batch: add option for executing requests immediately

We make the default non-lazy, and will make the incoming gossip requests
lazy.

batch/interface.go

@@ -25,6 +25,23 @@ type Request struct {
 	//
 	// NOTE: This field is optional.
 	OnCommit func(commitErr error) error
+
+	// lazy should be true if we don't have to immediately execute this
+	// request when it comes in. This means that it can be scheduled later,
+	// allowing larger batches.
+	lazy bool
+}
+
+// SchedulerOption is a type that can be used to supply options to a scheduled
+// request.
+type SchedulerOption func(r *Request)
+
+// LazyAdd will make the request be executed lazily, added to the next batch to
+// reduce db contention.
+func LazyAdd() SchedulerOption {
+	return func(r *Request) {
+		r.lazy = true
+	}
 }
 
 // Scheduler abstracts a generic batching engine that accumulates an incoming
@@ -32,7 +49,7 @@ type Request struct {
 type Scheduler interface {
 	// Execute schedules a Request for execution with the next available
 	// batch. This method blocks until the the underlying closure has been
-	// run against the databse. The resulting error is returned to the
+	// run against the database. The resulting error is returned to the
 	// caller.
 	Execute(req *Request) error
 }

batch/scheduler.go

@@ -60,6 +60,12 @@ func (s *TimeScheduler) Execute(r *Request) error {
 		time.AfterFunc(s.duration, s.b.trigger)
 	}
 	s.b.reqs = append(s.b.reqs, &req)
+
+	// If this is a non-lazy request, we'll execute the batch immediately.
+	if !r.lazy {
+		go s.b.trigger()
+	}
+
 	s.mu.Unlock()
 
 	// Wait for the batch to process the request. If the batch didn't