Change Metric Processor to merge multiple observations

sdk/metric/controller/pull/pull_test.go

@@ -41,7 +41,7 @@ func TestPullNoCache(t *testing.T) {
 
 	ctx := context.Background()
 	meter := puller.Provider().Meter("nocache")
-	counter := metric.Must(meter).NewInt64Counter("counter")
+	counter := metric.Must(meter).NewInt64Counter("counter.sum")
 
 	counter.Add(ctx, 10, kv.String("A", "B"))
 
@@ -50,8 +50,8 @@ func TestPullNoCache(t *testing.T) {
 	require.NoError(t, puller.ForEach(export.CumulativeExporter, records.AddRecord))
 
 	require.EqualValues(t, map[string]float64{
-		"counter/A=B/": 10,
-	}, records.Map)
+		"counter.sum/A=B/": 10,
+	}, records.Map())
 
 	counter.Add(ctx, 10, kv.String("A", "B"))
 
@@ -60,8 +60,8 @@ func TestPullNoCache(t *testing.T) {
 	require.NoError(t, puller.ForEach(export.CumulativeExporter, records.AddRecord))
 
 	require.EqualValues(t, map[string]float64{
-		"counter/A=B/": 20,
-	}, records.Map)
+		"counter.sum/A=B/": 20,
+	}, records.Map())
 }
 
 func TestPullWithCache(t *testing.T) {
@@ -75,7 +75,7 @@ func TestPullWithCache(t *testing.T) {
 
 	ctx := context.Background()
 	meter := puller.Provider().Meter("nocache")
-	counter := metric.Must(meter).NewInt64Counter("counter")
+	counter := metric.Must(meter).NewInt64Counter("counter.sum")
 
 	counter.Add(ctx, 10, kv.String("A", "B"))
 
@@ -84,8 +84,8 @@ func TestPullWithCache(t *testing.T) {
 	require.NoError(t, puller.ForEach(export.CumulativeExporter, records.AddRecord))
 
 	require.EqualValues(t, map[string]float64{
-		"counter/A=B/": 10,
-	}, records.Map)
+		"counter.sum/A=B/": 10,
+	}, records.Map())
 
 	counter.Add(ctx, 10, kv.String("A", "B"))
 
@@ -95,8 +95,8 @@ func TestPullWithCache(t *testing.T) {
 	require.NoError(t, puller.ForEach(export.CumulativeExporter, records.AddRecord))
 
 	require.EqualValues(t, map[string]float64{
-		"counter/A=B/": 10,
-	}, records.Map)
+		"counter.sum/A=B/": 10,
+	}, records.Map())
 
 	mock.Add(time.Second)
 	runtime.Gosched()
@@ -107,7 +107,7 @@ func TestPullWithCache(t *testing.T) {
 	require.NoError(t, puller.ForEach(export.CumulativeExporter, records.AddRecord))
 
 	require.EqualValues(t, map[string]float64{
-		"counter/A=B/": 20,
-	}, records.Map)
+		"counter.sum/A=B/": 20,
+	}, records.Map())
 
 }

sdk/metric/correct_test.go

@@ -365,7 +365,7 @@ func TestObserverCollection(t *testing.T) {
 		"float.updownsumobserver.sum/C=D/R=V": 1,
 		"int.updownsumobserver.sum//R=V":      -1,
 		"int.updownsumobserver.sum/A=B/R=V":   1,
-	}, out.Map)
+	}, out.Map())
 }
 
 func TestSumObserverInputRange(t *testing.T) {
@@ -468,7 +468,7 @@ func TestObserverBatch(t *testing.T) {
 		"float.valueobserver.lastvalue/C=D/R=V": -1,
 		"int.valueobserver.lastvalue//R=V":      1,
 		"int.valueobserver.lastvalue/A=B/R=V":   1,
-	}, out.Map)
+	}, out.Map())
 }
 
 func TestRecordBatch(t *testing.T) {
@@ -503,7 +503,7 @@ func TestRecordBatch(t *testing.T) {
 		"float64.sum/A=B,C=D/R=V":   2,
 		"int64.exact/A=B,C=D/R=V":   3,
 		"float64.exact/A=B,C=D/R=V": 4,
-	}, out.Map)
+	}, out.Map())
 }
 
 // TestRecordPersistence ensures that a direct-called instrument that
@@ -583,5 +583,5 @@ func TestSyncInAsync(t *testing.T) {
 	require.EqualValues(t, map[string]float64{
 		"counter.sum//R=V":        100,
 		"observer.lastvalue//R=V": 10,
-	}, out.Map)
+	}, out.Map())
 }

sdk/metric/processor/basic/basic.go

@@ -67,28 +67,29 @@ type (
 		// being maintained, taken from the process start time.
 		stateful bool
 
