changes_amit_1.patch

diff --git a/src/backend/replication/logical/applyparallelworker.c b/src/backend/replication/logical/applyparallelworker.c
index 7422521626..7a30828d44 100644
--- a/src/backend/replication/logical/applyparallelworker.c
+++ b/src/backend/replication/logical/applyparallelworker.c
@@ -138,10 +138,11 @@
  * wait to send messages, and this wait doesn't appear in lmgr.
  *
  * To avoid this wait, we use a non-blocking write and wait with a timeout. If
- * 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 enum TransApplyAction.
+ * the timeout is exceeded, the LA will serialize all the pending messages 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 as in the previous case
+ * which will detect deadlock if any. See pa_send_data() and
+ * enum TransApplyAction.
  *
  * 4) Lock types
  *
@@ -575,11 +576,13 @@ pa_free_worker(ParallelApplyWorkerInfo *winfo)
 	/*
 	 * Stop the worker if there are enough workers in the pool.
 	 *
-	 * XXX The worker is also stopped if the leader apply worker needed to
+	 * XXX Additionally, we also stop the worker if the leader apply worker
 	 * serialize part of the transaction data due to a send timeout. This is
-	 * because the message could be partially written to the queue but there is
+	 * because the message could be partially written to the queue and there is
 	 * no way to clean the queue other than resending the message until it
-	 * succeeds. Directly stopping the worker avoids needing this complexity.
+	 * succeeds. Instead of trying to send the data which anyway would have
+	 * been serialized and then letting the parallel apply worker deal with the
+	 * spurious message, we stop the worker.
 	 */
 	if (winfo->serialize_changes ||
 		list_length(ParallelApplyWorkerPool) >
@@ -652,7 +655,7 @@ pa_detach_all_error_mq(void)
 }
 
 /*
- * Check if the parallel apply worker is pending due to spooled messages.
+ * Check if there are any pending spooled messages.
  */
 static bool
 pa_has_spooled_message_pending()
@@ -665,8 +668,8 @@ pa_has_spooled_message_pending()
 }
 
 /*
- * Replay the spooled messages in the parallel apply worker if the leader apply
- * worker has finished serializing changes to the file.
+ * Replay the spooled messages once the leader apply worker has finished
+ * serializing changes to the file.
  */
 static void
 pa_spooled_messages(void)
@@ -699,8 +702,8 @@ pa_spooled_messages(void)
 	 * We cannot read the file immediately after the leader has serialized all
 	 * changes to the file because there may still be messages in the memory
 	 * queue. We will apply all spooled messages the next time we call this
-	 * function, which should ensure that there are no messages left in the
-	 * memory queue.
+	 * function and that will ensure there are no messages left in the memory
+	 * queue.
 	 */
 	else if (fileset_state == FS_SERIALIZE_DONE)
 	{
@@ -811,7 +814,7 @@ LogicalParallelApplyLoop(shm_mq_handle *mqh)
 		}
 		else if (shmq_res == SHM_MQ_WOULD_BLOCK)
 		{
-			/* Check if changes have been serialized to a file. */
+			/* Replay the changes from the file, if any. */
 			if (pa_has_spooled_message_pending())
 			{
 				pa_spooled_messages();
@@ -1207,8 +1210,7 @@ pa_send_data(ParallelApplyWorkerInfo *winfo, Size nbytes, const void *data)
  * Switch to PARTIAL_SERIALIZE mode for the current transaction -- this means
  * that the current data and any subsequent data for this transaction will be
  * serialized to a file. This is done to prevent possible deadlocks with
- * another parallel apply worker (refer to the comments atop
- * applyparallelworker.c for details).
+ * another parallel apply worker (refer to the comments atop this file).
  */
 void
 pa_switch_to_partial_serialize(ParallelApplyWorkerInfo *winfo,
@@ -1217,7 +1219,7 @@ pa_switch_to_partial_serialize(ParallelApplyWorkerInfo *winfo,
 	/*
 	 * 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 start to serialize data to file instead.
+	 * and start serializing data to the file instead.
 	 */
 	winfo->serialize_changes = true;
 
@@ -1488,7 +1490,7 @@ pa_stream_abort(LogicalRepStreamAbortData *abort_data)
 }
 
 /*
- * Set the fileset state for the given parallel apply worker. The fileset
+ * Set the fileset state for a particular parallel apply worker. The fileset
  * will be set once the leader worker serialized all changes to the file
  * so that it can be used by parallel apply worker.
  */