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pg_ctl start with -w previously relied on a heuristic that the postmaster would surely always manage to create postmaster.pid within five seconds. Unfortunately, that fails much more often than we would like on some of the slower, more heavily loaded buildfarm members. We have known for quite some time that we could remove the need for that heuristic on Unix by using fork/exec instead of system() to launch the postmaster. This allows us to know the exact PID of the postmaster, which allows near-certain verification that the postmaster.pid file is the one we want and not a leftover, and it also lets us use waitpid() to detect reliably whether the child postmaster has exited or not. What was blocking this change was not wanting to rewrite the Windows version of start_postmaster() to avoid use of CMD.EXE. That's doable in theory but would require fooling about with stdout/stderr redirection, and getting the handling of quote-containing postmaster switches to stay the same might be rather ticklish. However, we realized that we don't have to do that to fix the problem, because we can test whether the shell process has exited as a proxy for whether the postmaster is still alive. That doesn't allow an exact check of the PID in postmaster.pid, but we're no worse off than before in that respect; and we do get to get rid of the heuristic about how long the postmaster might take to create postmaster.pid. On Unix, this change means that a second "pg_ctl start -w" immediately after another such command will now reliably fail, whereas previously it would succeed if done within two seconds of the earlier command. Since that's a saner behavior anyway, it's fine. On Windows, the case can still succeed within the same time window, since pg_ctl can't tell that the earlier postmaster's postmaster.pid isn't the pidfile it is looking for. To ensure stable test results on Windows, we can insert a short sleep into the test script for pg_ctl, ensuring that the existing pidfile looks stale. This hack can be removed if we ever do rewrite start_postmaster(), but that no longer seems like a high-priority thing to do. Back-patch to all supported versions, both because the current behavior is buggy and because we must do that if we want the buildfarm failures to go away. Tom Lane and Michael Paquier |
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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/.