Export a metric of total number of leaves fetched (#2023)

CHANGELOG.md

@@ -24,6 +24,10 @@ tolerate 2 nodes being unavailable, instead of just 1).
 A potential deadlock condition in the log sequencer when the process is
 attempting to exit has been addressed.
 
+#### Monitoring & Metrics
+A count of the total number of individual leaves the logserver attempts to
+fetch via the GetEntries.\* API methods has been added.
+
 ### Map Changes
 
 The verifiable map is still experimental. APIs, such as SetLeaves, have been

server/log_rpc_server.go

@@ -50,6 +50,7 @@ type TrillianLogRPCServer struct {
 	timeSource            clock.TimeSource
 	leafCounter           monitoring.Counter
 	proofIndexPercentiles monitoring.Histogram
+	fetchedLeaves         monitoring.Counter
 }
 
 // NewTrillianLogRPCServer creates a new RPC server backed by a LogStorageProvider.
@@ -71,6 +72,10 @@ func NewTrillianLogRPCServer(registry extension.Registry, timeSource clock.TimeS
 			"Count of inclusion proof request index using percentage of current log size at the time",
 			monitoring.PercentileBuckets(1),
 		),
+		fetchedLeaves: mf.NewCounter(
+			"fetched_leaves",
+			"Count of individual leaves fetched through get-entries calls",
+		),
 	}
 }
 
@@ -500,6 +505,7 @@ func (t *TrillianLogRPCServer) GetLeavesByIndex(ctx context.Context, req *trilli
 	}
 	defer t.closeAndLog(ctx, tree.TreeId, tx, "GetLeavesByIndex")
 
+	t.fetchedLeaves.Add(float64(len(req.LeafIndex)))
 	leaves, err := tx.GetLeavesByIndex(ctx, req.LeafIndex)
 	if err != nil {
 		return nil, err
@@ -553,6 +559,7 @@ func (t *TrillianLogRPCServer) GetLeavesByRange(ctx context.Context, req *trilli
 	r := &trillian.GetLeavesByRangeResponse{SignedLogRoot: slr}
 
 	if req.StartIndex < int64(root.TreeSize) {
+		t.fetchedLeaves.Add(float64(req.Count))
 		leaves, err := tx.GetLeavesByRange(ctx, req.StartIndex, req.Count)
 		if err != nil {
 			return nil, err
@@ -589,6 +596,7 @@ func (t *TrillianLogRPCServer) GetLeavesByHash(ctx context.Context, req *trillia
 	}
 	defer t.closeAndLog(ctx, tree.TreeId, tx, "GetLeavesByHash")
 
+	t.fetchedLeaves.Add(float64(len(req.LeafHash)))
 	leaves, err := tx.GetLeavesByHash(ctx, req.LeafHash, req.OrderBySequence)
 	if err != nil {
 		return nil, err

server/log_rpc_server_test.go

@@ -425,6 +425,10 @@ func TestGetLeavesByRange(t *testing.T) {
 		if got := rsp.Leaves; !cmp.Equal(got, test.want, cmp.Comparer(proto.Equal)) {
 			t.Errorf("GetLeavesByRange(%d, %+d)=%+v; want %+v", req.StartIndex, req.Count, got, test.want)
 		}
+
+		if gotCount, wantCount := server.fetchedLeaves.Value(), float64(test.count); gotCount != wantCount {
+			t.Errorf("GetLeavesByRange() incremented fetched count by %f,  want %f", gotCount, wantCount)
+		}
 	}
 }