Consolidate metrics emit helpers

Keep the small metric emission helpers and their tests together so the metrics package has fewer one-function files.

Author: forge33

go/metrics/binlog_backlog.go

@@ -0,0 +1,76 @@
+/*
+   Copyright 2026 GitHub Inc.
+	 See https://github.com/github/gh-ost/blob/master/LICENSE
+*/
+
+package metrics
+
+import (
+	"fmt"
+	"runtime"
+)
+
+// EmitProgressGauges emits row-copy and DML progress gauges (namespace is applied by the client):
+// gh_ost.row_copy.rows_copied, gh_ost.row_copy.rows_estimate, gh_ost.dml.events_applied.
+func EmitProgressGauges(emit Emitter, rowsCopied, rowsEstimate, dmlEventsApplied int64) {
+	if emit == nil {
+		return
+	}
+	emit.Gauge("row_copy.rows_copied", float64(rowsCopied))
+	emit.Gauge("row_copy.rows_estimate", float64(rowsEstimate))
+	emit.Gauge("dml.events_applied", float64(dmlEventsApplied))
+}
+
+// EmitBinlogBacklogGauges emits apply-events queue depth gauges (namespace is applied by the client):
+// gh_ost.binlog.backlog_size, gh_ost.binlog.backlog_capacity, gh_ost.binlog.backlog_utilization.
+func EmitBinlogBacklogGauges(emit Emitter, backlogSize, backlogCapacity int) {
+	if emit == nil {
+		return
+	}
+	emit.Gauge("binlog.backlog_size", float64(backlogSize))
+	emit.Gauge("binlog.backlog_capacity", float64(backlogCapacity))
+	emit.Gauge("binlog.backlog_utilization", binlogBacklogUtilization(backlogSize, backlogCapacity))
+}
+
+func binlogBacklogUtilization(backlogSize, backlogCapacity int) float64 {
+	if backlogCapacity <= 0 {
+		return 0
+	}
+	utilization := float64(backlogSize) / float64(backlogCapacity)
+	if utilization > 1 {
+		return 1
+	}
+	if utilization < 0 {
+		return 0
+	}
+	return utilization
+}
+
+// EmitLagGauges emits replication and heartbeat lag gauges (namespace is applied by the client):
+// gh_ost.lag.replication_seconds, gh_ost.lag.heartbeat_seconds, each tagged throttled:true|false.
+//
+// These are point-in-time readings each status tick (not a distribution), so gauges are used
+// rather than histograms; DogStatsD histogram aggregation exposes count/max series that do not
+// match the log line lag values in Prometheus/Grafana.
+func EmitLagGauges(emit Emitter, replicationLagSeconds, heartbeatLagSeconds float64, throttled bool) {
+	if emit == nil {
+		return
+	}
+	tags := []string{fmt.Sprintf("throttled:%t", throttled)}
+	emit.Gauge("lag.replication_seconds", replicationLagSeconds, tags...)
+	emit.Gauge("lag.heartbeat_seconds", heartbeatLagSeconds, tags...)
+}
+
+// EmitGoRuntimeGauges emits gh_ost.go_runtime.* gauges (namespace is applied by the client).
+// m and numGoroutine are typically from runtime.ReadMemStats and runtime.NumGoroutine.
+func EmitGoRuntimeGauges(emit Emitter, m *runtime.MemStats, numGoroutine int) {
+	if emit == nil || m == nil {
+		return
+	}
+	emit.Gauge("go_runtime.alloc_bytes", float64(m.Alloc))
+	emit.Gauge("go_runtime.sys_bytes", float64(m.Sys))
+	emit.Gauge("go_runtime.heap_inuse_bytes", float64(m.HeapInuse))
+	emit.Gauge("go_runtime.num_gc", float64(m.NumGC))
+	emit.Gauge("go_runtime.gc_pause_total_ns", float64(m.PauseTotalNs))
+	emit.Gauge("go_runtime.goroutines", float64(numGoroutine))
+}

