Rename XLogData protocol message to WALData

This name is only used as documentation, and using this name is
consistent with its byte being a 'w'.  Renaming it would also make the
use of a symbolic name based on the word "WAL" rather than the obsolete
"XLog" term more consistent, per future commits along the lines of
37c7a7eeb6, 4a68d50088, f4b54e1ed9.

Discussion: https://postgr.es/m/aIECfYfevCUpenBT@nathan

doc/src/sgml/protocol.sgml

@@ -2555,8 +2555,8 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
       </para>
 
       <variablelist>
-       <varlistentry id="protocol-replication-xlogdata">
-        <term>XLogData (B)</term>
+       <varlistentry id="protocol-replication-waldata">
+        <term>WALData (B)</term>
         <listitem>
          <variablelist>
           <varlistentry>
@@ -2604,11 +2604,11 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
             </para>
 
             <para>
-             A single WAL record is never split across two XLogData messages.
+             A single WAL record is never split across two WALData messages.
              When a WAL record crosses a WAL page boundary, and is therefore
              already split using continuation records, it can be split at the page
              boundary. In other words, the first main WAL record and its
-             continuation records can be sent in different XLogData messages.
+             continuation records can be sent in different WALData messages.
             </para>
            </listitem>
           </varlistentry>

src/bin/pg_basebackup/pg_recvlogical.c

@@ -517,7 +517,7 @@ StreamLogicalLog(void)
 		}
 
 		/*
-		 * Read the header of the XLogData message, enclosed in the CopyData
+		 * Read the header of the WALData message, enclosed in the CopyData
 		 * message. We only need the WAL location field (dataStart), the rest
 		 * of the header is ignored.
 		 */
@@ -605,7 +605,7 @@ StreamLogicalLog(void)
 		/*
 		 * We're doing a client-initiated clean exit and have sent CopyDone to
 		 * the server. Drain any messages, so we don't miss a last-minute
-		 * ErrorResponse. The walsender stops generating XLogData records once
+		 * ErrorResponse. The walsender stops generating WALData records once
 		 * it sees CopyDone, so expect this to finish quickly. After CopyDone,
 		 * it's too late for sendFeedback(), even if this were to take a long
 		 * time. Hence, use synchronous-mode PQgetCopyData().

src/bin/pg_basebackup/receivelog.c

@@ -38,8 +38,8 @@ static int	CopyStreamReceive(PGconn *conn, long timeout, pgsocket stop_socket,
 							  char **buffer);
 static bool ProcessKeepaliveMsg(PGconn *conn, StreamCtl *stream, char *copybuf,
 								int len, XLogRecPtr blockpos, TimestampTz *last_status);
-static bool ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
-							   XLogRecPtr *blockpos);
+static bool ProcessWALDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
+							  XLogRecPtr *blockpos);
 static PGresult *HandleEndOfCopyStream(PGconn *conn, StreamCtl *stream, char *copybuf,
 									   XLogRecPtr blockpos, XLogRecPtr *stoppos);
 static bool CheckCopyStreamStop(PGconn *conn, StreamCtl *stream, XLogRecPtr blockpos);
@@ -831,7 +831,7 @@ HandleCopyStream(PGconn *conn, StreamCtl *stream,
 			}
 			else if (copybuf[0] == 'w')
 			{
-				if (!ProcessXLogDataMsg(conn, stream, copybuf, r, &blockpos))
+				if (!ProcessWALDataMsg(conn, stream, copybuf, r, &blockpos))
 					goto error;
 
 				/*
@@ -1041,11 +1041,11 @@ ProcessKeepaliveMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
 }
 
 /*
- * Process XLogData message.
+ * Process WALData message.
  */
 static bool
-ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
-				   XLogRecPtr *blockpos)
+ProcessWALDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
+				  XLogRecPtr *blockpos)
 {
 	int			xlogoff;
 	int			bytes_left;
@@ -1054,13 +1054,13 @@ ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
 
 	/*
 	 * Once we've decided we don't want to receive any more, just ignore any
-	 * subsequent XLogData messages.
+	 * subsequent WALData messages.
 	 */
 	if (!(still_sending))
 		return true;
 
 	/*
-	 * Read the header of the XLogData message, enclosed in the CopyData
+	 * Read the header of the WALData message, enclosed in the CopyData
 	 * message. We only need the WAL location field (dataStart), the rest of
 	 * the header is ignored.
 	 */
@@ -1162,7 +1162,7 @@ ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
 					return false;
 				}
 				still_sending = false;
-				return true;	/* ignore the rest of this XLogData packet */
+				return true;	/* ignore the rest of this WALData packet */
 			}
 		}
 	}