Re: the number of file descriptors when using POSIX semaphore

flyusa2010 fly wrote:
> Hi, folks,
>
> in src/template/darwin:
>
> # Select appropriate semaphore support. Darwin 6.0 (Mac OS X 10.2) and up
> # support System V semaphores; before that we have to use POSIX semaphores,
> # which are less good for our purposes because they eat a file descriptor
> # per backend per max_connection slot.
>
> To my understanding, the number of descriptors created by POSIX semaphores
> would be # of actual clients times max_connection.
> However, I monitor the number of open files using sysctl, and I find that
> kern.num_files doesn't match the result calculated by the formula that is
> inferred by me...
>
> So, what would the number of file descriptors be, when using POSIX
> semaphore?

I thought the text was wrong, but this commit reinforces that text:

commit 93407d3998cc8717993dbc102f854a478985bc19
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Date: Wed Sep 26 00:32:46 2007 +0000

Use SYSV semaphores rather than POSIX on Darwin >= 6.0
(i.e., OS X 10.2 and up), per Chris Marcellino. This
avoids consuming O(N^2) file descriptors to support N
backends. Tests suggest it's about a wash for small
installations, but large ones would have a problem.

What numbers are you seeing?

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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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