Refactor to make common functions in proto.c and worker.c.

This is a non-functional change only to refactor code to extract some
replication logic into static functions.

This is done as preparation for the 2PC streaming patch which also shares
this common logic.

Author: Peter Smith
Reviewed-By: Amit Kapila
Discussion: https://postgr.es/m/CAHut+PuiSA8AiLcE2N5StzSKs46SQEP_vDOUD5fX2XCVtfZ7mQ@mail.gmail.com

Author: Amit Kapila

src/backend/replication/logical/proto.c

@@ -145,22 +145,23 @@ logicalrep_read_begin_prepare(StringInfo in, LogicalRepPreparedTxnData *begin_da
 }
 
 /*
- * Write PREPARE to the output stream.
+ * The core functionality for logicalrep_write_prepare.
  */
-void
-logicalrep_write_prepare(StringInfo out, ReorderBufferTXN *txn,
-						 XLogRecPtr prepare_lsn)
+static void
+logicalrep_write_prepare_common(StringInfo out, LogicalRepMsgType type,
+								ReorderBufferTXN *txn, XLogRecPtr prepare_lsn)
 {
 	uint8		flags = 0;
 
-	pq_sendbyte(out, LOGICAL_REP_MSG_PREPARE);
+	pq_sendbyte(out, type);
 
 	/*
 	 * This should only ever happen for two-phase commit transactions, in
 	 * which case we expect to have a valid GID.
 	 */
 	Assert(txn->gid != NULL);
 	Assert(rbtxn_prepared(txn));
+	Assert(TransactionIdIsValid(txn->xid));
 
 	/* send the flags field */
 	pq_sendbyte(out, flags);
@@ -176,31 +177,52 @@ logicalrep_write_prepare(StringInfo out, ReorderBufferTXN *txn,
 }
 
 /*
- * Read transaction PREPARE from the stream.
+ * Write PREPARE to the output stream.
  */
 void
-logicalrep_read_prepare(StringInfo in, LogicalRepPreparedTxnData *prepare_data)
+logicalrep_write_prepare(StringInfo out, ReorderBufferTXN *txn,
+						 XLogRecPtr prepare_lsn)
+{
+	logicalrep_write_prepare_common(out, LOGICAL_REP_MSG_PREPARE,
+									txn, prepare_lsn);
+}
+
+/*
+ * The core functionality for logicalrep_read_prepare.
+ */
+static void
+logicalrep_read_prepare_common(StringInfo in, char *msgtype,
+							   LogicalRepPreparedTxnData *prepare_data)
 {
 	/* read flags */
 	uint8		flags = pq_getmsgbyte(in);
 
 	if (flags != 0)
-		elog(ERROR, "unrecognized flags %u in prepare message", flags);
+		elog(ERROR, "unrecognized flags %u in %s message", flags, msgtype);
 
 	/* read fields */
 	prepare_data->prepare_lsn = pq_getmsgint64(in);
 	if (prepare_data->prepare_lsn == InvalidXLogRecPtr)
-		elog(ERROR, "prepare_lsn is not set in prepare message");
+		elog(ERROR, "prepare_lsn is not set in %s message", msgtype);
 	prepare_data->end_lsn = pq_getmsgint64(in);
 	if (prepare_data->end_lsn == InvalidXLogRecPtr)
-		elog(ERROR, "end_lsn is not set in prepare message");
+		elog(ERROR, "end_lsn is not set in %s message", msgtype);
 	prepare_data->prepare_time = pq_getmsgint64(in);
 	prepare_data->xid = pq_getmsgint(in, 4);
 
 	/* read gid (copy it into a pre-allocated buffer) */
 	strlcpy(prepare_data->gid, pq_getmsgstring(in), sizeof(prepare_data->gid));
 }
 
+/*
+ * Read transaction PREPARE from the stream.
+ */
+void
+logicalrep_read_prepare(StringInfo in, LogicalRepPreparedTxnData *prepare_data)
+{
+	logicalrep_read_prepare_common(in, "prepare", prepare_data);
+}
+
 /*
  * Write COMMIT PREPARED to the output stream.
  */

src/backend/replication/logical/worker.c

@@ -333,6 +333,8 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 /* Compute GID for two_phase transactions */
 static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
+/* Common streaming function to apply all the spooled messages */
+static void apply_spooled_messages(TransactionId xid, XLogRecPtr lsn);
 
 /*
  * Should this worker apply changes for given relation.
@@ -884,14 +886,47 @@ apply_handle_begin_prepare(StringInfo s)
 	pgstat_report_activity(STATE_RUNNING, NULL);
 }
 
