New interface definition after discussion.

storage/metric/interface.go

@@ -15,8 +15,14 @@ package metric
 
 import (
 	"github.com/matttproud/prometheus/model"
+	"time"
 )
 
+type StalenessPolicy struct {
+	AllowStale            bool
+	InterpolationInterval time.Duration
+}
+
 // MetricPersistence is a system for storing metric samples in a persistence
 // layer.
 type MetricPersistence interface {
@@ -37,10 +43,10 @@ type MetricPersistence interface {
 
 	GetMetricForFingerprint(f *model.Fingerprint) (*model.Metric, error)
 
-	GetFirstValue(m *model.Metric) (*model.Sample, error)
-	GetCurrentValue(m *model.Metric) (*model.Sample, error)
-	GetBoundaryValues(m *model.Metric, i *model.Interval) (*model.SampleSet, error)
-	GetRangeValues(m *model.Metric, i *model.Interval) (*model.SampleSet, error)
+	GetFirstValue(*model.Metric) (*model.Sample, error)
+	GetValueAtTime(*model.Metric, *time.Time, *StalenessPolicy) (*model.Sample, error)
+	GetBoundaryValues(*model.Metric, *model.Interval, *StalenessPolicy) (*model.Sample, *model.Sample, error)
+	GetRangeValues(*model.Metric, *model.Interval, *StalenessPolicy) (*model.SampleSet, error)
 
 	// DIAGNOSTIC FUNCTIONS PENDING DELETION BELOW HERE
 

storage/metric/leveldb/reading.go

@@ -20,7 +20,9 @@ import (
 	"github.com/matttproud/prometheus/coding/indexable"
 	"github.com/matttproud/prometheus/model"
 	dto "github.com/matttproud/prometheus/model/generated"
+	"github.com/matttproud/prometheus/storage/metric"
 	"log"
+	"time"
 )
 
 func (l *LevelDBMetricPersistence) hasIndexMetric(dto *dto.Metric) (bool, error) {
@@ -198,3 +200,19 @@ func (l *LevelDBMetricPersistence) GetMetricForFingerprint(f *model.Fingerprint)
 
 	panic("unreachable")
 }
+
+func (l *LevelDBMetricPersistence) GetBoundaryValues(m *model.Metric, i *model.Interval, s *metric.StalenessPolicy) (*model.Sample, *model.Sample, error) {
+	panic("not implemented")
+}
+
+func (l *LevelDBMetricPersistence) GetFirstValue(m *model.Metric) (*model.Sample, error) {
+	panic("not implemented")
+}
+
+func (l *LevelDBMetricPersistence) GetValueAtTime(m *model.Metric, t *time.Time, s *metric.StalenessPolicy) (*model.Sample, error) {
+	panic("not implemented")
+}
+
+func (l *LevelDBMetricPersistence) GetRangeValues(m *model.Metric, i *model.Interval, s *metric.StalenessPolicy) (*model.SampleSet, error) {
+	panic("not implemented")
+}