[RFC] remove versioned_file.enable_cache

[Ian Clatworthy]

Robert Collins wrote:

>> I use vf.enable_cache() inside the fast-import plugin but just for the
>> inventory knit. I can't remember the performance gain exactly but it was
>> noticeable.

I've just retested this on wordpress (528 files, 6100 revisions):

* with the cache enabled, 4 minutes, 10 seconds
* with that line of code removed, 8 minutes, 27 seconds

So the difference is substantial.

> Sounds like you have a bug then; the cache in question would grow very
> large and cause thrashing on big conversions. Oh wait, that happens
> doesn't it :)

Something is certainly happening on large conversions and it might well
be this, or this in combination with other things. My main concern is
the reduction in revision loading speed over time. I'm not seeing memory
pressure even after several days of running an OpenOffice.org import.

Ian C.