FreeBSD 10 and PostgreSQL 9.3 scalability issues

[Palle Girgensohn]

Den torsdagen den 20:e mars 2014 kl. 00:33:10 UTC+1 skrev Sean Chittenden:
>
> > 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 
>
> http://www.postgresql.org/docs/9.3/static/release-9-3.html#AEN115039 
>
>
> >>> 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. 
> >>> 
> >>> 
> http://lists.dragonflybsd.org/pipermail/users/attachments/20140310/4250b961/attachment-0001.pdf 
> >>> 
> >> 
> >> 
> >> 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 
> se... at chittenden.org <javascript:> 
>
>
>
Hi,

There is a fresh thread about this in postgresql-hackers [1]. 

There are two parallel approaches suggested there, where one is to have an 
option to continue using the old SYSV shared memory in PostgreSQL, and the 
other is the suggestion that "somebody needs to hold the FreeBSD folks' 
feet to the fire about when we can expect to see a fix from their side."

Looking at the original post in this thread, it seems to me that FreeBSD 
has scalability problems beyond what the SYSV vs mmap change in PostgreSQL 
introduces? Check my test of PostgreSQL 9.2 vs 9.3 on FreeBSD 10.0 at [1]. 
The difference between PG92 and PG93 is not huge, ~17%. The difference 
between FreeBSD and the other OS:es in this thread's original post's 
performance chart seems to be about a lot more?

Palle

[1] 
http://www.postgresql.org/message-id/2AE143D2-87D3-4AD1-AC78-CE2258230C05@FreeBSD.org