PATCH: cache basis inventory in .bzr

[Robert Collins]

On Mon, 2005-12-19 at 12:55 -0600, John A Meinel wrote:
> Aaron Bentley wrote:
> > John A Meinel wrote:
> 
> ...
> 
> >>> It makes perfect sense to me to have a
> >>> remote branch, which has no working tree, still have a basis inventory.
> > 
> > The use case for a working tree basis inventory is to speed up diff,
> > status, commit, and the like.  What's the use case for a branch basis
> > inventory?
> 
> Yeah, I guess I had my thinking off. The basis inventory is well
> defined, but it isn't useful, because you won't need it for comparison.
> So I'll rework it to put get_basis_inventory back into WorkingTree.
> 
> Should get_basis always succeed, even if it isn't cached? That seems
> generally useful to me.

Yes. The caching is not part of the contract here IMO.

> Also, I wish there was some way to mark that the basis-inventory needed
> to be updated. get_basis_inventory() shouldn't be deleting or modifying
> the file (it is a readonly operation, and has to be, because it will be
> called from other readonly operations).
> For now, it should be updated after something happens which modifies it
> (pull/commit).

uhm, in the working tree we have various caches updated during readonly
locks - like the hash cache. I think the basis inventory is analogous to
the hash cache here - it can be atomically updated without corruption.

> The other nice thing would be to read just the first line, and make sure
> it was the right version, before going through the effort of actually
> parsing the inventory.
> I can think of a regex that should do a decent job.
> Is it worth implementing, or is it just a hackish workaround?

Given the low frequency I'd expect mismatches to occur at : hackish
premature optimisation.

Rob
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