup already were possible and aren't likely to be frequent enough to be an actual problem, this seems acceptable. This change would allow for further simplification of the deadlock checking, now that it doesn't have to run in a signal handler. But even if I were motivated to do so right now, it would still be better to do that separately. Such a cleanup shouldn't have to be reviewed a the same time as the more fundamental changes in this commit. There is one possible usability regression due to this commit. Namely it is more likely than before that log_lock_waits messages are output more than once. Reviewed-By: Heikki Linnakangas |
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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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.