Include more status information in walsender results

Add the current xlog insert location to the response of
IDENTIFY_SYSTEM, and adds result sets containing start
and stop location of backups to BASE_BACKUP responses.

doc/src/sgml/protocol.sgml

@@ -1315,7 +1315,7 @@ The commands accepted in walsender mode are:
     <listitem>
      <para>
       Requests the server to identify itself. Server replies with a result
-      set of a single row, containing two fields:
+      set of a single row, containing three fields:
      </para>
 
      <para>
@@ -1344,6 +1344,19 @@ The commands accepted in walsender mode are:
       </para>
       </listitem>
       </varlistentry>
+
+      <varlistentry>
+      <term>
+       xlogpos
+      </term>
+      <listitem>
+      <para>
+       Current xlog write location. Useful to get a known location in the
+       transaction log where streaming can start.
+      </para>
+      </listitem>
+      </varlistentry>
+
       </variablelist>
      </para>
     </listitem>
@@ -1520,15 +1533,16 @@ The commands accepted in walsender mode are:
       </variablelist>
      </para>
      <para>
-      When the backup is started, the server will first send a header in
-      ordinary result set format, followed by one or more CopyResponse
-      results, one for PGDATA and one for each additional tablespace other
-      than <literal>pg_default</> and <literal>pg_global</>. The data in
-      the CopyResponse results will be a tar format (using ustar00
-      extensions) dump of the tablespace contents.
+      When the backup is started, the server will first send two
+      ordinary result sets, followed by one or more CopyResponse
+      results.
+     </para>
+     <para>
+      The first ordinary result set contains the starting position of the
+      backup, given in XLogRecPtr format as a single column in a single row.
      </para>
      <para>
-      The header is an ordinary resultset with one row for each tablespace.
+      The second ordinary result set has one row for each tablespace.
       The fields in this row are:
       <variablelist>
        <varlistentry>
@@ -1560,6 +1574,15 @@ The commands accepted in walsender mode are:
        </varlistentry>
       </variablelist>
      </para>
+     <para>
+      After the second regular result set, one or more CopyResponse results
+      will be sent, one for PGDATA and one for each additional tablespace other
+      than <literal>pg_default</> and <literal>pg_global</>. The data in
+      the CopyResponse results will be a tar format (using ustar00
+      extensions) dump of the tablespace contents. After the tar data is
+      complete, a final ordinary result set will be sent.
+     </para>
+
      <para>
       The tar archive for the data directory and each tablespace will contain
       all files in the directories, regardless of whether they are
@@ -1583,6 +1606,11 @@ The commands accepted in walsender mode are:
       Owner, group and file mode are set if the underlying filesystem on
       the server supports it.
      </para>
+     <para>
+      Once all tablespaces have been sent, a final regular result set will
+      be sent. This result set contains the end position of the
+      backup, given in XLogRecPtr format as a single column in a single row.
+     </para>
     </listitem>
   </varlistentry>
 </variablelist>

src/backend/replication/basebackup.c

@@ -52,6 +52,7 @@ static void SendBackupHeader(List *tablespaces);
 static void base_backup_cleanup(int code, Datum arg);
 static void perform_base_backup(basebackup_options *opt, DIR *tblspcdir);
 static void parse_basebackup_options(List *options, basebackup_options *opt);
+static void SendXlogRecPtrResult(XLogRecPtr ptr);
 
 /*
  * Size of each block sent into the tar stream for larger files.
@@ -92,6 +93,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 	char	   *labelfile;
 
 	startptr = do_pg_start_backup(opt->label, opt->fastcheckpoint, &labelfile);
+	SendXlogRecPtrResult(startptr);
 
 	PG_ENSURE_ERROR_CLEANUP(base_backup_cleanup, (Datum) 0);
 	{
@@ -239,6 +241,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 		/* Send CopyDone message for the last tar file */
 		pq_putemptymessage('c');
 	}
+	SendXlogRecPtrResult(endptr);
 }
 
