This is used for making a function observable.
Can be applied to functions which are not observable by default to make them observable.



Observable

This represents the metric type - counter, that can be only increased by an integer number.



name

string

description

metricTags

This instantiates the Counter object. Name field is mandatory, and description and tags fields
are optional and have its own default values when no params are passed.



init

Description of the Counter instance. If no description is provided, the the default empty string
will be used


desc

The key/value pair of Tags. If no tags are provided, the default nil value will be used


register

Returns error if there is any metric registered already with the same name
but different parameters or in a different kind


error

Unregister the counter metric instance with the Metric Registry.


unregister

Increment the counter's value by an amount.



increment

The amount by which the value needs to be increased. The amount is defaulted as 1 and will be
used if there is no amount passed in


amount

reset

getValue

Counter

This represents the metric type - gauge, that can hold instantaneous, increased or decreased value
during the usage.



Array of StatisticConfig objects which defines about the statistical calculation
of the gauge during its usage


statisticConfigs

StatisticConfig

This instantiates the Gauge object. Name field is mandatory, and description, tags, and statitics config fields
are optional and have its own default values when no params are passed.



Description of the Gauge instance. If no description is provided, the the default empty string
will be used


Statistics configurations array is used for statistics calculation. In case if empty
statistics configurations array is passed, then statistics calculation will be disabled.
If nil () is passed, then default statistics configs will be used for the statitics
calculation


statisticConfig

Register the gauge metric instance with the Metric Registry.



Increment the gauge's value by an amount.



The amount by which the value of gauge needs to be increased.
The amount is defaulted as 1.0 and will be used if there is no amount passed in


float

Decrement the gauge's value by an amount.



decrement

The amount by which the value of gauge needs to be decreased.
The amount is defaulted as 1.0 and will be used if there is no amount passed in


Sets the instantaneous value for gauge.



setValue

The instantaneous value that needs to be set as gauge value


Retrieves statistics snapshots based on the statistics configs of the gauge.



getSnapshot

Array of the statistics snapshots.
If there is no statisticsConfigs provided, then it will be nil


Gauge

## Module Overview

This module provides an API for observing Ballerina services.
Ballerina supports Observability out of the box. This module provides an API to make observability more flexible for the Ballerina users.

To observe the Ballerina code, the '--b7a.observability.enabled=true' property should be given when starting the service
(i.e., `ballerina run hello_world.bal --b7a.observability.enabled=true').

## Tracing
Tracing provides information regarding the roundtrip of a service invocation based on the concept of spans, which are
structured in a hierarchy based on the cause and effect concept. The tracing API allows users to tap into that
tracing information, introduce new spans, and add additional information to existing spans using user-defined tags.

### Samples

#### Start a root span & attach a child span

The following code snippet shows an example of starting a root span with no parent and starting another span as a child of the first span.
Note: Make sure that all started spans are closed properly to ensure that all spans are reported properly.

```ballerina
int spanId = observe:startRootSpan("Parent Span");

// Do Something.

int spanId2 = checkpanic observe:startSpan("Child Span", parentSpanId = spanId);

// Do Something.

var ret1 = observe:finishSpan(spanId2);

// Do Something.

var ret2 = observe:finishSpan(spanId);
```

#### Start a span attached to a system trace

When no parentSpanId is given or a parentSpanId of -1 is given, a span is started as a child span to the current active span in the ootb system trace.

```ballerina
int spanId = checkpanic observe:startSpan("Child Span");

// Do Something.

var ret = observe:finishSpan(spanId);
```

#### Attach a tag to a span

It is possible to add tags to the span by using the `observe:addTagToSpan()` function by providing the span id and relevant tag key and tag value.

```ballerina
_ = observe:addTagToSpan(spanId = spanId, "Tag Key", "Tag Value");
```
#### Attach a tag to a span in the system trace
When no spanId is provided or -1 is given, the defined tags are added to the current active span in the ootb system trace.

```ballerina
var ret = observe:addTagToSpan("Tag Key", "Tag Value");
```

## Metrics
There are mainly two kind of metrics instances supported; Counter and Gauge. A counter is a cumulative metric that
represents a single monotonically increasing counter whose value can only increase or be reset to zero on restart.
For example, you can use a counter to represent the number of requests served, tasks completed, or errors.
The Gauge metric instance represents a single numerical value that can arbitrarily go up and down, and also based on the
statistics configurations provided to the Gauge, it can also report the statistics such as max, min, mean, percentiles, etc.