-		// TODO: as seen in lengthy comments below, both the
-		// `current` and `delta` fields have multiple uses
-		// depending on the specific configuration of
-		// instrument, exporter, and accumulator.  It is
-		// possible to simplify this situation by declaring
-		// explicit fields that are not used with a dual
-		// purpose.  Improve this situation?
-		//
-		// 1. "delta" is used to combine deltas from multiple
-		// accumulators, and it is also used to store the
-		// output of subtraction when computing deltas of
-		// PrecomputedSum instruments.
-		//
-		// 2. "current" either refers to the Aggregator passed
-		// to Process() by a single accumulator (when either
-		// there is just one Accumulator, or the instrument is
-		// Asynchronous), or it refers to "delta", depending
-		// on configuration.
-
-		current    export.Aggregator // refers to single-accumulator checkpoint or delta.
-		delta      export.Aggregator // owned if multi accumulator else nil.
-		cumulative export.Aggregator // owned if stateful else nil.
+		// currentOwned indicates that "current" was allocated
+		// by the processor in order to merge results from
+		// multiple Accuulators during a single collection
+		// round, which may happen either because:
+		// (1) multiple Accumulators output the same Metric
+		// (2) one Accumulator is configured with dimensionality reduction.
+		currentOwned bool
+
+		// current refers the output frmo a single Accumulator
+		// (if !currentOwned) or it refers to an Aggregator
+		// owned by the processor used to accumulate multiple
+		// values in a single collection round.
+		current export.Aggregator
+
+		// delta if non-nil refers to an Aggregator owned by
+		// the processor used to compute deltas between
+		// precomputed sums.
+		delta export.Aggregator
+
+		// cumulative if non-nil refers to an Aggregator owned
+		// by the processor used to store the last cumulative
+		// value.
+		cumulative export.Aggregator
 	}
 
 	state struct {
@@ -172,10 +173,8 @@ func (b *Processor) Process(accum export.Accumulation) error {
 				// If we know we need to compute deltas, allocate two aggregators.
 				b.AggregatorFor(desc, &newValue.cumulative, &newValue.delta)
 			} else {
-				// In this case we are not certain to need a delta, only allocate a
-				// cumulative aggregator.  We _may_ need a delta accumulator if
-				// multiple synchronous Accumulators produce an Accumulation (handled
-				// below), which requires merging them into a temporary Aggregator.
+				// In this case we are certain not to need a delta, only allocate
+				// a cumulative aggregator.
 				b.AggregatorFor(desc, &newValue.cumulative)
 			}
 		}
@@ -212,71 +211,39 @@ func (b *Processor) Process(accum export.Accumulation) error {
 	// Case (b) occurs when the variable `sameCollection` is true,
 	// indicating that the stateKey for Accumulation has already
 	// been seen in the same collection.  When this happens, it
-	// implies that multiple Accumulators are being used because
-	// the Accumulator outputs a maximum of one Accumulation per
-	// instrument and label set.
-	//
-	// The following logic distinguishes between asynchronous and
-	// synchronous instruments in order to ensure that the use of
-	// multiple Accumulators does not change instrument semantics.
-	// To maintain the instrument semantics, multiple synchronous
-	// Accumulations should be merged, whereas when multiple
-	// asynchronous Accumulations are processed, the last value
-	// should be kept.
+	// implies that multiple Accumulators are being used, or that
+	// a single Accumulator has been configured with a label key
+	// filter.
 
 	if !sameCollection {
-		// This is the first Accumulation we've seen for this
-		// stateKey during this collection.  Just keep a
-		// reference to the Accumulator's Aggregator.
-		value.current = agg
-		return nil
-	}
-	if desc.MetricKind().Asynchronous() {
-		// The last value across multiple accumulators is taken.
-		// Just keep a reference to the Accumulator's Aggregator.
-		value.current = agg
-		return nil
+		if !value.currentOwned {
+			// This is the first Accumulation we've seen
+			// for this stateKey during this collection.
+			// Just keep a reference to the Accumulator's
+			// Aggregator.
+			value.current = agg
+			return nil
+		}
+		return agg.SynchronizedMove(value.current, desc)
 	}
 
 	// The above two cases are keeping a reference to the
 	// Accumulator's Aggregator.  The remaining cases address
 	// synchronous instruments, which always merge multiple
 	// Accumulations using `value.delta` for temporary storage.
-
-	if value.delta == nil {
-		// The temporary `value.delta` may have been allocated
-		// already, either in a prior pass through this block of
-		// code or in the `!ok` branch above.  It would be
-		// allocated in the `!ok` branch if this is stateful
-		// PrecomputedSum instrument (in which case the exporter
-		// is requesting a delta so we allocate it up front),
-		// and it would be allocated in this block when multiple
-		// accumulators are used and the first condition is not
-		// met.
-		b.AggregatorSelector.AggregatorFor(desc, &value.delta)
-	}
-	if value.current != value.delta {
-		// If the current and delta Aggregators are not the same it
-		// implies that multiple Accumulators were used.  The first
-		// Accumulation seen for a given stateKey will return in
-		// one of the cases above after assigning `value.current
-		// = agg` (i.e., after taking a reference to the
-		// Accumulator's Aggregator).
-		//
-		// The second time through this branch copies the
-		// Accumulator's Aggregator into `value.delta` and sets
-		// `value.current` appropriately to avoid this branch if
-		// a third Accumulator is used.
-		err := value.current.SynchronizedMove(value.delta, desc)
-		if err != nil {
+	if !value.currentOwned {
+		tmp := value.current
+		b.AggregatorSelector.AggregatorFor(desc, &value.current)
+		value.currentOwned = true
+		if err := tmp.SynchronizedMove(value.current, desc); err != nil {
 			return err
 		}
-		value.current = value.delta
 	}
+
 	// The two statements above ensures that `value.current` refers
 	// to `value.delta` and not to an Accumulator's Aggregator.  Now
 	// combine this Accumulation with the prior Accumulation.
-	return value.delta.Merge(agg, desc)
+	return value.current.Merge(agg, desc)
 }
 
 // CheckpointSet returns the associated CheckpointSet.  Use the