# Observability Analysis Language
Provide OAL(Observability Analysis Language) to analysis incoming data in streaming mode. 

OAL focuses on metric in Service, Service Instance and Endpoint. Because of that, the language is easy to 
learn and use.

Considering performance, reading and debugging, OAL is defined as a compile language. 
The OAL scripts will be compiled to normal Java codes in package stage.

## Grammar
Scripts should be named as `*.oal`
```

METRIC_NAME = from(SCOPE.(* | [FIELD][,FIELD ...]))
[.filter(FIELD OP [INT | STRING])]
.FUNCTION([PARAM][, PARAM ...])
```

## Scope
Primary **SCOPE**s are `All`, `Service`, `ServiceInstance`, `Endpoint`, `ServiceRelation`, `ServiceInstanceRelation`, `EndpointRelation`.
Also there are some secondary scopes, which belongs to one primary scope. 

Read [Scope Definitions](scope-definitions.md), you can find all existing Scopes and Fields.


## Filter
Use filter to build the conditions for the value of fields, by using field name and expression. 

The expressions support to link by `and`, `or` and `(...)`. 
The OPs support `=`, `!=`, `>`, `<`, `in (v1, v2, ...`, `like "%..."`, with type detection based of field type. Trigger compile
 or code generation error if incompatible. 

## Aggregation Function
The default functions are provided by SkyWalking OAP core, and could implement more. 

Provided functions
- `longAvg`. The avg of all input per scope entity. The input field must be a long.
> instance_jvm_memory_max = from(ServiceInstanceJVMMemory.max).longAvg();

In this case, input are request of each ServiceInstanceJVMMemory scope, avg is based on field `max`.
- `doubleAvg`. The avg of all input per scope entity. The input field must be a double.
> instance_jvm_cpu = from(ServiceInstanceJVMCPU.usePercent).doubleAvg();

In this case, input are request of each ServiceInstanceJVMCPU scope, avg is based on field `usePercent`.
- `percent`. The number or ratio expressed as a fraction of 100, for the condition matched input.
> endpoint_percent = from(Endpoint.*).percent(status == true);

In this case, all input are requests of each endpoint, condition is `endpoint.status == true`.
- `sum`. The sum calls per scope entity.
> Service_Calls_Sum = from(Service.*).sum();

In this case, calls of each service. 
- `p99`, `p95`, `p90`, `p75`, `p50`. Read [p99 in WIKI](https://en.wikipedia.org/wiki/Percentile)
> All_p99 = from(All.latency).p99(10);

In this case, p99 value of all incoming requests.
- `thermodynamic`. Read [Heatmap in WIKI](https://en.wikipedia.org/wiki/Heat_map))
> All_heatmap = from(All.latency).thermodynamic(100, 20);

In this case, thermodynamic heatmap of all incoming requests.

## Metric name
The metric name for storage implementor, alarm and query modules. The type inference supported by core.

## Group
All metric data will be grouped by Scope.ID and min-level TimeBucket. 

- In `Endpoint` scope, the Scope.ID = Endpoint id (the unique id based on service and its Endpoint)

## Examples
```
// Caculate p99 of both Endpoint1 and Endpoint2
Endpoint_p99 = from(Endpoint.latency).filter(name in ("Endpoint1", "Endpoint2")).summary(0.99)

// Caculate p99 of Endpoint name started with `serv`
serv_Endpoint_p99 = from(Endpoint.latency).filter(name like ("serv%")).summary(0.99)

// Caculate the avg response time of each Endpoint
Endpoint_avg = from(Endpoint.latency).avg()

// Caculate the histogram of each Endpoint by 50 ms steps.
// Always thermodynamic diagram in UI matches this metric. 
Endpoint_histogram = from(Endpoint.latency).histogram(50)

// Caculate the percent of response status is true, for each service.
Endpoint_success = from(Endpoint.*).filter(status = "true").percent()

// Caculate the percent of response code in [200, 299], for each service.
Endpoint_200 = from(Endpoint.*).filter(responseCode like "2%").percent()

// Caculate the percent of response code in [500, 599], for each service.
Endpoint_500 = from(Endpoint.*).filter(responseCode like "5%").percent()

// Caculate the sum of calls for each service.
EndpointCalls = from(Endpoint.*).sum()
```