 /*
@@ -431,6 +434,42 @@ SendBackupHeader(List *tablespaces)
 	pq_puttextmessage('C', "SELECT");
 }
 
+/*
+ * Send a single resultset containing just a single
+ * XlogRecPtr record (in text format)
+ */
+static void
+SendXlogRecPtrResult(XLogRecPtr ptr)
+{
+	StringInfoData buf;
+	char		str[MAXFNAMELEN];
+
+	snprintf(str, sizeof(str), "%X/%X", ptr.xlogid, ptr.xrecoff);
+
+	pq_beginmessage(&buf, 'T'); /* RowDescription */
+	pq_sendint(&buf, 1, 2);		/* 1 field */
+
+	/* Field header */
+	pq_sendstring(&buf, "recptr");
+	pq_sendint(&buf, 0, 4);		/* table oid */
+	pq_sendint(&buf, 0, 2);		/* attnum */
+	pq_sendint(&buf, TEXTOID, 4);		/* type oid */
+	pq_sendint(&buf, -1, 2);
+	pq_sendint(&buf, 0, 4);
+	pq_sendint(&buf, 0, 2);
+	pq_endmessage(&buf);
+
+	/* Data row */
+	pq_beginmessage(&buf, 'D');
+	pq_sendint(&buf, 1, 2);		/* number of columns */
+	pq_sendint(&buf, strlen(str), 4);	/* length */
+	pq_sendbytes(&buf, str, strlen(str));
+	pq_endmessage(&buf);
+
+	/* Send a CommandComplete message */
+	pq_puttextmessage('C', "SELECT");
+}
+
 /*
  * Inject a file with given name and content in the output tar stream.
  */

src/backend/replication/walsender.c

@@ -258,19 +258,26 @@ IdentifySystem(void)
 	StringInfoData buf;
 	char		sysid[32];
 	char		tli[11];
+	char		xpos[MAXFNAMELEN];
+	XLogRecPtr	logptr;
 
 	/*
-	 * Reply with a result set with one row, two columns. First col is system
-	 * ID, and second is timeline ID
+	 * Reply with a result set with one row, three columns. First col is system
+	 * ID, second is timeline ID, and third is current xlog location.
 	 */
 
 	snprintf(sysid, sizeof(sysid), UINT64_FORMAT,
 			 GetSystemIdentifier());
 	snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);
 
+	logptr = GetInsertRecPtr();
+
+	snprintf(xpos, sizeof(xpos), "%X/%X",
+			 logptr.xlogid, logptr.xrecoff);
+
 	/* Send a RowDescription message */
 	pq_beginmessage(&buf, 'T');
-	pq_sendint(&buf, 2, 2);		/* 2 fields */
+	pq_sendint(&buf, 3, 2);		/* 3 fields */
 
 	/* first field */
 	pq_sendstring(&buf, "systemid");	/* col name */
@@ -289,15 +296,27 @@ IdentifySystem(void)
 	pq_sendint(&buf, 4, 2);		/* typlen */
 	pq_sendint(&buf, 0, 4);		/* typmod */
 	pq_sendint(&buf, 0, 2);		/* format code */
+
+	/* third field */
+	pq_sendstring(&buf, "xlogpos");
+	pq_sendint(&buf, 0, 4);
+	pq_sendint(&buf, 0, 2);
+	pq_sendint(&buf, TEXTOID, 4);
+	pq_sendint(&buf, -1, 2);
+	pq_sendint(&buf, 0, 4);
+	pq_sendint(&buf, 0, 2);
 	pq_endmessage(&buf);
 
