Re: [PATCH 0/5] Suggested for PU: revision caching system to significantly speed up packing/walking

[A Large Angry SCM <gitzilla@gmail.com>]

Shawn O. Pearce wrote:
> A Large Angry SCM <gitzilla@gmail.com> wrote:
>> Shawn O. Pearce wrote:
>>> Nick Edelen <sirnot@gmail.com> wrote:
>>>> Hrmm, I just realized that it dosn't actually cache paths/names...
>>> You may not need the path name, but instead the hash value that
>>> pack-objects computes from the path name.
>> Please do NOT expose the hash values. The hash used by pack-objects is  
>> an implementation detail of the heuristics used by the _current_ object  
>> packing code. It would be a real shame to have to maintain backward  
>> compatibility with it at some future date after the packing machinery  
>> has changed.
> 
> This is a local cache.  If there was a version number in the header,
> and the hash function changes, we could just bump the version number
> and invalidate all of the caches.
> 
> No sense in storing (and doing IO of) huge duplicate string values
> for something where we really only need 32 bits, and where a
> recompute from scratch only costs a minute.
> 

That will work for me if the cache gets a version number and iff the 
pack-objects hash code gets big warning comments about the cache code 
dependency.