### Counter Samples

#### Create
The following code snippets provides the information on how Counter instances can be created. Instantiating the counter
will simply create an instance based on the params passed.

```ballerina
// Create counter with simply by name.
observe:Counter simpleCounter = new("SimpleCounter"); 

// Create counter with description.
observe:Counter counterWithDesc = new("CounterWithDesc", 
        desc = "This is a sample counter description");

// Create counter with tags.
map<string> counterTags = { "method": "GET" };
observe:Counter counterWithTags = new("CounterWithTags", 
        desc = "Some description", tags = counterTags);
```

#### Register
The counter can be registered with the global metrics registry. Therefore, it can be looked up later without having the
reference of the counter that was created. Also, only the registered counters will be reported to the Metrics reporter
such as Prometheus. In case, if there is already another non counter metric registered,
then there will be an error returned. But if it's another counter instance, then the registered counter instance will
be returned.

```ballerina
map<string> counterTags = { "method": "GET" };
observe:Counter counterWithTags = new("CounterWithTags", 
        desc = "Some description", tags = counterTags);
var anyError = counterWithTags.register();
if anyError is error {
    log:printError("Cannot register the counter", err = anyError);
}
```

#### Unregister
The counter can be unregistered with the global metrics registry if it is already registered. If a metrics is unregistered,
then further it'll not be included in metrics reporting.

```ballerina
map<string> counterTags = { "method": "GET" };
observe:Counter counterWithTags = new("CounterWithTags", 
        desc = "Some description", tags = counterTags);
var anyError = counterWithTags.register();
if anyError is error {
    log:printError("Cannot register the counter", err = anyError);
}
counterWithTags.unregister();
    
```

#### Increment
The counter can be incremented without passing any params (defaulted to 1), or by a specific amount.

```ballerina
map<string> counterTags = { "method": "GET" };
observe:Counter counterWithTags = new("CounterWithTags", 
        desc = "Some description", tags = counterTags);
// Increment by 1.
counterWithTags.increment(); 
// Increment by amount 10.
counterWithTags.increment(amount = 10);
```

#### Reset
The counter can be resetted to default amount = 0.

```ballerina
map<string> counterTags = { "method": "GET" };
observe:Counter counterWithTags = new("CounterWithTags", 
        desc = "Some description", tags = counterTags);
counterWithTags.reset();
```

#### Get Value
The current value can be retrieved by this operation.

```ballerina
map<string> counterTags = { "method": "GET" };
observe:Counter counterWithTags = new("CounterWithTags", 
        desc = "Some description", tags = counterTags);
int currentValue = counterWithTags.getValue();
```

### Gauge Samples

#### Create
The following code snippets provides the information on how Gauge instances can be created. Instantiating the gauge
will simply create an instance based on the params passed.

```ballerina
// Create gauge with simply by name. 
// Uses the default statistics configuration. 
observe:Gauge simpleGauge = new("SimpleGauge"); 

// Create gauge with description.
// Uses the default statistics configuration. 
observe:Gauge gaugeWithDesc = new("GaugeWithDesc", 
        desc = "This is a sample gauge description");

// Create gauge with tags.
// Uses the default statistics configuration. 
map<string> gaugeTags = { "method": "GET" };
observe:Counter gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);

// Create gauge with disabled statistics. 
observe:StatisticConfig[] statsConfigs = [];
observe:Gauge gaugeWithNoStats = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags, statisticConfig = statsConfigs);

// Create gauge with statistics config. 
observe:StatisticConfig config = { timeWindow: 30000, 
        percentiles: [0.33, 0.5, 0.9, 0.99], buckets: 3 };
statsConfigs[0]=config; 

observe:Gauge gaugeWithStats = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags, statisticConfig = statsConfigs);
```

#### Register
The gauge can be registered with the global metrics registry, therefore it can be looked up later without having the
reference of the gauge that was created. Also, only the registered counters will be reported to the Metrics reporter
such as Prometheus. In case, if there is already another non gauge metric registered,
then there will be an error returned. But if it's another gauge instance, then the registered gauge instance will
be returned.

```ballerina
map<string> gaugeTags = { "method": "GET" };
observe:Gauge gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);
var anyError = gaugeWithTags.register();
if anyError is error {
    log:printError("Cannot register the gauge", err = anyError);
}
```

#### Unregister
The gauge can be unregistered with the global metrics registry if it is already registered.
If a metrics is unregistered, then further it'll not be included in metrics reporting.

```ballerina
map<string> gaugeTags = { "method": "GET" };
observe:Gauge gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);
var anyError = gaugeWithTags.register();
if anyError is error {
    log:printError("Cannot register the gauge", err = anyError);
}
gaugeWithTags.unregister();
```

