From 7e012ad84fc51fbcd5edbddd951a74fd3f264f66 Mon Sep 17 00:00:00 2001
From: Martin von Zweigbergk <martinvonz@google.com>
Date: Sun, 7 Feb 2021 23:45:14 -0800
Subject: [PATCH] log: use index for walking revisions

This updates `jj log` to walk the index for doing the topological
walk, which is much faster than walking the object graph. This speeds
up `jj log | head -1` in the git.git repo from ~1.9s to ~0.27s (most
of the remaining time is spent calculating the evolve state).

A consequence of walking the index instead is that the order of
commits in the output is by by generation number. That's nice in some
ways, but it also means that the newest commit isn't always at the
top.
---
 src/commands.rs | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/src/commands.rs b/src/commands.rs
index 7ce478d01..139c3a9e3 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -1049,27 +1049,24 @@ fn cmd_log(
     let mut styler = styler.as_mut();
     styler.add_label(String::from("log"));
 
+    let store = repo.store();
     let mut heads: HashSet<_> = repo
         .view()
         .heads()
         .iter()
-        .map(|id| repo.store().get_commit(id).unwrap())
+        .map(|id| store.get_commit(id).unwrap())
         .collect();
     if !sub_matches.is_present("all") {
         heads = skip_uninteresting_heads(&repo, heads);
     };
-    let mut heads: Vec<_> = heads.into_iter().collect();
-    heads.sort_by_key(|commit| commit.committer().timestamp.clone());
-    heads.reverse();
 
-    let commits = topo_order_reverse(
-        heads,
-        Box::new(|commit: &Commit| commit.id().clone()),
-        Box::new(|commit: &Commit| commit.parents()),
-    );
+    let head_ids: Vec<_> = heads.iter().map(|commit| commit.id().clone()).collect();
+    let index = repo.index();
+    let index_entries = index.walk_revs(&head_ids, &[]);
     if use_graph {
         let mut graph = AsciiGraphDrawer::new(&mut styler);
-        for commit in commits {
+        for index_entry in index_entries {
+            let commit = store.get_commit(&index_entry.commit_id()).unwrap();
             let mut edges = vec![];
             for parent in commit.parents() {
                 edges.push(Edge::direct(parent.id().clone()));
@@ -1087,7 +1084,8 @@ fn cmd_log(
             graph.add_node(commit.id(), &edges, b"o", &buffer);
         }
     } else {
-        for commit in commits {
+        for index_entry in index_entries {
+            let commit = store.get_commit(&index_entry.commit_id()).unwrap();
             template.format(&commit, styler);
         }
     }