predict: don't auto-load stats if not needed

and make docs conform to the reality.

modules/predict/README.rst

@@ -15,8 +15,6 @@ ahead of time. This is helpful to minimize the perceived latency and keeps the c
 Example configuration
 ^^^^^^^^^^^^^^^^^^^^^
 
-.. warning:: This module requires 'stats' module to be present and loaded.
-
 .. code-block:: lua
 
 	modules = {
@@ -29,7 +27,9 @@ Example configuration
 Defaults are 15 minutes window, 6 hours period.
 
 .. tip:: Use period 0 to turn off prediction and just do prefetching of expiring records.
-    That works even without the 'stats' module.
+    That works even without the :ref:`stats <mod-stats>` module.
+
+.. note:: Otherwise this module requires :ref:`stats <mod-stats>` module and loads it if not present.
 
 Exported metrics
 ^^^^^^^^^^^^^^^^
@@ -45,7 +45,7 @@ Properties
 ^^^^^^^^^^
 
 .. function:: predict.config({ window = 15, period = 24})
-  
+
   Reconfigure the predictor to given tracking window and period length. Both parameters are optional.
   Window length is in minutes, period is a number of windows that can be kept in memory.
   e.g. if a ``window`` is 15 minutes, a ``period`` of "24" means 6 hours.

modules/predict/predict.lua

@@ -13,8 +13,6 @@ local predict = {
 	log = {},
 }
 
--- Load dependent modules
-if not stats then modules.load('stats') end
 
 -- Calculate next sample with jitter [1-2/5 of window]
 local function next_event()
@@ -163,6 +161,8 @@ function predict.config(config)
 	if type(config) ~= 'table' then return end
 	if config.window then predict.window = config.window end
 	if config.period then predict.period = config.period end
+	-- Load dependent modules
+	if (predict.period or 0) ~= 0 and not stats then modules.load('stats') end
 	-- Reinitialize to reset timers
 	predict.deinit()
 	predict.init()

modules/predict/tests/predict.test.lua

 -- setup resolver
-modules = { 'predict' }
+modules = { 'predict', 'stats' }
 
 -- mock global functions
 local resolve_count = 0
@@ -57,4 +57,4 @@ end
 return {
 	test_predict_drain,
 	test_predict_process
-}
\ No newline at end of file
+}