add optional params

Author: mayurkale22

metrics/Gauge.md

@@ -10,12 +10,12 @@ The value that is published for gauges is an instantaneous measurement of an `in
 The following general operations MUST be provided by the API:
 * Defining a `name`, `description`, `unit`, `labelKeys`, `resource` and `constantLabels` which are fixed labels that always apply to a gauge. This should give back the gauge object to get or create time series, remove time series and clear all time series.
 	* `name`: a string describing the name of the metric, e.g. "vm_cpu_cycles" or "queue_size". Names MUST be unique within the library. It is recommended to use names compatible with the intended end usage.
-	* `description`: a string describing the metric, e.g."Virtual cycles executed on VM".
-	* `unit`: a string describing the unit used for the metric (default set to "1"). Follows the format described by
-[Unified Code for Units of Measure](http://unitsofmeasure.org/ucum.html).
-	* `labelKeys`: the list of the label keys to track different types of metric.
-	* `constantLabels`: the map of label keys and label values. The keys in `labelKeys` must not be present in this map.
-	* `resource`: the optional associated monitored resource information.
+	* `description`: an optional string describing the metric, e.g."Virtual cycles executed on VM". The default is set to "".
+	* `unit`: an optional string describing the unit used for the metric. Follows the format described by
+[Unified Code for Units of Measure](http://unitsofmeasure.org/ucum.html). The default set to "1".
+	* `labelKeys`: an optional list of the label keys to track different types of metric. The default is set to empty list.
+	* `constantLabels`: an optional map of label keys and label values. The default is set to empty map.
+	* `resource`: an optional associated monitored resource information.
 * Add a new time series with label values, which returns a `Point` (which is part of the `TimeSeries`). Each point represents an instantaneous measurement of a varying gauge value. Each Gauge Metric has one or more time series for a single metric.
 	* `labelValues`: the list of label values. The number of label values must be the same to that of the label keys.
 * The `Point` class should provide functionalities to manually increment/decrement values. Example: `add(long amt)`, `set(long value)`.
@@ -48,7 +48,7 @@ void doSomeWork() {
    point.set(15);
 }
 ```
-It is recommended to keep a reference of a point for manual operations instead of always calling `getOrCreateTimeSeries` method.
+It is recommended to keep a reference of a point for manual operations instead of always calling `getOrCreateTimeSeries` method. The keys in `labelKeys` must not be present in `constantLabels` map. Also, `constantLabels` will be added to all the timeseries for the Metric.
 
 ## Derived Gauge API
 
@@ -57,12 +57,12 @@ The value that is published for gauges is an instantaneous measurement of an `in
 The following general operations MUST be provided by the API:
 * Defining a `name`, `description`, `unit`, `labelKeys`, `resource` and `constantLabels` which are fixed labels that always apply to a gauge. This should give back gauge object to add new time series, remove time series and clear all time series.
 	* `name`: a string describing the name of the metric, e.g. "vm_cpu_cycles". Names MUST be unique within the library. It is recommended to use names compatible with the intended end usage.
-	* `description`: a string describing the metric, e.g."Virtual cycles executed on VM".
-	* `unit`: a string describing the unit used for the metric (default set to "1"). Follows the format described by
-[Unified Code for Units of Measure](http://unitsofmeasure.org/ucum.html).
-	* `labelKeys`: the list of the label keys to track different types of metric.
-	* `constantLabels`: the map of label keys and label values. The keys in `labelKeys` must not be present in this map.
-	* `resource`: the optional associated monitored resource information.
+	* `description`: an optional string describing the metric, e.g."Virtual cycles executed on VM". The default is set to "".
+	* `unit`: an optional string describing the unit used for the metric. Follows the format described by
+[Unified Code for Units of Measure](http://unitsofmeasure.org/ucum.html). The default set to "1".
+	* `labelKeys`: an optional list of the label keys to track different types of metric. The default is set to empty list.
+	* `constantLabels`: an optional map of label keys and label values. The default is set to empty map.
+	* `resource`: an optional associated monitored resource information.
 * Add a new time series with label values, an `object` and a `callback function`. The number of label values must be the same to that of the label keys.
 	* `labelValues`: the list of label values. The number of label values must be the same to that of the label keys.
 	* `object`: the state object from which the function derives a measurement.