8939020853
The postmaster keeps signals blocked everywhere except while waiting for something to happen in ServerLoop(). The code expects that the select(2) will be cancelled with EINTR if an interrupt occurs; without that, followup actions that should be performed by ServerLoop() itself will be delayed. However, some platforms interpret the SA_RESTART signal flag as meaning that they should restart rather than cancel the select(2). Worse yet, some of them restart it with the original timeout delay, meaning that a steady stream of signal interrupts can prevent ServerLoop() from iterating at all if there are no incoming connection requests. Observable symptoms of this, on an affected platform such as HPUX 10, include extremely slow parallel query startup (possibly as much as 30 seconds) and failure to update timestamps on the postmaster's sockets and lockfiles when no new connections arrive for a long time. We can fix this by running the postmaster's signal handlers without SA_RESTART. That would be quite a scary change if the range of code where signals are accepted weren't so tiny, but as it is, it seems safe enough. (Note that postmaster children do, and must, reset all the handlers before unblocking signals; so this change should not affect any child process.) There is talk of rewriting the postmaster to use a WaitEventSet and not do signal response work in signal handlers, at which point it might be appropriate to revert this patch. But that's not happening before v11 at the earliest. Back-patch to 9.6. The problem exists much further back, but the worst symptom arises only in connection with parallel query, so it does not seem worth taking any portability risks in older branches. Discussion: https://postgr.es/m/9205.1492833041@sss.pgh.pa.us |
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README
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/.