go/metrics/binlog_backlog_test.go

@@ -0,0 +1,174 @@
+/*
+   Copyright 2026 GitHub Inc.
+	 See https://github.com/github/gh-ost/blob/master/LICENSE
+*/
+
+package metrics
+
+import (
+	"runtime"
+	"testing"
+)
+
+type gaugeSpy struct {
+	names  []string
+	values []float64
+	tags   [][]string
+}
+
+func (g *gaugeSpy) Gauge(name string, value float64, tags ...string) {
+	g.names = append(g.names, name)
+	g.values = append(g.values, value)
+	g.tags = append(g.tags, append([]string(nil), tags...))
+}
+
+func (g *gaugeSpy) Count(name string, value int64, tags ...string) {
+}
+
+func (g *gaugeSpy) Histogram(name string, value float64, tags ...string) {
+}
+
+func TestEmitProgressGauges(t *testing.T) {
+	spy := &gaugeSpy{}
+	EmitProgressGauges(spy, 1000, 5000, 42)
+
+	wantNames := []string{
+		"row_copy.rows_copied",
+		"row_copy.rows_estimate",
+		"dml.events_applied",
+	}
+	wantVals := []float64{1000, 5000, 42}
+
+	if len(spy.names) != len(wantNames) {
+		t.Fatalf("got %d gauges, want %d", len(spy.names), len(wantNames))
+	}
+	for i := range wantNames {
+		if spy.names[i] != wantNames[i] || spy.values[i] != wantVals[i] {
+			t.Fatalf("[%d] got %s=%v want %s=%v", i, spy.names[i], spy.values[i], wantNames[i], wantVals[i])
+		}
+	}
+}
+
+func TestEmitProgressGauges_nilSafe(t *testing.T) {
+	EmitProgressGauges(nil, 1, 2, 3)
+}
+
+func TestEmitBinlogBacklogGauges(t *testing.T) {
+	spy := &gaugeSpy{}
+	EmitBinlogBacklogGauges(spy, 250, 1000)
+
+	wantNames := []string{
+		"binlog.backlog_size",
+		"binlog.backlog_capacity",
+		"binlog.backlog_utilization",
+	}
+	wantVals := []float64{250, 1000, 0.25}
+
+	if len(spy.names) != len(wantNames) {
+		t.Fatalf("got %d gauges, want %d", len(spy.names), len(wantNames))
+	}
+	for i := range wantNames {
+		if spy.names[i] != wantNames[i] || spy.values[i] != wantVals[i] {
+			t.Fatalf("[%d] got %s=%v want %s=%v", i, spy.names[i], spy.values[i], wantNames[i], wantVals[i])
+		}
+	}
+}
+
+func TestEmitBinlogBacklogGauges_nilSafe(t *testing.T) {
+	EmitBinlogBacklogGauges(nil, 1, 2)
+}
+
+func TestBinlogBacklogUtilization(t *testing.T) {
+	tests := []struct {
+		size, capacity int
+		want           float64
+	}{
+		{0, 1000, 0},
+		{250, 1000, 0.25},
+		{1000, 1000, 1},
+		{1500, 1000, 1},
+		{-1, 1000, 0},
+		{10, 0, 0},
+	}
+	for _, tt := range tests {
+		got := binlogBacklogUtilization(tt.size, tt.capacity)
+		if got != tt.want {
+			t.Fatalf("utilization(%d, %d) = %v, want %v", tt.size, tt.capacity, got, tt.want)
+		}
+	}
+}
+
+func TestEmitLagGauges_notThrottled(t *testing.T) {
+	spy := &gaugeSpy{}
+	EmitLagGauges(spy, 2.5, 1.25, false)
+
+	wantNames := []string{"lag.replication_seconds", "lag.heartbeat_seconds"}
+	wantVals := []float64{2.5, 1.25}
+	wantTags := []string{"throttled:false"}
+
+	if len(spy.names) != len(wantNames) {
