Horton

Re: [PATCH] PostgreSQL 9.4 mmap(2) performance regression on FreeBSD...

Sean Chittenden <sean@chittenden.org>

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From: Sean Chittenden <sean@chittenden.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Bruce Momjian <bruce@momjian.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2014-10-14T05:28:16Z
Lists: pgsql-hackers 
> Really?  Why?

Because it was found to be lighter weight.  See §5 (bottom of ppg 8).

https://kib.kiev.ua/kib/pgsql_perf.pdf

> According to the notes in our code, named POSIX semaphores
> are the least attractive of the three Unixoid semaphore APIs we support,
> because they require eating a file descriptor per backend per
> max_connection slot.  That's a lot of FDs in any large configuration.
> FreeBSD's support for SysV semaphores would have to be pretty darn awful
> to make me think this was a good change, and I've not heard complaints
> in that direction before.
> 
> If you meant to propose using *unnamed* POSIX semaphores, that might be
> a reasonable change, but it would still need some supporting evidence.

https://lists.freebsd.org/pipermail/svn-src-stable-10/2014-October/003515.html

-sc


--
Sean Chittenden
sean@chittenden.org