diff --git a/components/cdc/src/service.rs b/components/cdc/src/service.rs
index 53f471c1939..2ce8f2c218e 100644
--- a/components/cdc/src/service.rs
+++ b/components/cdc/src/service.rs
@@ -59,11 +59,11 @@ impl CdcEvent {
                 // See https://play.golang.org/p/GFA9S-z_kUt
                 let approximate_region_id_bytes = 4;
                 let approximate_tso_bytes = 9;
-                // Protobuf encoding adds a tag to every varints.
+                // Protobuf encoding adds a tag to every Uvarint.
                 // protobuf::rt::tag_size(1 /* or 2, field number*/) yields 1.
                 let tag_bytes = 1;
 
-                // Byets of an array of region id.
+                // Bytes of an array of region id.
                 r.regions.len() as u32 * (tag_bytes + approximate_region_id_bytes)
                 // Bytes of a TSO.
                 + (tag_bytes + approximate_tso_bytes)
diff --git a/components/cdc/tests/integrations/test_cdc.rs b/components/cdc/tests/integrations/test_cdc.rs
index fa9c5f2d748..d2aa2f70c82 100644
--- a/components/cdc/tests/integrations/test_cdc.rs
+++ b/components/cdc/tests/integrations/test_cdc.rs
@@ -171,7 +171,7 @@ fn test_cdc_basic() {
     let mut req = suite.new_changedata_request(1);
     req.set_region_epoch(Default::default()); // Zero region epoch.
     let (mut req_tx, resp_rx) = suite.get_region_cdc_client(1).event_feed().unwrap();
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     event_feed_wrap.replace(Some(resp_rx));
     let mut events = receive_event(false).events.to_vec();
     assert_eq!(events.len(), 1);
@@ -277,7 +277,7 @@ fn test_cdc_not_leader() {
     rx.recv_timeout(Duration::from_millis(200)).unwrap();
 
     // Try to subscribe again.
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     let mut events = receive_event(false).events.to_vec();
     assert_eq!(events.len(), 1);
     // Should failed with not leader error.
@@ -485,7 +485,7 @@ fn test_cdc_scan() {
     req.checkpoint_ts = checkpoint_ts.into_inner();
     let (mut req_tx, resp_rx) = suite.get_region_cdc_client(1).event_feed().unwrap();
     event_feed_wrap.replace(Some(resp_rx));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     let mut events = receive_event(false).events.to_vec();
     if events.len() == 1 {
         events.extend(receive_event(false).events.to_vec());
@@ -687,7 +687,7 @@ fn test_duplicate_subscribe() {
         other => panic!("unknown event {:?}", other),
     }
     // Try to subscribe again.
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     let mut events = receive_event(false).events.to_vec();
     assert_eq!(events.len(), 1);
     // Should receive duplicate request error.
@@ -800,7 +800,7 @@ fn test_old_value_basic() {
     req.set_extra_op(ExtraOp::ReadOldValue);
     let (mut req_tx, event_feed_wrap, receive_event) =
         new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx = block_on(req_tx.send((req.clone(), WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req.clone(), WriteFlags::default()))).unwrap();
     sleep_ms(1000);
 
     // Insert value
@@ -912,7 +912,7 @@ fn test_old_value_basic() {
 
     let (mut req_tx, resp_rx) = suite.get_region_cdc_client(1).event_feed().unwrap();
     event_feed_wrap.replace(Some(resp_rx));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     let mut event_count = 0;
     loop {
         let event = receive_event(false);
@@ -957,12 +957,12 @@ fn test_old_value_multi_changefeeds() {
     req.set_extra_op(ExtraOp::ReadOldValue);
     let (mut req_tx_1, event_feed_wrap_1, receive_event_1) =
         new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx_1 = block_on(req_tx_1.send((req.clone(), WriteFlags::default()))).unwrap();
+    block_on(req_tx_1.send((req.clone(), WriteFlags::default()))).unwrap();
 
     req.set_extra_op(ExtraOp::Noop);
     let (mut req_tx_2, event_feed_wrap_2, receive_event_2) =
         new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx_2 = block_on(req_tx_2.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx_2.send((req, WriteFlags::default()))).unwrap();
 
     sleep_ms(1000);
     // Insert value
@@ -1065,7 +1065,7 @@ fn test_cdc_resolve_ts_checking_concurrency_manager() {
     req.set_checkpoint_ts(100);
     let (mut req_tx, event_feed_wrap, receive_event) =
         new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     // Make sure region 1 is registered.
     let mut events = receive_event(false).events;
     assert_eq!(events.len(), 1);
@@ -1222,7 +1222,7 @@ fn test_old_value_1pc() {
     let mut req = suite.new_changedata_request(1);
     req.set_extra_op(ExtraOp::ReadOldValue);
     let (mut req_tx, _, receive_event) = new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
 
     // Insert value
     let mut m1 = Mutation::default();
@@ -1283,7 +1283,7 @@ fn test_old_value_cache_hit() {
     req.set_extra_op(ExtraOp::ReadOldValue);
     let (mut req_tx, event_feed_wrap, receive_event) =
         new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     let mut events = receive_event(false).events.to_vec();
     match events.remove(0).event.unwrap() {
         Event_oneof_event::Entries(mut es) => {
@@ -1432,7 +1432,7 @@ fn test_old_value_cache_hit_pessimistic() {
     req.set_extra_op(ExtraOp::ReadOldValue);
     let (mut req_tx, event_feed_wrap, receive_event) =
         new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
     let mut events = receive_event(false).events.to_vec();
     match events.remove(0).event.unwrap() {
         Event_oneof_event::Entries(mut es) => {
@@ -1942,7 +1942,7 @@ fn test_cdc_no_write_corresponding_to_lock() {
     let mut req = suite.new_changedata_request(1);
     req.set_extra_op(ExtraOp::ReadOldValue);
     let (mut req_tx, _, receive_event) = new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
 
     // Txn1 commit_ts = 15
     let mut m1 = Mutation::default();
@@ -1987,7 +1987,7 @@ fn test_cdc_write_rollback_when_no_lock() {
     let mut req = suite.new_changedata_request(1);
     req.set_extra_op(ExtraOp::ReadOldValue);
     let (mut req_tx, _, receive_event) = new_event_feed(suite.get_region_cdc_client(1));
-    let _req_tx = block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
+    block_on(req_tx.send((req, WriteFlags::default()))).unwrap();
 
     // Txn1 commit_ts = 15
     let mut m1 = Mutation::default();