From 879f585b21e870363f50a161ecfe20a42bce85c9 Mon Sep 17 00:00:00 2001
From: Yuya Nishihara <yuya@tcha.org>
Date: Fri, 20 Jan 2023 16:42:04 +0900
Subject: [PATCH] repo: leverage stored index to calculate shortest prefix in
 commit id space
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With my "jj" work repo, this saves ~4ms to show the log with default revset.

Command:
    JJ_CONFIG=/dev/null hyperfine --warmup 3 --runs 100 \
      "jj log -T 'commit_id.short_prefix_and_brackets() \
                  change_id.short_prefix_and_brackets()' \
              --no-commit-working-copy"

Baseline (a7541e1ba4):
    Time (mean ± σ):      54.1 ms ±  16.4 ms    [User: 46.4 ms, System: 7.8 ms]
    Range (min … max):    36.5 ms …  78.1 ms    100 runs

This commit:
    Time (mean ± σ):      49.5 ms ±  16.4 ms    [User: 42.4 ms, System: 7.2 ms]
    Range (min … max):    31.4 ms …  70.9 ms    100 runs
---
 lib/src/repo.rs | 23 ++++-------------------
 1 file changed, 4 insertions(+), 19 deletions(-)

diff --git a/lib/src/repo.rs b/lib/src/repo.rs
index b63e6db7c..f15c27b32 100644
--- a/lib/src/repo.rs
+++ b/lib/src/repo.rs
@@ -102,7 +102,6 @@ pub struct ReadonlyRepo {
     index_store: Arc<IndexStore>,
     index: OnceCell<Arc<ReadonlyIndex>>,
     // TODO: This should eventually become part of the index and not be stored fully in memory.
-    commit_id_index: OnceCell<IdIndex>,
     change_id_index: OnceCell<IdIndex>,
     view: View,
 }
@@ -193,7 +192,6 @@ impl ReadonlyRepo {
             settings: repo_settings,
             index_store,
             index: OnceCell::new(),
-            commit_id_index: OnceCell::new(),
             change_id_index: OnceCell::new(),
             view,
         }))
@@ -245,17 +243,6 @@ impl ReadonlyRepo {
         })
     }
 
-    fn commit_id_index(&self) -> &IdIndex {
-        self.commit_id_index.get_or_init(|| {
-            // We need to account for rewritten commits as well
-            let mut id_index = IdIndex::new();
-            for entry in self.as_repo_ref().index().iter() {
-                id_index.insert(entry.commit_id().as_bytes(), ());
-            }
-            id_index
-        })
-    }
-
     fn change_id_index(&self) -> &IdIndex {
         self.change_id_index.get_or_init(|| {
             let all_visible_revisions = crate::revset::RevsetExpression::all()
@@ -278,8 +265,8 @@ impl ReadonlyRepo {
             // The root change/commit ids share the same prefix, and they are found in both
             // indices with different lengths. So we have to feed bytes of valid lengths.
             cmp::max(
-                self.commit_id_index()
-                    .shortest_unique_prefix_len(root_commit_id.as_bytes()),
+                self.index()
+                    .shortest_unique_commit_id_prefix_len(root_commit_id),
                 self.change_id_index()
                     .shortest_unique_prefix_len(root_change_id.as_bytes()),
             )
@@ -289,8 +276,8 @@ impl ReadonlyRepo {
             // `max(len, anything_else)`, so a max of such lengths will disambiguate in all
             // indices.
             cmp::max(
-                self.commit_id_index()
-                    .shortest_unique_prefix_len(target_id_bytes),
+                self.index()
+                    .shortest_unique_commit_id_prefix_len(&CommitId::from_bytes(target_id_bytes)),
                 self.change_id_index()
                     .shortest_unique_prefix_len(target_id_bytes),
             )
@@ -551,7 +538,6 @@ impl RepoLoader {
             settings: self.repo_settings.clone(),
             index_store: self.index_store.clone(),
             index: OnceCell::with_value(index),
-            commit_id_index: OnceCell::new(),
             change_id_index: OnceCell::new(),
             view,
         };
@@ -583,7 +569,6 @@ impl RepoLoader {
             settings: self.repo_settings.clone(),
             index_store: self.index_store.clone(),
             index: OnceCell::new(),
-            commit_id_index: OnceCell::new(),
             change_id_index: OnceCell::new(),
             view,
         };