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Re: Nameless IPC on POSIX systems

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: des(at)des(dot)no (=?iso-8859-1?q?Dag-Erling_Sm=F8rgrav?=)
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: Nameless IPC on POSIX systems
Date: 2005-05-06 19:51:24
Message-ID: 17797.1115409084@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
des(at)des(dot)no (=?iso-8859-1?q?Dag-Erling_Sm=F8rgrav?=) writes:
> You can use file-backed shared memory instead.  You need a directory
> which you know is writeable and unique to this instance, on a file
> system with enough free space to accomodate the full size of the
> shared memory segment.  DataDir is probably a good choice.  If the
> file does not exist, you create it at startup.  If it does exist, you
> map it in and perform the same checks as in the SysV case.

The check we need is "are there any other processes (still) attached to
this shmem" and AFAIK that is not available in the mmap API.  Do you
know how to get it?

> Anyway, I'm not sure you fully understand the problem this patch
> addresses.

Yes, I do.  I'm not interested in substituting a risk of data corruption
for them.

			regards, tom lane

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