cache heads

To reduce the number of write locks, heads are now cached.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/swarm/relay.rs b/src/swarm/relay.rs
index 454a46a..492b59d 100644
--- a/src/swarm/relay.rs
+++ b/src/swarm/relay.rs
@@ -52,6 +52,10 @@ pub(crate) async fn pull_if_behind(state: &AppState, peer: &str, remote: &transp
     if remote.epoch != state.local_epoch() || !topology::is_neighbour(state, peer) {
         return;
     }
+    // The common case, the same heads, needs only the cached heads (read lock).
+    if HeadsSummary::of(state.doc.read().await.heads().to_vec()) == remote.heads {
+        return;
+    }
     let missing = match &remote.heads {
         HeadsSummary::Heads(heads) => {
             // AutoCommit's lookups take &mut self.