the number of file descriptors when using POSIX semaphore

From: flyusa2010 fly <flyusa2010(at)gmail(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: the number of file descriptors when using POSIX semaphore
Date: 2010-12-06 11:24:27
Message-ID: AANLkTimYkJLjyyWJY4XE6VLDDPn7nqGihHC0fRtmsj+m@mail.gmail.com
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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?

Thanks!

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