fix a flaky test in boltdb shipper (#2550)

pkg/storage/stores/shipper/uploads/table.go

@@ -198,9 +198,7 @@ func (lt *Table) Upload(ctx context.Context, force bool) error {
 	lt.dbsMtx.RLock()
 	defer lt.dbsMtx.RUnlock()
 
-	// upload files excluding active shard. It could so happen that we just started a new shard but the file for last shard is still being updated due to pending writes or pending flush to disk.
-	// To avoid uploading it, excluding previous active shard as well if it has been not more than a minute since it became inactive.
-	uploadShardsBefore := fmt.Sprint(time.Now().Add(-time.Minute).Truncate(shardDBsByDuration).Unix())
+	uploadShardsBefore := fmt.Sprint(getOldestActiveShardTime().Unix())
 
 	// Adding check for considering only files which are sharded and have just an epoch in their name.
 	// Before introducing sharding we had a single file per table which were were moved inside the folder per table as part of migration.
@@ -379,3 +377,10 @@ func loadBoltDBsFromDir(dir string) (map[string]*bbolt.DB, error) {
 
 	return dbs, nil
 }
+
+// getOldestActiveShardTime returns the time of oldest active shard with a buffer of 1 minute.
+func getOldestActiveShardTime() time.Time {
+	// upload files excluding active shard. It could so happen that we just started a new shard but the file for last shard is still being updated due to pending writes or pending flush to disk.
+	// To avoid uploading it, excluding previous active shard as well if it has been not more than a minute since it became inactive.
+	return time.Now().Add(-time.Minute).Truncate(shardDBsByDuration)
+}

pkg/storage/stores/shipper/uploads/table_test.go

@@ -378,13 +378,14 @@ func TestTable_ImmutableUploads(t *testing.T) {
 		boltDBIndexClient.Stop()
 	}()
 
-	activeShard := time.Now().Truncate(shardDBsByDuration)
+	// shardCutoff is calulated based on when shards are considered to not be active anymore and are safe to be uploaded.
+	shardCutoff := getOldestActiveShardTime()
 
 	// some dbs to setup
 	dbNames := []int64{
-		activeShard.Add(-shardDBsByDuration).Unix(), // inactive shard, should upload
-		activeShard.Add(-2 * time.Minute).Unix(),    // 2 minutes before active shard, should upload
-		activeShard.Unix(),                          // active shard, should not upload
+		shardCutoff.Add(-shardDBsByDuration).Unix(),    // inactive shard, should upload
+		shardCutoff.Add(-1 * time.Minute).Unix(),       // 1 minute before shard cutoff, should upload
+		time.Now().Truncate(shardDBsByDuration).Unix(), // active shard, should not upload
 	}
 
 	dbs := map[string]testutil.DBRecords{}