| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Stephen Frost <sfrost(at)snowman(dot)net> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Posix Shared Mem patch |
| Date: | 2012-06-27 14:27:48 |
| Message-ID: | CA+TgmoYcZfpAOMR1MELpMBFeRftaENF8tZKQMK2YXnNN6TBVcQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Jun 27, 2012 at 9:52 AM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> What this all boils down to is- can you have a shm segment that goes
> away when no one is still attached to it, but actually give it a name
> and then detect if it already exists atomically on startup on
> Linux/Unixes? If so, perhaps we could use the same mechanism on both..
As I understand it, no. You can either have anonymous shared
mappings, which go away when no longer in use but do not have a name.
Or you can have POSIX or sysv shm, which have a name but do not
automatically go away when no longer in use. There seems to be no
method for setting up a segment that both has a name and goes away
automatically. POSIX shm in particular tries to "look like a file",
whereas anonymous memory tries to look more like malloc (except that
you can share the mapping with child processes).
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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