Hacker News Reader

Comment by forkandwait | Hacker News Reader

Anybody know of a FreeBSD comparison?

+1 I'd love to see a FreeBSD kernel hacker chime in here.

ZFS enables some interesting things for pgsql:

* http://open-zfs.org/wiki/Performance_tuning#PostgreSQL - it seems like the primarycache setting prevents the double buffering problem that Linux' page cache has

* http://citusdata.com/blog/64-zfs-compression

I run pgsql on FreeBSD/ZFS and have no complaints but am not taxing the system.

I love ZFS, but Oracle is holding it up which is very annoying.

How do you mean? I trust OpenZFS more and in fact would consider it negligent if Oracle wasn't cherry picking OpenZFS bug fixes. Several original Sun engineers including ZFS co-founder Matt Ahrens are involved with OpenZFS.

Yes, as I have elaborated upon at length[1], the ZFS engineers have long-since left Oracle -- and the open community's ZFS (that is, OpenZFS) has become the ZFS of record.

One clarification: Oracle can't actually cherry-pick back OpenZFS bug fixes because they are (ironically) violating the CDDL by not making available source code. This isn't an issue for the code for which they hold copyright -- but that doesn't include any of the bug fixes and features that we've seen in OpenZFS since 2010. And yes, it is absolutely negligent, but of a different sort than you intended...

[1] http://www.youtube.com/watch?v=-zRN7XLCRhc

Cheers Bryan, that's a great one of your talks and thanks for the interesting licensing comedy.

Do you mean they're holding back progress? With OpenZFS on the scene, it's highly likely that the original Sun/Oracle implementation will become irrelevant to everyone apart from users of Oracle's Solaris releases.

other useful resources on using PostgresSQL on a Linux server with a ZFS filesystem:

- http://adpgtech.blogspot.it/2013/04/linuxzfs-is-great.html

- http://wiki.postgresql.org/images/8/86/PostgreSQL_on_ZFS.pdf

- http://lanyrd.com/2013/linuxcon-north-america/scqmfb/

- http://www.postgresql.org/message-id/CAGa5y0NkVLTNGywmZ6YS8O...

FreeBSD has something like

SHMMAXPGS, SHMMAX in postgresql.conf

in the

sysctl.conf kern.ipc.shmall kern.ipc.shmall

I don't think this has any direct influence on performance.

It was necessary to increase the default limits for larger shared_buffers, etc on pgsql prior to 9.3 where SysV shared memory was used, but this was common to many *nix operating systems.

thanks a lot really. I have being use Linux for a while now. Thanks for the update.

Not relevant since PostgreSQL 9.3 as PostgreSQL now uses Posix shared memory / mmap rather that System V.

Aside from the NUMA stuff, the disk buffer issue probably depends on if you're using ZFS or not.

And also whether the kernel is reporting the true block size of the device; xref advanced format drives (what the drive reports and what the drive does can be two different things), SSDs (minimum write size is typically much bigger than the reported block size), SANs. The true underlying block size can sometimes be determined by benchmarking the latency of different write sizes and also unaligned writes of different sizes.

Dragonfly is probably the best BSD to run for database performance.

http://www.dragonflybsd.org/performance/

That chart is 18 months old. FreeBSD 10 got a number of SMP-related improvements (and some for ZFS as well, if I'm not mistaken). It'd be interesting to see an up-to-date comparison with FreeBSD 10 (and maybe 11-CURRENT), DragonFlyBSD 3.6, and NetBSD 6.1 (and maybe a couple of Linux distros for good measure).

Reply on news.ycombinator.com