Since, as has been previously discussed in this forum on multiple occasions [citation needed], the default System V shared memory limits are absurdly low on many systems, the dynamic shared memory patch defaults to POSIX shared memory, which has often been touted as a superior alternative [citation needed]. Unfortunately, the buildfarm isn't entirely happy with this decision. On buildfarm member anole (HP-UX B.11.31), allocation of dynamic shared memory fails with a "Permission denied" error, and on smew (Debian GNU/Linux 6.0), it fails with "Function not implemented", which according to a forum post[1] I found probably indicates that /dev/shm doesn't mount a tmpfs on that box.
What shall we do about this? I see a few options. (1) Define the issue as "not our problem". IOW, as of now, if you want to use PostgreSQL, you've got to either make POSIX shared memory work on your machine, or change the GUC that selects the type of dynamic shared memory used. (2) Default to using System V shared memory. If people want POSIX shared memory, let them change the default. (3) Add a new setting that auto-probes for a type of shared memory that works. Try POSIX first, then System V. Maybe even fall back to mmap'd files if neither of those works. (4) Remove the option to use POSIX shared memory. System V FTW! After some consideration, I think my vote is for option #2. Option #1 seems too user-hostile, especially for a facility that has no in-core users yet, though I can imagine we might want to go that way eventually, especially if we at some point try to dump System V shared memory altogether, as has been proposed. Option #4 seems sad; we know that System V shared memory limits are a problem for plenty of people, so it'd be a shame not to have a way to use the POSIX facilities if they're available. Option #3 is fine as far as it goes, but it adds a significant amount of complexity I'd rather not deal with. Other votes? Other ideas? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company [1] http://forums.justlinux.com/showthread.php?142429-shm_open-problem -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers