Add new actionrunner.stream_output_buf_size config option and use that

value for "bufsize" argument inside the Python runner run_command
function call.

For performance reasons, default it to -1, but allow users to change it
via config if they are experiencing performance or similar issues.

contrib/runners/python_runner/python_runner/python_runner.py

@@ -248,8 +248,11 @@ def run(self, action_parameters):
         if stdin_params:
             command_string = 'echo %s | %s' % (quote_unix(stdin_params), command_string)
 
-        LOG.debug('Running command: PATH=%s PYTHONPATH=%s %s' % (env['PATH'], env['PYTHONPATH'],
-                                                                 command_string))
+        bufsize = cfg.CONF.actionrunner.stream_output_buffer_size
+
+        LOG.debug('Running command (bufsize=%s): PATH=%s PYTHONPATH=%s %s' % (bufsize, env['PATH'],
+                                                                              env['PYTHONPATH'],
+                                                                              command_string))
         exit_code, stdout, stderr, timed_out = run_command(cmd=args,
                                                            stdin=stdin,
                                                            stdout=subprocess.PIPE,
@@ -261,7 +264,8 @@ def run(self, action_parameters):
                                                            read_stderr_func=read_and_store_stderr,
                                                            read_stdout_buffer=stdout,
                                                            read_stderr_buffer=stderr,
-                                                           stdin_value=stdin_params)
+                                                           stdin_value=stdin_params,
+                                                           bufsize=bufsize)
         LOG.debug('Returning values: %s, %s, %s, %s', exit_code, stdout, stderr, timed_out)
         LOG.debug('Returning.')
         return self._get_output_values(exit_code, stdout, stderr, timed_out)

st2common/st2common/config.py

@@ -376,7 +376,13 @@ def register_opts(ignore_errors=False):
                  'creates pack virtualenv.'),
         cfg.BoolOpt(
             'stream_output', default=True,
-            help='True to store and stream action output (stdout and stderr) in real-time.')
+            help='True to store and stream action output (stdout and stderr) in real-time.'),
+        cfg.IntOpt(
+            'stream_output_buffer_size', default=-1,
+            help=('Buffer size to use for real time action output streaming. 0 means unbuffered '
+                  '1 means line buffered, -1 means system default, which usually means fully '
+                  'buffered and any other positive value means use a buffer of (approximately) '
+                  'that size'))
     ]
 
     do_register_opts(action_runner_opts, group='actionrunner')