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When diffing two trees, we currently start at the root and diff those trees. Then we diff each subtree, one at a time, recursively. When using a commit backend that uses remote storage, like our backend at Google does, diffing the subtrees one at a time gets very slow. We should be able to diff subtrees concurrently. That way, the number of roundtrips to a server becomes determined by the depth of the deepest difference instead of by the number of differing trees (times 2, even). This patch implements such an algorithm behind a `Stream` interface. It's not hooked in to `MergedTree::diff_stream()` yet; that will happen in the next commit. I timed the new implementation by updating `jj diff -s` to use the new diff stream and then ran it on the Linux repo with `jj diff --ignore-working-copy -s --from v5.0 --to v6.0`. That slowed down by ~20%, from ~750 ms to ~900 ms. Maybe we can get some of that performance back but I think it'll be hard to match `MergedTree::diff()`. We can decide later if we're okay with the difference (after hopefully reducing the gap a bit) or if we want to keep both implementations. I also timed the new implementation on our cloud-based repo at Google. As expected, it made some diffs much faster (I'm not sure if I'm allowed to share figures). |
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| benches | ||
| gen-protos | ||
| src | ||
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| testutils | ||
| Cargo.toml | ||
| LICENSE | ||