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

On Thu, 6 Aug 2009, Shawn O. Pearce wrote:

A Large Angry SCM [off-list ref] wrote:

quoted

Shawn O. Pearce wrote:

quoted

Nick Edelen [off-list ref] wrote:

quoted

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.

FWIW it was this redundancy in duplicate (unpacked) string redundancy 
I meant, but I did a poor job at expressing myself, and consequently Nick 
did not understand what I want (and I'm on a slow connection, so I deleted 
the mail halfway through looking if there are some real answers hidden in 
the huge quoted part instead of replying).

And the fragility of the dependency to the implementation detail of the 
pack index suggests to me that my intuition that this whole thing should 
be more tightly integrated with the pack index was not totally off the 
mark.

Ciao,
Dscho