feat(observability/metrics): add Emitter, options, buckets, and label vocabulary by xytan0056 · Pull Request #181 · uber/tango

xytan0056 · 2026-07-11T02:42:31Z

Adds the observability/metrics package: the Emitter interface with a tally-backed implementation, per-call options (WithTags, duration/value bucket overrides), the default histogram buckets, and the shared tag keys + Result values.

Operation and metric names are added in later PRs as their emitters land, so nothing here is unused.
single Option type across emitter. Per-method option types is overkill for 3 options. Unintended options are noop anyway.

Stacked on #158.

xytan0056 · 2026-07-11T02:49:18Z

+	ResultFail    Result = "fail"
+	ResultHit     Result = "hit"
+	ResultMiss    Result = "miss"
+)


rest of consts will be added as used. Keeping the change incremental for easier review

sywhang · 2026-07-12T04:42:22Z

+
+// Emitter is the interface for emitting metrics.
+type Emitter interface {
+	Inc(op, name string, opts ...Option)


these methods should all be documented

sywhang · 2026-07-12T04:43:39Z

+	"github.com/uber-go/tally"
+)
+
+func counterValue(t *testing.T, s tally.TestScope, name string, tags map[string]string) int64 {


style: helpers should be placed below the tests.

sywhang · 2026-07-12T04:44:05Z

+// limitations under the License.
+
+// Package metrics is a thin wrapper over tally.Scope that pins the naming,
+// bucket, and tag conventions defined in the Tango Metrics Inventory.


what is this "Tango Metrics Inventory"? It's better to document these in the package doc directly rather than just referencing something.

sywhang · 2026-07-12T04:45:28Z

+)
+
+// Emitter is the interface for emitting metrics.
+type Emitter interface {


now that we've written it out, I'm not sure if we want Emitter to be an interface or a struct since we only have a single implementation of it.

The only reason this might be useful is if people want to plug in metrics emitter that are not backed by Tally, but that seems unlikely -- Thoughts?

with interface, downstream can just New(nil) without Tally.NewTestScope (which is not bad either). This also forces construction here, with exporting struct,people can do metrics.Emitter{}, which can panic with nil scope

uber internal (duplica server) can implement this interface for consistency, not necessarily required tho

I think the whole purpose of Emitter interface is to have it potentially pluggable and not depend on Tally.
The alternative approach (this is done in sqv2) is to use Tally as is with a potentially customized backend, because Tally itself is an abstraction.

… vocabulary

sbalabanov · 2026-07-13T18:42:11Z

+)
+
+// Emitter is the interface for emitting metrics.
+type Emitter interface {


I think the whole purpose of Emitter interface is to have it potentially pluggable and not depend on Tally.
The alternative approach (this is done in sqv2) is to use Tally as is with a potentially customized backend, because Tally itself is an abstraction.

sbalabanov · 2026-07-13T18:44:42Z

+	// the default duration buckets unless overridden with WithDurationBuckets.
+	RecordDur(op, name string, d time.Duration, opts ...Option)
+	// RecordCount records v in the named histogram under the op subscope, using
+	// the default value buckets unless overridden with WithValueBuckets.


where practically will it be used?
I think the only reason to record into histogram is a duration, otherwise it is simply a counter with tags.

this is for recording targets count from changedtargets call. This way we have an idea of repo scale and sanity of response
counter (by Inc) is for recording traffic trends

sbalabanov · 2026-07-13T18:46:00Z

+
+// Result values for TagResult.
+const (
+	ResultSuccess Result = "success"


all exported times are to be commented

these are self-explanatory constants, I'm going to add more later for operations, adding a comment to each of them seems a bit redundant

Single implementation and a thin tally wrapper — drop the interface and export the struct directly. New/Tagged return *Emitter. Callers fake metrics with tally.NewTestScope, not an interface mock.

xytan0056 and others added 3 commits July 8, 2026 20:59

docs(observability/metrics): document the metrics package

59d8c93

Update metrics.md

4293ff1

Update metrics.md

2a4d0f3

xytan0056 requested review from a team as code owners July 11, 2026 02:42

xytan0056 mentioned this pull request Jul 11, 2026

feat(observability/metrics): add TrackInFlight helper #182

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xytan0056 force-pushed the pr1-emitter-core branch from b879ee5 to 4a55fde Compare July 11, 2026 02:47

xytan0056 commented Jul 11, 2026

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xytan0056 force-pushed the pr1-emitter-core branch 2 times, most recently from cd500a7 to 7e2b539 Compare July 11, 2026 03:08

xytan0056 changed the title ~~[WIP] feat(observability/metrics): add Emitter, options, buckets, and label vocabulary~~ \\feat(observability/metrics): add Emitter, options, buckets, and label vocabulary Jul 11, 2026

xytan0056 changed the title ~~\\feat(observability/metrics): add Emitter, options, buckets, and label vocabulary~~ feat(observability/metrics): add Emitter, options, buckets, and label vocabulary Jul 11, 2026

sywhang reviewed Jul 12, 2026

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xytan0056 force-pushed the pr1-emitter-core branch 2 times, most recently from 8ee7643 to 7e2b539 Compare July 12, 2026 22:16

feat(observability/metrics): add Emitter, options, buckets, and label…

300d46c

… vocabulary

xytan0056 force-pushed the pr1-emitter-core branch from 7e2b539 to 300d46c Compare July 12, 2026 22:41

sbalabanov reviewed Jul 13, 2026

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refactor(observability/metrics): make Emitter a concrete struct

53a8e41

Single implementation and a thin tally wrapper — drop the interface and export the struct directly. New/Tagged return *Emitter. Callers fake metrics with tally.NewTestScope, not an interface mock.

xytan0056 force-pushed the pr1-emitter-core branch from 60dae4c to 53a8e41 Compare July 14, 2026 05:53

xytan0056 force-pushed the pr0-docs branch 2 times, most recently from 4371e62 to f6e4228 Compare July 15, 2026 05:19

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feat(observability/metrics): add Emitter, options, buckets, and label vocabulary#181

feat(observability/metrics): add Emitter, options, buckets, and label vocabulary#181
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