On Mon, Jun 8, 2015 at 1:51 PM, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote: > Robert Haas wrote: > >> After studying this, I think it's a bug. See this comment: >> >> * Normal child backends can only be launched when we are in PM_RUN or >> * PM_HOT_STANDBY state. (We also allow launch of normal >> * child backends in PM_WAIT_BACKUP state, but only for superusers.) >> * In other states we handle connection requests by launching "dead_end" >> * child processes, which will simply send the client an error message and >> * quit. (We track these in the BackendList so that we can know when they >> * are all gone; this is important because they're still connected to shared >> * memory, and would interfere with an attempt to destroy the shmem segment, >> * possibly leading to SHMALL failure when we try to make a new one.) >> * In PM_WAIT_DEAD_END state we are waiting for all the dead_end children >> * to drain out of the system, and therefore stop accepting connection >> * requests at all until the last existing child has quit (which hopefully >> * will not be very long). >> >> That comment seems to imply that, at the very least, all backends with >> shared-memory access need to be part of BackendList. But really, I'm >> unclear why we'd ever want to exit without all background workers >> having shut down, so maybe they should all be in there. Isn't that >> sorta the point of this facility? >> >> Alvaro, any thoughts? > > As I recall, my thinking was: > > * anything connected to shmem that crashes could leave things in bad > state (for example locks improperly held), whereas things not connected > to shmem could crash without it being a problem for the rest of the > system and thus do not require a full restart cycle. This stuff is > detected with the PMChildSlot thingy; therefore all bgworkers with shmem > access should have one of these. > > * I don't recall offhand what the criteria is for stuff to be in > postmaster's BackendList. According to the comment on top of struct > Backend, bgworkers connected to shmem should be on that list, even if > they did not have the BGWORKER_BACKEND_DATABASE_CONNECTION flag on > registration. So that would be a bug. > > Does this help you any?
Well, it sounds like we at least need to think about making it consistently depend on shmem-access rather than database-connection. I'm less sure what to do with workers that have not even got shmem access. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
