Make pg_dump exclude unlogged table data on hot standby slaves

Noted by Joe Van Dyk

doc/src/sgml/ref/pg_dump.sgml

@@ -713,7 +713,8 @@ PostgreSQL documentation
        <para>
         Do not dump the contents of unlogged tables.  This option has no
         effect on whether or not the table definitions (schema) are dumped;
-        it only suppresses dumping the table data.
+        it only suppresses dumping the table data. Data in unlogged tables
+        is always excluded when dumping from a standby server.
        </para>
       </listitem>
      </varlistentry>

src/bin/pg_dump/pg_dump.c

@@ -605,6 +605,24 @@ main(int argc, char **argv)
 	if (fout->remoteVersion < 90100)
 		no_security_labels = 1;
 
+	/*
+	 * When running against 9.0 or later, check if we are in recovery mode,
+	 * which means we are on a hot standby.
+	 */
+	if (fout->remoteVersion >= 90000)
+	{
+		PGresult *res = ExecuteSqlQueryForSingleRow(fout, "SELECT pg_catalog.pg_is_in_recovery()");
+		if (strcmp(PQgetvalue(res, 0, 0), "t") == 0)
+		{
+			/*
+			 * On hot standby slaves, never try to dump unlogged table data,
+			 * since it will just throw an error.
+			 */
+			no_unlogged_table_data = true;
+		}
+		PQclear(res);
+	}
+
 	/*
 	 * Start transaction-snapshot mode transaction to dump consistent data.
 	 */