Performance of tag change

[Matthew D. Fuller]

On Fri, May 29, 2009 at 03:35:14AM -0000 I heard the voice of
Ian Clatworthy, and lo! it spake thus:
> 
> This 5 minute patch drops the time of 'bzr tags' on OOo down from
> 29.3 seconds to 0.4 seconds,

[Landed in bzr.dev:4391]

It also destroys the performance on other trees.

With bzr.dev:4390, doing a `bzr tags` on bzr.dev itself takes about 6
seconds.  With bzr.dev:4391, it takes 5 and a half MINUTES of burning
my CPU into the ground.

I'd guess it's a missing lock making it rebuild the dotted revno
lookup cache for every tag; there are 50 tags on bzr.dev, and it takes
~55x as long to run...


-- 
Matthew Fuller     (MF4839)   |  fullermd at over-yonder.net
Systems/Network Administrator |  http://www.over-yonder.net/~fullermd/
           On the Internet, nobody can hear you scream.