Jeff King <p...@peff.net> writes: > There are some calculations that git makes repeatedly, even > though the results are invariant for a certain input (e.g., > the patch-id of a certain commit). We can make a space/time > tradeoff by caching these on disk between runs. > > Even though these may be immutable for a certain commit, we > don't want to directly store the results in the commit > objects themselves, for a few reasons: > > 1. They are not necessarily used by all algorithms, so > bloating the commit object might slow down other > algorithms. > > 2. Because they can be calculated from the existing > commits, they are redundant with the existing > information. Thus they are an implementation detail of > our current algorithms, and should not be cast in stone > by including them in the commit sha1. > > 3. They may only be immutable under a certain set of > conditions (e.g., which grafts or replace refs we are > using). Keeping the storage external means we can > invalidate and regenerate the cache whenever those > conditions change.
4. The algorithm used to compute such values could improve over time. The same advantage argument as 3 applies to this case. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
