From 9b57cb17e6695b00d9f93ff61b10d9a87c2ab8d5 Mon Sep 17 00:00:00 2001
From: Fraser Savage <fsavage@influxdata.com>
Date: Fri, 1 Sep 2023 16:35:42 +0100
Subject: [PATCH] test(ingester): Cover WAL replay of empty files

Clearing out the TODO
---
 ingester/src/init/wal_replay.rs | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/ingester/src/init/wal_replay.rs b/ingester/src/init/wal_replay.rs
index 5ae06447f5..11029feb27 100644
--- a/ingester/src/init/wal_replay.rs
+++ b/ingester/src/init/wal_replay.rs
@@ -124,9 +124,7 @@ where
                     "dropping empty wal segment",
                 );
 
-                // TODO(test): empty WAL replay
-
-                // A failure to delete an empty file should not prevent WAL
+                // A failure to delete an empty file MUST not prevent WAL
                 // replay from continuing.
                 if let Err(error) = wal.delete(file.id()).await {
                     error!(
@@ -381,7 +379,8 @@ mod tests {
 
         // The write portion of this test.
         //
-        // Write two ops, rotate the file, and write a third op.
+        // Write two ops, rotate the file twice (ensuring an empty file is
+        // handled ok), write a third op and finally an empty op.
         {
             let inner = Arc::new(MockDmlSink::default().with_apply_return(vec![
                 Ok(()),
@@ -414,6 +413,10 @@ mod tests {
             // Rotate the log file
             wal.rotate().expect("failed to rotate WAL file");
 
+            // Rotate the log file again, in order to create an empty segment and ensure
+            // replay is tolerant to it
+            wal.rotate().expect("failed to rotate WAL file");
+
             // Write the third op
             wal_sink
                 .apply(IngestOp::Write(op3.clone()))
@@ -435,7 +438,8 @@ mod tests {
             .await
             .expect("failed to initialise WAL");
 
-        assert_eq!(wal.closed_segments().len(), 2);
+        // Must be 3 segments, 1 OK, 1 Empty and 1 with a normal op and blank op
+        assert_eq!(wal.closed_segments().len(), 3);
 
         // Initialise the mock persist system
         let persist = Arc::new(MockPersistQueue::default());
@@ -497,7 +501,7 @@ mod tests {
             .join()
             .await;
 
-        // Ensure the replayed segments were dropped
+        // Ensure the replayed segments were dropped, including the empty one
         let wal = Wal::new(dir.path())
             .await
             .expect("failed to initialise WAL");
@@ -511,7 +515,7 @@ mod tests {
             .get_observer(&Attributes::from([]))
             .expect("attributes not found")
             .fetch();
-        assert_eq!(files, 2);
+        assert_eq!(files, 3);
         let ops = metrics
             .get_instrument::<Metric<U64Counter>>("ingester_wal_replay_ops")
             .expect("file counter not found")