 	/* Send a DataRow message */
 	pq_beginmessage(&buf, 'D');
-	pq_sendint(&buf, 2, 2);		/* # of columns */
+	pq_sendint(&buf, 3, 2);		/* # of columns */
 	pq_sendint(&buf, strlen(sysid), 4); /* col1 len */
 	pq_sendbytes(&buf, (char *) &sysid, strlen(sysid));
 	pq_sendint(&buf, strlen(tli), 4);	/* col2 len */
 	pq_sendbytes(&buf, (char *) tli, strlen(tli));
+	pq_sendint(&buf, strlen(xpos), 4);	/* col3 len */
+	pq_sendbytes(&buf, (char *) xpos, strlen(xpos));
+
 	pq_endmessage(&buf);
 
 	/* Send CommandComplete and ReadyForQuery messages */

src/bin/pg_basebackup/pg_basebackup.c

@@ -742,15 +742,40 @@ static void
 BaseBackup()
 {
 	PGresult   *res;
+	uint32		timeline;
 	char		current_path[MAXPGPATH];
 	char		escaped_label[MAXPGPATH];
 	int			i;
+	char		xlogstart[64];
+	char		xlogend[64];
 
 	/*
 	 * Connect in replication mode to the server
 	 */
 	conn = GetConnection();
 
+	/*
+	 * Run IDENFITY_SYSTEM so we can get the timeline
+	 */
+	res = PQexec(conn, "IDENTIFY_SYSTEM");
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		fprintf(stderr, _("%s: could not identify system: %s\n"),
+				progname, PQerrorMessage(conn));
+		disconnect_and_exit(1);
+	}
+	if (PQntuples(res) != 1)
+	{
+		fprintf(stderr, _("%s: could not identify system, got %i rows\n"),
+				progname, PQntuples(res));
+		disconnect_and_exit(1);
+	}
+	timeline = atoi(PQgetvalue(res, 0, 1));
+	PQclear(res);
+
+	/*
+	 * Start the actual backup
+	 */
 	PQescapeStringConn(conn, escaped_label, label, sizeof(escaped_label), &i);
 	snprintf(current_path, sizeof(current_path), "BASE_BACKUP LABEL '%s' %s %s %s",
 			 escaped_label,
@@ -766,7 +791,7 @@ BaseBackup()
 	}
 
 	/*
-	 * Get the header
+	 * Get the starting xlog position
 	 */
 	res = PQgetResult(conn);
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
@@ -775,6 +800,28 @@ BaseBackup()
 				progname, PQerrorMessage(conn));
 		disconnect_and_exit(1);
 	}
+	if (PQntuples(res) != 1)
+	{
+		fprintf(stderr, _("%s: no start point returned from server.\n"),
+				progname);
+		disconnect_and_exit(1);
+	}
+	strcpy(xlogstart, PQgetvalue(res, 0, 0));
+	if (verbose && includewal)
+		fprintf(stderr, "xlog start point: %s\n", xlogstart);
+	PQclear(res);
+	MemSet(xlogend, 0, sizeof(xlogend));
+
+	/*
+	 * Get the header
+	 */
+	res = PQgetResult(conn);
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		fprintf(stderr, _("%s: could not get backup header: %s\n"),
+				progname, PQerrorMessage(conn));
+		disconnect_and_exit(1);
+	}
 	if (PQntuples(res) < 1)
 	{
 		fprintf(stderr, _("%s: no data returned from server.\n"), progname);
@@ -828,6 +875,27 @@ BaseBackup()
 	}
 	PQclear(res);
 
+	/*
+	 * Get the stop position
+	 */
+	res = PQgetResult(conn);
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		fprintf(stderr, _("%s: could not get end xlog position from server.\n"),
+						  progname);
+		disconnect_and_exit(1);
+	}
+	if (PQntuples(res) != 1)
+	{
+		fprintf(stderr, _("%s: no end point returned from server.\n"),
+				progname);
+		disconnect_and_exit(1);
+	}
+	strcpy(xlogend, PQgetvalue(res, 0, 0));
+	if (verbose && includewal)
+		fprintf(stderr, "xlog end point: %s\n", xlogend);
+	PQclear(res);
+
 	res = PQgetResult(conn);
 	if (PQresultStatus(res) != PGRES_COMMAND_OK)
 	{