+		t.Fatalf("got %d gauges, want %d", len(spy.names), len(wantNames))
+	}
+	for i := range wantNames {
+		if spy.names[i] != wantNames[i] || spy.values[i] != wantVals[i] {
+			t.Fatalf("[%d] got %s=%v want %s=%v", i, spy.names[i], spy.values[i], wantNames[i], wantVals[i])
+		}
+		if len(spy.tags[i]) != 1 || spy.tags[i][0] != wantTags[0] {
+			t.Fatalf("[%d] got tags %v want [%s]", i, spy.tags[i], wantTags[0])
+		}
+	}
+}
+
+func TestEmitLagGauges_throttled(t *testing.T) {
+	spy := &gaugeSpy{}
+	EmitLagGauges(spy, 4.0, 3.0, true)
+
+	if len(spy.names) != 2 {
+		t.Fatalf("got %d gauges, want 2", len(spy.names))
+	}
+	for i := range spy.names {
+		if len(spy.tags[i]) != 1 || spy.tags[i][0] != "throttled:true" {
+			t.Fatalf("[%d] got tags %v want [throttled:true]", i, spy.tags[i])
+		}
+	}
+}
+
+func TestEmitLagGauges_nilSafe(t *testing.T) {
+	EmitLagGauges(nil, 1, 2, false)
+}
+
+func TestEmitGoRuntimeGauges(t *testing.T) {
+	spy := &gaugeSpy{}
+	m := &runtime.MemStats{
+		Alloc:        100,
+		Sys:          200,
+		HeapInuse:    300,
+		NumGC:        7,
+		PauseTotalNs: 42,
+	}
+	EmitGoRuntimeGauges(spy, m, 123)
+
+	wantNames := []string{
+		"go_runtime.alloc_bytes",
+		"go_runtime.sys_bytes",
+		"go_runtime.heap_inuse_bytes",
+		"go_runtime.num_gc",
+		"go_runtime.gc_pause_total_ns",
+		"go_runtime.goroutines",
+	}
+	wantVals := []float64{100, 200, 300, 7, 42, 123}
+
+	if len(spy.names) != len(wantNames) {
+		t.Fatalf("got %d gauges, want %d", len(spy.names), len(wantNames))
+	}
+	for i := range wantNames {
+		if spy.names[i] != wantNames[i] || spy.values[i] != wantVals[i] {
+			t.Fatalf("[%d] got %s=%v want %s=%v", i, spy.names[i], spy.values[i], wantNames[i], wantVals[i])
+		}
+	}
+}
+
+func TestEmitGoRuntimeGauges_nilSafe(t *testing.T) {
+	EmitGoRuntimeGauges(nil, &runtime.MemStats{}, 1)
+	EmitGoRuntimeGauges(&gaugeSpy{}, nil, 1)
+}

go/metrics/emit.go

@@ -11,20 +11,6 @@ import (
 	"time"
 )
 
-// EmitGoRuntimeGauges emits gh_ost.go_runtime.* gauges (namespace is applied by the client).
-// m and numGoroutine are typically from runtime.ReadMemStats and runtime.NumGoroutine.
-func EmitGoRuntimeGauges(emit Emitter, m *runtime.MemStats, numGoroutine int) {
-	if emit == nil || m == nil {
-		return
-	}
-	emit.Gauge("go_runtime.alloc_bytes", float64(m.Alloc))
-	emit.Gauge("go_runtime.sys_bytes", float64(m.Sys))
-	emit.Gauge("go_runtime.heap_inuse_bytes", float64(m.HeapInuse))
-	emit.Gauge("go_runtime.num_gc", float64(m.NumGC))
-	emit.Gauge("go_runtime.gc_pause_total_ns", float64(m.PauseTotalNs))
-	emit.Gauge("go_runtime.goroutines", float64(numGoroutine))
-}
-
 // StartGoRuntimeReporter periodically samples runtime memory and goroutines and emits gauges
 // until ctx is cancelled. It is a no-op when interval <= 0, client is nil, or StatsD is disabled
 // (noop client).