add CachedSignatureWeightPercentage metric

as discussed on standup

signature-aggregator/aggregator/aggregator.go

@@ -152,6 +152,12 @@ func (s *SignatureAggregator) CreateSignedMessage(
 			}
 		}
 		s.metrics.SignatureCacheHits.Add(float64(len(signatureMap)))
+		s.metrics.CachedSignatureWeightPercentage.Set(
+			float64(utils.GetStakeWeightPercentage(
+				accumulatedSignatureWeight,
+				connectedValidators.TotalValidatorWeight,
+			)),
+		)
 	}
 	if signedMsg, err := s.aggregateIfSufficientWeight(
 		unsignedMessage,

signature-aggregator/metrics/metrics.go

@@ -31,6 +31,7 @@ var Opts = struct {
 	InvalidSignatureResponses          prometheus.CounterOpts
 	SignatureCacheHits                 prometheus.CounterOpts
 	SignatureCacheMisses               prometheus.CounterOpts
+	CachedSignatureWeightPercentage    prometheus.GaugeOpts
 }{
 	AggregateSignaturesLatencyMS: prometheus.GaugeOpts{
 		Name: "agg_sigs_latency_ms",
@@ -72,6 +73,10 @@ var Opts = struct {
 		Name: "signature_cache_misses",
 		Help: "Number of signatures that were not found in the cache",
 	},
+	CachedSignatureWeightPercentage: prometheus.GaugeOpts{
+		Name: "cached_signature_weight_percentage",
+		Help: "The percentage of stake weight represented by the cached signatures for a given warp message ID",
+	},
 }
 
 type SignatureAggregatorMetrics struct {
@@ -85,6 +90,7 @@ type SignatureAggregatorMetrics struct {
 	InvalidSignatureResponses          prometheus.Counter
 	SignatureCacheHits                 prometheus.Counter
 	SignatureCacheMisses               prometheus.Counter
+	CachedSignatureWeightPercentage    prometheus.Gauge
 
 	// TODO: consider other failures to monitor. Issue #384 requires
 	// "network failures", but we probably don't handle those directly.
@@ -129,6 +135,9 @@ func NewSignatureAggregatorMetrics(
 		SignatureCacheMisses: prometheus.NewCounter(
 			Opts.SignatureCacheMisses,
 		),
+		CachedSignatureWeightPercentage: prometheus.NewGauge(
+			Opts.CachedSignatureWeightPercentage,
+		),
 	}
 
 	registerer.MustRegister(m.AggregateSignaturesLatencyMS)
@@ -141,6 +150,7 @@ func NewSignatureAggregatorMetrics(
 	registerer.MustRegister(m.InvalidSignatureResponses)
 	registerer.MustRegister(m.SignatureCacheHits)
 	registerer.MustRegister(m.SignatureCacheMisses)
+	registerer.MustRegister(m.CachedSignatureWeightPercentage)
 
 	return &m
 }

tests/signature_aggregator_api.go

@@ -131,6 +131,7 @@ func SignatureAggregatorAPI(network interfaces.LocalNetwork) {
 		{metrics.Opts.InvalidSignatureResponses.Name, "==", 0},
 		{metrics.Opts.SignatureCacheHits.Name, "==", 0},
 		{metrics.Opts.SignatureCacheMisses.Name, "==", 0},
+		{metrics.Opts.CachedSignatureWeightPercentage.Name, "==", 0},
 	} {
 		Expect(metricsSample[m.name]).Should(
 			BeNumerically(m.op, m.value),
@@ -157,6 +158,9 @@ func SignatureAggregatorAPI(network interfaces.LocalNetwork) {
 	Expect(
 		metricsSample2[metrics.Opts.SignatureCacheMisses.Name],
 	).Should(Equal(metricsSample[metrics.Opts.SignatureCacheMisses.Name]))
+	Expect(
+		metricsSample2[metrics.Opts.CachedSignatureWeightPercentage.Name],
+	).Should(BeNumerically("==", 75))
 }
 
 // returns a map of metric names to metric samples
@@ -185,6 +189,7 @@ func sampleMetrics(port uint16) map[string]uint64 {
 			metrics.Opts.InvalidSignatureResponses.Name,
 			metrics.Opts.SignatureCacheHits.Name,
 			metrics.Opts.SignatureCacheMisses.Name,
+			metrics.Opts.CachedSignatureWeightPercentage.Name,
 		} {
 			if strings.HasPrefix(
 				line,

utils/utils.go

@@ -54,6 +54,22 @@ func CheckStakeWeightExceedsThreshold(
 	return scaledTotalWeight.Cmp(scaledSigWeight) != 1
 }
 
+func GetStakeWeightPercentage(
+	proportionalWeight *big.Int,
+	totalWeight uint64,
+) uint64 {
+	totalWeightBI := new(big.Int).SetUint64(totalWeight)
+	scaledProportionalWeight := new(big.Int).Mul(
+		proportionalWeight,
+		new(big.Int).SetUint64(100),
+	)
+	percentage := scaledProportionalWeight.Div(
+		scaledProportionalWeight,
+		totalWeightBI,
+	)
+	return percentage.Uint64()
+}
+
 // Wrapper for CheckStakeWeightExceedThreshold with a quorumDen of 100.
 func CheckStakeWeightPercentageExceedsThreshold(
 	accumulatedSignatureWeight *big.Int,