Re: User feedback: raise the default leaf size to 16k

[Chris Mason <chris.mason@fusionio.com>]

On Sun, Mar 03, 2013 at 03:33:30AM -0700, Brendan Hide wrote:
> On 2013/02/13 12:33 PM, Holger Hoffstaette wrote:
> > - raise the leaf size to 16k
> > - use single metadata profile
> >
> > ...
> >
> > the difference in behaviour on a single disk is *very* noticeable.
> Did you try an isolated change of leaf size? I think the devs would be 
> willing to look into the default size if it makes a dramatic difference 
> on its own. Personally I think you are seeing an improvement more as a 
> result of the metadata profile rather than the leafsize.
> 
> I don't think changing the default profile for metadata will be easily 
> entertained as this is very important for protecting against corruption 
> due to bitrot.

The long term plan is to set the default size to 16K, since this does
cut down on metadata fragmentation.  But in some benchmarks, it adds lock
contention because we have fewer blocks to spread the locks over.

The 3.9 merge window has fixes for lock contention, so I need to
benchmark things again.

-chris