fix catch-up / compaction in general

1 files changed, 9 insertions, 2 deletions

diff --git a/src/compaction/switch.rs b/src/compaction/switch.rs
index 9f17df2..4093e7d 100644
--- a/src/compaction/switch.rs
+++ b/src/compaction/switch.rs
@@ -141,6 +141,11 @@ async fn switch<H: Host>(host: &H, id: &str, record: &Record) -> Result<ReplaySt
     let previous = request.previous;
     let base = request.base_heads.clone();
     let retention = record.proposal.policy.archive_retention.clone();
+    // Only the coordinator carries the record into the new epoch: one writer, so the
+    // nodes don't all write the same path concurrently right after switching (a merge
+    // conflict, plus one change per node to sync). The epoch metadata in the snapshot
+    // keeps the essentials on every node anyway.
+    let carry_record = record.proposal.coordinator == host.node_id();
     let record_path = records::record_path(id, "");
 
     info!(compaction = %id, from = %previous, to = %expected, "Switching epoch");
@@ -172,8 +177,10 @@ async fn switch<H: Host>(host: &H, id: &str, record: &Record) -> Result<ReplaySt
             let mut doc = snapshot.doc.with_actor(ActorId::random());
 
             // Keep this compaction's record visible in the new epoch, for its history.
-            if let Err(error) = store::copy_path(&copy, &mut doc, &record_path) {
-                warn!(error = %error, "Could not carry the compaction record into the new epoch");
+            if carry_record {
+                if let Err(error) = store::copy_path(&copy, &mut doc, &record_path) {
+                    warn!(error = %error, "Could not carry the compaction record into the new epoch");
+                }
             }
 
             let heads = copy.get_heads();