diff --git a/lightning/kv/importer.go b/lightning/kv/importer.go
index 6b3377326..460596e8c 100644
--- a/lightning/kv/importer.go
+++ b/lightning/kv/importer.go
@@ -148,8 +148,8 @@ func makeTag(tableName string, engineID int) string {
 
 var engineNamespace = uuid.Must(uuid.FromString("d68d6abe-c59e-45d6-ade8-e2b0ceb7bedf"))
 
-// OpenEngine opens an engine with the given UUID. This type is goroutine safe:
-// you can share this instance and execute any method anywhere.
+// OpenEngine opens an engine with the given table name and engine ID. This type
+// is goroutine safe: you can share this instance and execute any method anywhere.
 func (importer *Importer) OpenEngine(
 	ctx context.Context,
 	tableName string,
diff --git a/tests/checkpoint_engines/config.toml b/tests/checkpoint_engines/config.toml
index e9f041998..190f76280 100644
--- a/tests/checkpoint_engines/config.toml
+++ b/tests/checkpoint_engines/config.toml
@@ -13,7 +13,7 @@ addr = "127.0.0.1:8808"
 
 [mydumper]
 data-source-dir = "tests/checkpoint_engines/data"
-batch-size = 1 # force creating a new batch for every file.
+batch-size = 60 # force splitting the data into 4 batches
 
 [tidb]
 host = "127.0.0.1"
diff --git a/tests/checkpoint_engines/data/cpeng.a.1.sql b/tests/checkpoint_engines/data/cpeng.a.1.sql
index 25d96b2c4..58829b7d8 100644
--- a/tests/checkpoint_engines/data/cpeng.a.1.sql
+++ b/tests/checkpoint_engines/data/cpeng.a.1.sql
@@ -1 +1 @@
-insert into a values (1),(2);
+insert into a values (1);
diff --git a/tests/checkpoint_engines/data/cpeng.a.2.sql b/tests/checkpoint_engines/data/cpeng.a.2.sql
index effdc8f3e..ccbcb5801 100644
--- a/tests/checkpoint_engines/data/cpeng.a.2.sql
+++ b/tests/checkpoint_engines/data/cpeng.a.2.sql
@@ -1 +1 @@
-insert into a values (3),(4);
+insert into a values (2);
diff --git a/tests/checkpoint_engines/data/cpeng.a.3.sql b/tests/checkpoint_engines/data/cpeng.a.3.sql
new file mode 100644
index 000000000..effdc8f3e
--- /dev/null
+++ b/tests/checkpoint_engines/data/cpeng.a.3.sql
@@ -0,0 +1 @@
+insert into a values (3),(4);
diff --git a/tests/checkpoint_engines/data/cpeng.b.1.sql b/tests/checkpoint_engines/data/cpeng.b.1.sql
index 3cee7f262..342c150d9 100644
--- a/tests/checkpoint_engines/data/cpeng.b.1.sql
+++ b/tests/checkpoint_engines/data/cpeng.b.1.sql
@@ -1 +1,4 @@
 insert into b values (10),(11),(12);
+/*
+padding to make the data file > 50 bytes
+*/
\ No newline at end of file
diff --git a/tests/checkpoint_engines/mysql.toml b/tests/checkpoint_engines/mysql.toml
index 5947da587..ff00fad82 100644
--- a/tests/checkpoint_engines/mysql.toml
+++ b/tests/checkpoint_engines/mysql.toml
@@ -13,7 +13,7 @@ addr = "127.0.0.1:8808"
 
 [mydumper]
 data-source-dir = "tests/checkpoint_engines/data"
-batch-size = 1 # force creating a new batch for every file.
+batch-size = 50 # force splitting the data into 4 batches
 
 [tidb]
 host = "127.0.0.1"