On Thu, Oct 24, 2013 at 6:03 PM, Jeff King <p...@peff.net> wrote:
> If `prepare_bitmap_walk` runs successfully, the resulting bitmap is
> stored and the equivalent of a `traverse_commit_list` call can be
> performed by using `traverse_bitmap_commit_list`; the bitmap version
> of this call yields the objects straight from the packfile index
> (without having to look them up or parse them) and hence is several
> orders of magnitude faster.

This is interesting, we didn't attempt it in JGit, but I can see how
it could be very useful.

> As an extra optimization, when `prepare_bitmap_walk` succeeds, the
> `reuse_partial_packfile_from_bitmap` call can be attempted: it will find
> the amount of objects at the beginning of the on-disk packfile that can
> be reused as-is, and return an offset into the packfile. The source
> packfile can then be loaded and the bytes up to `offset` can be written
> directly to the result without having to consider the entires inside the
> packfile individually.

Yay! This is similar to the optimization we use in JGit to send the
entire pack, but the part about sending a leading prefix is new. Do
you have any data showing how well this works in practice for cases
where offset is before than length-20?
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