Instrument Go segments

With New Relic APM for Go, you can monitor the specific segments of a transaction in a Go application to get more detail about specific functions or code blocks.

For general information about New Relic's Go monitoring, see New Relic for Go.

What is a segment?

Segments are the specific parts of a transaction in an application. By instrumenting segments, you can measure the time taken by functions and code blocks, such as external calls, datastore calls, and background tasks.

Here's one example of why you might instrument specific segments:

You have a transaction associated with a checkout process, which processes both shipping information and credit card information. You could instrument your application to break that transaction up into two pieces: one segment for shipping and one segment for payment.

Block-of-code segments

Once you instrument a transaction, you are ready to instrument one or more segments in that transaction.

To instrument an arbitrary block of code as a segment, use the following pattern:

segment := newrelic.Segment{}
segment.Name = "mySegmentName"
segment.StartTime = newrelic.StartSegmentNow(txn)
// ... code you want to time here ...
segment.End()

txn is the variable name set for the transaction, as described in Instrument Go transactions.

StartSegment is a convenient helper. It creates a segment and starts it:

segment := newrelic.StartSegment(txn, "mySegmentName")
// ... code you want to time here ...
segment.End()

Function segments

Instrumenting a function as a segment is essentially the same as instrumenting an arbitrary block of code as a segment. The main difference is that, because a function has a discrete ending, you can use Go's defer statement.

To instrument a function as a segment, add the following code at the start of the function:

defer newrelic.StartSegment(txn, "mySegmentName").End()

txn is the variable name set for the transaction, as described in Instrument Go transactions.

Nest segments

Segments can be nested. The segment being ended must be the most recently started segment.

Here's an example of a segment starting and ending inside another segment:

s1 := newrelic.StartSegment(txn, "outerSegment")
s2 := newrelic.StartSegment(txn, "innerSegment")
// s2 must end before s1
s2.End()
s1.End()

A zero value segment may safely be ended. Therefore, the following code is safe even if the conditional fails:

var s newrelic.Segment
if txn, ok := w.(newrelic.Transaction); ok {
    s.StartTime = newrelic.StartSegmentNow(txn),
}
// ... code you wish to time here ...
s.End()

Datastore segments

You can instrument Go application datastore calls. Datastore segments appear in the Breakdown table and Databases tab of the Transactions page in the New Relic UI.

Just like basic segments, datastore segments begin when the StartTime field is populated and finish when the End method is called. To instrument a datastore segment, place the following at the beginning of the function you want to monitor:

s := newrelic.DatastoreSegment{
    Product: newrelic.DatastoreMySQL,
    Collection: "users",
    Operation: "INSERT",
    ParameterizedQuery: "INSERT INTO users (name, age) VALUES ($1, $2)",
    QueryParameters: map[string]interface{}{
        "name": "Dracula",
        "age": 439,
    },
    Host: "mysql-server-1",
    PortPathOrID: "3306",
    DatabaseName: "my_database",
}
s.StartTime = newrelic.StartSegmentNow(txn)
// ... make the datastore call
s.End()

For more on how to assign the Product, Collection, Operation, and other parameter values, see the New Relic datastore segment documentation on GitHub.

When instrumenting a datastore call that spans an entire function call, you can use the defer statement to simplify instrumentation:

defer newrelic.DatastoreSegment{
    Product: newrelic.DatastoreMySQL,
    Collection: "users",
    Operation: "INSERT",
    ParameterizedQuery: "INSERT INTO users (name, age) VALUES ($1, $2)",
    QueryParameters: map[string]interface{}{
        "name": "Dracula",
        "age": 439,
    },
    Host: "mysql-server-1",
    PortPathOrID: "3306",
    DatabaseName: "my_database",
}.End()

External segments

You can instrument Go application calls to external services, such as web services, resources in the cloud, and any other network calls. External segments appear in the Breakdown table and the External services page of the New Relic UI.

There are two ways to instrument external segments:

Use StartExternalSegment()

New Relic recommends using the StartExternalSegment helper, since New Relic uses it to trace activity between your New Relic applications using Cross Application Tracing.

func external(txn newrelic.Transaction, req *http.Request) (*http.Response, error) {
    s := newrelic.StartExternalSegment(txn, req)
    response, err := http.DefaultClient.Do(req)
    s.Response = response
    s.End()
    return response, err
}
 
Use NewRoundTripper()

The NewRoundTripper method is an optional helper built on top of PrepareRequest and EndRequest. It accesses the Go RoundTripper interface, which allows special control over HTTP request execution. It must be used in the same goroutine as the transaction.

Here is an example of NewRoundTripper instrumentation:

client := &http.Client{}
client.Transport = newrelic.NewRoundTripper(txn, nil)
resp, err := client.Get("http://example.com/")

For more help

Recommendations for learning more: