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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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| .. | ||
| test_bad_locking.rs | ||
| test_commit_builder.rs | ||
| test_commit_concurrent.rs | ||
| test_conflicts.rs | ||
| test_default_revset_graph_iterator.rs | ||
| test_diff_summary.rs | ||
| test_git.rs | ||
| test_id_prefix.rs | ||
| test_index.rs | ||
| test_init.rs | ||
| test_load_repo.rs | ||
| test_local_working_copy.rs | ||
| test_local_working_copy_concurrent.rs | ||
| test_local_working_copy_sparse.rs | ||
| test_merge_trees.rs | ||
| test_merged_tree.rs | ||
| test_mut_repo.rs | ||
| test_operations.rs | ||
| test_refs.rs | ||
| test_revset.rs | ||
| test_rewrite.rs | ||
| test_view.rs | ||
| test_workspace.rs | ||