diff --git a/src/backend/replication/logical/applyparallelworker.c b/src/backend/replication/logical/applyparallelworker.c
index 3acf9d5fb9..1fc62cdba2 100644
--- a/src/backend/replication/logical/applyparallelworker.c
+++ b/src/backend/replication/logical/applyparallelworker.c
@@ -74,10 +74,10 @@
  * messages, and this wait doesn't appear in lmgr.
  *
  * To resolve this issue, we use non-blocking write and wait with a timeout. If
- * timeout is exceeded, the LA will serialize the message to a file and
+ * the timeout is exceeded, the LA will serialize the message to a file and
  * indicate PA-2 that it needs to read that file for the remaining messages.
  * Then LA will start waiting for commit which will detect deadlock if any.
- * (See pa_send_data() and typedef enum TransApplyAction)
+ * (See pa_send_data() and enum TransApplyAction)
  *
  * 4) Lock type
  *
@@ -1147,9 +1147,10 @@ pa_send_data(ParallelApplyWorkerInfo *winfo, Size nbytes, const void *data)
 			LogicalRepMsgType action;
 
 			/*
-			 * The parallel apply worker might be stuck for some reason, so
-			 * stop sending data directly to it and start to serialize data to
-			 * files instead.
+			 * The parallel apply worker could be stuck for some reason (say
+			 * waiting on some lock by other backend), so stop trying to send
+			 * data directly to it and instead start to serialize data to
+			 * file instead.
 			 */
 			winfo->serialize_changes = true;
 
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5fb74572e..c51d92b67f 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -1331,7 +1331,6 @@ apply_handle_stream_prepare(StringInfo s)
 			 */
 			pa_unlock_stream(winfo->shared->xid, AccessExclusiveLock);
 
-			/* Send STREAM PREPARE message to the parallel apply worker. */
 			if (apply_action == TRANS_LEADER_SEND_TO_PARALLEL)
 				pa_send_data(winfo, s->len, s->data);
 			else
@@ -1339,6 +1338,10 @@ apply_handle_stream_prepare(StringInfo s)
 											 LOGICAL_REP_MSG_STREAM_PREPARE,
 											 &original_msg);
 
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
 			if (winfo->serialize_changes)
 				pa_set_fileset_state(winfo->shared, FS_READY);
 
@@ -1840,6 +1843,10 @@ apply_handle_stream_abort(StringInfo s)
 
 			if (toplevel_xact)
 			{
+				/*
+				 * It is possible that while sending this change to parallel apply
+				 * worker we need to switch to serialize mode.
+				 */
 				if (winfo->serialize_changes)
 					pa_set_fileset_state(winfo->shared,
 										 FS_READY);
@@ -2062,13 +2069,16 @@ apply_handle_stream_commit(StringInfo s)
 			 */
 			pa_unlock_stream(xid, AccessExclusiveLock);
 
-			/* Send STREAM COMMIT message to the parallel apply worker. */
 			if (apply_action == TRANS_LEADER_SEND_TO_PARALLEL)
 				pa_send_data(winfo, s->len, s->data);
 			else
 				stream_open_and_write_change(xid, LOGICAL_REP_MSG_STREAM_COMMIT,
 											 &original_msg);
 
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
 			if (winfo->serialize_changes)
 				pa_set_fileset_state(winfo->shared,
 									 FS_READY);