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A very common usage pattern is that we set a timeout that we don't expect to reach, cancel it after a little bit, and later repeat. With the original implementation of timeout.c, this results in one setitimer() call per timeout set or cancel. We can do a lot better by being lazy about changing the timeout interrupt request, namely: (1) never cancel the outstanding interrupt, even when we have no active timeout events; (2) if we need to set an interrupt, but there already is one pending at or before the required time, leave it alone. When the interrupt happens, the signal handler will reschedule it at whatever time is then needed. For example, with a one-second setting for statement_timeout, this method results in having to interact with the kernel only a little more than once a second, no matter how many statements we execute in between. The mainline code might never call setitimer() at all after the first time, while each time the signal handler fires, it sees that the then-pending request is most of a second away, and that's when it sets the next interrupt request for. Each mainline timeout-set request after that will observe that the time it wants is past the pending interrupt request time, and do nothing. This also works pretty well for cases where a few different timeout lengths are in use, as long as none of them are very short. But that describes our usage well. Idea and original patch by Thomas Munro; I fixed a race condition and improved the comments. Discussion: https://postgr.es/m/CA+hUKG+o6pbuHBJSGnud=TadsuXySWA7CCcPgCt2QE9F6_4iHQ@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/.