Added to TODO: * Improve detection of shared memory segments being used by other FreeBSD jails
http://archives.postgresql.org/pgsql-hackers/2008-01/msg00656.php --------------------------------------------------------------------------- Mischa Sandberg wrote: > Here (@sophos.com) we run machine cluster tests using FreeBSD jails. A > jail is halfway between a chroot and a VM. Jails blow a number of > assumptions about a unix environment: sysv ipc's are global to all > jails; but a process can only "see" other processes also running in the > jail. In fact, the quickest way to tell whether you're running in a jail > is to test for process 1. > > PGSharedMemoryCreate chooses/reuses an ipc key in a reasonable way to > cover previous postmasters crashing and leaving a shm seg behind, > possibly with some backends still running. > > Unfortunately, with multiple jails running PG servers and (due to app > limitations) all servers having same PGPORT, you get the situation that > when jail#2 (,jail#3,...) server comes up, it: > - detects that there is a shm seg with ipc key 5432001 > - checks whether the associated postmaster process exists (with kill -0) > - overwrites the segment created and being used by jail #1 > > There's a workaround (there always is) other than this patch, involving > NAT translation so that the postmasters listen on different ports, but > the outside world sees them each listening on 5432. But that seems > somewhat circuitous. > > I've hacked sysv_shmem.c (in PG 8.0.9) to handle this problem. Given the > trouble that postmaster goes to, to stop shm seg leakage, I'd like to > solicit any opinions on the wisdom of this edge case. If this patch IS > useful, what would be the right level of compile-time restriction > ("#ifdef __FreeBSD__" ???) > > @@ -319,7 +319,8 @@ > > if (makePrivate) /* a standalone backend > shouldn't do this */ > continue; > - > + /* In a FreeBSD jail, you can't "kill -0" a postmaster > + * running in a different jail, so the shm seg might > + * still be in use. Safer to test nattch ? > + */ > + if (kill(1,0) && errno == ESRCH && > !PGSharedMemoryIsInUse(0,NextShmSegID)) > + continue; > if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, > &shmid)) == NULL) > continue; /* can't attach, > not one of mine */ > > End of Patch. > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to [EMAIL PROTECTED] so that your > message can get through to the mailing list cleanly -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://postgres.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