#### Increment
The gauge can be incremented without passing any params (defaulted to 1.0), or by a specific amount.

```ballerina
map<string> gaugeTags = { "method": "GET" };
observe:Gauge gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);
// Increment by 1.
gaugeWithTags.increment(); 
// Increment by amount 10.
gaugeWithTags.increment(amount = 10.0);  
```

#### Decrement
The gauge can be decremented without passing any params (defaulted to 1.0), or by a specific amount.

```ballerina
map<string> gaugeTags = { "method": "GET" };
observe:Gauge gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);
// Increment by 1.
gaugeWithTags.decrement(); 
// Increment by amount 10.
gaugeWithTags.decrement(amount = 10.0);
```

#### Set Value
This method sets the gauge's value with specific amount.

```ballerina
map<string> gaugeTags = { "method": "GET" };
observe:Gauge gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);
gaugeWithTags.setValue(100.0);
```

#### Get Value
The current value can be retrieved by this operation.

```ballerina
map<string> gaugeTags = { "method": "GET" };
observe:Gauge gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);
float currentValue = gaugeWithTags.getValue(); 
```

#### Get Snapshot
This method retrieves current snapshot of the statistics calculation based on the configurations passed to the gauge.
If the statistics are disabled, then it'll be returning nil ().

```ballerina
map<string> gaugeTags = { "method": "GET" };
observe:Gauge gaugeWithTags = new("GaugeWithTags", 
        desc = "Some description", tags = gaugeTags);
gaugeWithTags.setValue(1.0);
gaugeWithTags.setValue(2.0);
gaugeWithTags.setValue(3.0);

observe:Snapshot[]? summarySnapshot = gaugeWithTags.getSnapshot();
if summarySnapshot is observe:Snapshot[] {
    io:println(summarySnapshot);
} else {
    io:println("No statistics available!");
}
```

### Global Metrics Samples

#### Get All Metrics
This method returns all the metrics that are registered in the global metrics registry. This method is mainly useful for
metric reporters, where they can fetch all metrics, format those, and report.

```ballerina
observe:Metric[] metrics = observe:getAllMetrics();
foreach var metric in metrics {
    // Do something.
}
```

#### Lookup Metric
This method will lookup for the metric from the global metric registry and return it.

```ballerina
map<string> tags = { "method": "GET" };
observe:Counter|observe:Gauge|() metric = observe:lookupMetric("MetricName", 
        tags = tags);
if metric is observe:Counter {
    metric.increment(amount = 10);
} else if metric is observe:Gauge {
    metric.increment(amount = 10.0);
} else {
    io:println("No Metric Found!");
}
```


Add a key value pair as a tag to system metrics.



addTagToMetrics

tagKey

tagValue

An error if an error occurred while attaching tag to System Metrics


Add a key value pair as a tag to the span.



addTagToSpan

Id of span to which the tags should be added or -1 to add tags to the current active span


spanId

An error if an error occurred while attaching tag to the span


finishSpan

An error if an error occurred while finishing the span


Retrieve all registered metrics including default metrics from the ballerina runtime, and user defined metrics.



getAllMetrics

Metric

getMetricsProvider

getMetricsReporter

getSpanContext

Map of span context data (traceId and spanId).


getTracingProvider

isMetricsEnabled

boolean

isObservabilityEnabled

isTracingEnabled

Retrieve the specific metric that is described by the given name and tags.



lookupMetric

The key/value pair tags associated with the metric that should be looked up


startRootSpan

spanName

Start a span and create child relationship to current active span or user specified span.



startSpan

Id of the parent span or -1 if parent span should be taken from system trace


parentSpanId

This represents the generic metric record that can represent both counter and gauge.



metricType

value

If the metric is configured with statistics config, then the calculated statistics of the metric


summary

Snapshot

This represents the percentile value record.



percentile

PercentileValue

This represents the snapshot of the statistics calculation of the gauge.



The time window in which variation of the values are considered


timeWindow

The average value within the time window


mean

The standard deviation value within the time window


stdDev

The percentiles values calculated wihtin the time window


percentileValues

This represents the statistic configuration that can be used to instatiate gauge metric.



The percentiles that needs to be calculated


percentiles

The time window (in milli seconds) in which variation of the values are considered


The number of buckets used in the sliding time window


buckets

This module provides an API for observing Ballerina services.


Record: PercentileValue

Fields