From c98605cc47fe42fac5f685d611db2a0c1afa2fcf Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Thu, 5 Nov 2015 12:05:38 -0500 Subject: Pass extra data to bgworkers, and use this to fix parallel contexts. Up until now, the total amount of data that could be passed to a background worker at startup was one datum, which can be a small as 4 bytes on some systems. That's enough to pass a dsm_handle or an array index, but not much else. Add a bgw_extra flag to the BackgroundWorker struct, allowing up to 128 bytes to be passed to a new worker on any platform. Use this to fix a problem I recently discovered with the parallel context machinery added in 9.5: the master assigns each worker an array index, and each worker subsequently assigns itself an array index, and there's nothing to guarantee that the two sets of indexes match, leading to chaos. Normally, I would not back-patch the change to add bgw_extra, since it is basically a feature addition. However, since 9.5 is still in beta and there seems to be no other sensible way to repair the broken parallel context machinery, back-patch to 9.5. Existing background worker code can ignore the bgw_extra field without a problem, but might need to be recompiled since the structure size has changed. Report and patch by me. Review by Amit Kapila. --- doc/src/sgml/bgworker.sgml | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'doc/src') diff --git a/doc/src/sgml/bgworker.sgml b/doc/src/sgml/bgworker.sgml index ef28f725114..33ff5269516 100644 --- a/doc/src/sgml/bgworker.sgml +++ b/doc/src/sgml/bgworker.sgml @@ -58,6 +58,7 @@ typedef struct BackgroundWorker char bgw_library_name[BGW_MAXLEN]; /* only if bgw_main is NULL */ char bgw_function_name[BGW_MAXLEN]; /* only if bgw_main is NULL */ Datum bgw_main_arg; + char bgw_extra[BGW_EXTRALEN]; int bgw_notify_pid; } BackgroundWorker; @@ -136,6 +137,13 @@ typedef struct BackgroundWorker bgw_main is NULL. + + bgw_extra can contain extra data to be passed + to the background worker. Unlike bgw_main_arg, this data + is not passed as an argument to the worker's main function, but it can be + accessed via MyBgworkerEntry, as discussed above. + + bgw_notify_pid is the PID of a PostgreSQL backend process to which the postmaster should send SIGUSR1 -- cgit v1.2.3