Re: no universally correct setting for fsync

Josh Berkus wrote:
>> The real question is how much of a speed-up fsync provides compared to
>> the same workload with synchronous_commit disabled.  The only case for
>> fsync=off is one where that number is much faster.  
>>     
> I can't say I've tested this.  Most of my head-to-heads on fsync were
> before asych existed.
>   

Ditto for me.  Curious about that, and I'd like to help work on 
improving this chunk of the docs too.  I don't know about you guys, but 
I'm swamped until after PGCon though.

I have some hardware testing stuff planned anyway later this month, can 
check exactly where this situation truly stands on a couple of common 
pieces of hardware (next system has one of the LSI controllers Dell 
rebrands too).  I'll have the systems setup for something similar 
anyway--can certainly see fsync differences with pgbench--easy to throw 
this test into the mix too.

With that report, we should have the info needed to really nail this 
down accurately.  I can make my own proofreading pass of what Josh has 
already been doing that also reflects the new data, and then we can 
commit something that's good and well reviewed for 9.0 here.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us