Add documentation for client tracing

[garrensmith]

Add documentation for client tracing. This should include:

• How to enable it with a collector
• How to log to console (if this is possible)
• What information it provides

[garrensmith]

For the documentation, we need to make a mention around tracing and performance. Below is a rough idea of what I think we need to say:

Tracing gives deeper insight into what is happening in an application. But it can also affect the performance of your application. If the application generates a lot of spans and they need to be send to a collector, this will slow down the application. Here are some recommendations to try and avoid affecting the performance of your application

Use the bulk exporter

When using the application use the BulkSpanExporter to send the spans to a collector in batches rather than one at a time. The BulkSpanExporter waits and collects a number of spans before sending them to the collector. This isn't always useful when doing development. So in testing and development rather use the SimpleSpanProcessor. You can consider a setup as below:

import {
  
  SimpleSpanProcessor,
  BatchSpanProcessor,
} from '@opentelemetry/sdk-trace-base'


if (process.env.NODE_ENV === 'production') {
  provider.addSpanProcessor(new BatchSpanProcessor(otlpTraceExporter))
} else {
  provider.addSpanProcessor(new SimpleSpanProcessor(otlpTraceExporter))
}
    

Send only a sample of the spans

Another way to avoid a performance penalty with tracing is to (use probability sampling)[https://opentelemetry.io/docs/reference/specification/trace/tracestate-probability-sampling/] and send less spans to the collector.
This will reduce the collection cost of tracing but still give a good representation of what is happening in the application.
An example implementation would look like this:

import { TraceIdRatioBasedSampler } from '@opentelemetry/core'

const provider = new BasicTracerProvider({
    sampler: new TraceIdRatioBasedSampler(0.1),
    resource: new Resource({
      // we can define some metadata about the trace resource
      [SemanticResourceAttributes.SERVICE_NAME]: 'test-tracing-service',
      [SemanticResourceAttributes.SERVICE_VERSION]: '1.0.0',
    }),
  })

[andrew-walford-prisma]

Ah, thanks @garrensmith I'll bring your notes into my PR tomorrow.

[andrew-walford-prisma]

Note: there's a separate docs ticket for this, where I've been putting updates. Docs ticket