+/*
+ * Common function to prepare the GID.
+ */
+static void
+apply_handle_prepare_internal(LogicalRepPreparedTxnData *prepare_data)
+{
+	char		gid[GIDSIZE];
+
+	/*
+	 * Compute unique GID for two_phase transactions. We don't use GID of
+	 * prepared transaction sent by server as that can lead to deadlock when
+	 * we have multiple subscriptions from same node point to publications on
+	 * the same node. See comments atop worker.c
+	 */
+	TwoPhaseTransactionGid(MySubscription->oid, prepare_data->xid,
+						   gid, sizeof(gid));
+
+	/*
+	 * BeginTransactionBlock is necessary to balance the EndTransactionBlock
+	 * called within the PrepareTransactionBlock below.
+	 */
+	BeginTransactionBlock();
+	CommitTransactionCommand(); /* Completes the preceding Begin command. */
+
+	/*
+	 * Update origin state so we can restart streaming from correct position
+	 * in case of crash.
+	 */
+	replorigin_session_origin_lsn = prepare_data->end_lsn;
+	replorigin_session_origin_timestamp = prepare_data->prepare_time;
+
+	PrepareTransactionBlock(gid);
+}
+
 /*
  * Handle PREPARE message.
  */
 static void
 apply_handle_prepare(StringInfo s)
 {
 	LogicalRepPreparedTxnData prepare_data;
-	char		gid[GIDSIZE];
 
 	logicalrep_read_prepare(s, &prepare_data);
 
@@ -902,15 +937,6 @@ apply_handle_prepare(StringInfo s)
 								 LSN_FORMAT_ARGS(prepare_data.prepare_lsn),
 								 LSN_FORMAT_ARGS(remote_final_lsn))));
 
-	/*
-	 * Compute unique GID for two_phase transactions. We don't use GID of
-	 * prepared transaction sent by server as that can lead to deadlock when
-	 * we have multiple subscriptions from same node point to publications on
-	 * the same node. See comments atop worker.c
-	 */
-	TwoPhaseTransactionGid(MySubscription->oid, prepare_data.xid,
-						   gid, sizeof(gid));
-
 	/*
 	 * Unlike commit, here, we always prepare the transaction even though no
 	 * change has happened in this transaction. It is done this way because at
@@ -923,21 +949,8 @@ apply_handle_prepare(StringInfo s)
 	 */
 	begin_replication_step();
 
-	/*
-	 * BeginTransactionBlock is necessary to balance the EndTransactionBlock
-	 * called within the PrepareTransactionBlock below.
-	 */
-	BeginTransactionBlock();
-	CommitTransactionCommand(); /* Completes the preceding Begin command. */
-
-	/*
-	 * Update origin state so we can restart streaming from correct position
-	 * in case of crash.
-	 */
-	replorigin_session_origin_lsn = prepare_data.end_lsn;
-	replorigin_session_origin_timestamp = prepare_data.prepare_time;
+	apply_handle_prepare_internal(&prepare_data);
 
-	PrepareTransactionBlock(gid);
 	end_replication_step();
 	CommitTransactionCommand();
 	pgstat_report_stat(false);
@@ -1256,30 +1269,19 @@ apply_handle_stream_abort(StringInfo s)
 }
 
 /*
- * Handle STREAM COMMIT message.
+ * Common spoolfile processing.
  */
 static void
-apply_handle_stream_commit(StringInfo s)
+apply_spooled_messages(TransactionId xid, XLogRecPtr lsn)
 {
-	TransactionId xid;
 	StringInfoData s2;
 	int			nchanges;
 	char		path[MAXPGPATH];
 	char	   *buffer = NULL;
-	LogicalRepCommitData commit_data;
 	StreamXidHash *ent;
 	MemoryContext oldcxt;
 	BufFile    *fd;
 
-	if (in_streamed_transaction)
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("STREAM COMMIT message without STREAM STOP")));
-
-	xid = logicalrep_read_stream_commit(s, &commit_data);
-
-	elog(DEBUG1, "received commit for streamed transaction %u", xid);
-
 	/* Make sure we have an open transaction */
 	begin_replication_step();
 
@@ -1311,7 +1313,7 @@ apply_handle_stream_commit(StringInfo s)
 
 	MemoryContextSwitchTo(oldcxt);
 
-	remote_final_lsn = commit_data.commit_lsn;
+	remote_final_lsn = lsn;
 
 	/*
 	 * Make sure the handle apply_dispatch methods are aware we're in a remote
@@ -1390,6 +1392,29 @@ apply_handle_stream_commit(StringInfo s)
 	elog(DEBUG1, "replayed %d (all) changes from file \"%s\"",
 		 nchanges, path);
 
+	return;
+}
+
+/*
+ * Handle STREAM COMMIT message.
+ */
+static void
+apply_handle_stream_commit(StringInfo s)
+{
+	TransactionId xid;
+	LogicalRepCommitData commit_data;
+
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM COMMIT message without STREAM STOP")));
+
+	xid = logicalrep_read_stream_commit(s, &commit_data);
+
+	elog(DEBUG1, "received commit for streamed transaction %u", xid);
+
+	apply_spooled_messages(xid, commit_data.commit_lsn);
+
 	apply_handle_commit_internal(s, &commit_data);
 
 	/* unlink the files with serialized changes and subxact info */