FreeBSD 10 and PostgreSQL 9.3 scalability issues

Sean Chittenden sean at
Wed Mar 19 23:40:07 UTC 2014

> As far as I know, the test was done on both UFS2 and ZFS and the
> difference was marginal.

As Adrian pointed out, there is an mmap(2) mutex in the way. Starting in PostgreSQL 9.3, shared buffers are allocated out of mmap(2) instead of shm. shm is only used to notify the PostgreSQL postmaster that a child process exited/crashed (when a pid detaches from a shm segment, there is a kernel event, but there is no kernel event when detaching from an mmap(2) region). -sc

>>> Just want to share these pgbench results done by DragonFlyBSD, and would
>>> like some input on why these numbers look so bad and what can be done to
>>> improve (ie. kernel tunables etc) the performance.
>> Do you have the ability to test with FreeBSD 8.x and 9.x to see if this is
>> regression?
>> Also you don't mention the FS used in each case, so I'm wondering if you
>> used a ZFS install of FreeBSD which could help to explain things.

Sean Chittenden
sean at

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