process shared robust mutexes for tdb

[Jeremy Allison]

On Mon, Dec 24, 2012 at 11:39:58AM +0100, Volker Lendecke wrote:
> Hi!
> 
> Under
> 
> http://git.samba.org/?p=vl/samba.git/.git;a=shortlog;h=refs/heads/tdb
> 
> find my current work in progress to augment the fcntl locks
> in tdb with mutexes for the freelist and hash chain locks.
> The reason for this is that fcntl under load pretty much
> collapses. I don't have exact results yet, but the initial
> tests for tdbtorture are spectacular. One test went down
> from 8m47.470s to 0m13.376s. The tdb_open_ex patches are far
> from done. I am still thinking how to protect tdb with
> mutexes from other use. The idea is that this scheme is only
> used for highly contended tdb like locking.tdb where we
> don't do transactions for example.
> 
> Comments?

This looks really clean and nice ! I can believe the
speedup is spectacular :-).

Once I'm back in at work (Jan 3rd) I will play with
this code and try and help get it into mainline.

It looks enough of a win for OEMs that we might
want to have special backport patches for 3.6.x
and 4.0.x to allow production use (one you are
completely happy with it of course).

This is a big win !

Jeremy.