add in support for batched writes

implement batch ops for different datastore types

rename Transaction to Batch

Revert "add in support for batched writes"

add in benchmarks for put and batchput

move batching into separate interface

address concerns from PR

regrab old code

measure.go

@@ -148,6 +148,85 @@ func (m *measure) Query(q query.Query) (query.Results, error) {
 	return res, err
 }
 
+type measuredBatch struct {
+	puts    int
+	deletes int
+
+	putts datastore.Batch
+	delts datastore.Batch
+
+	m *measure
+}
+
+func (m *measure) Batch() (datastore.Batch, error) {
+	bds, ok := m.backend.(datastore.BatchingDatastore)
+	if !ok {
+		return nil, datastore.ErrBatchUnsupported
+	}
+	pb, err := bds.Batch()
+	if err != nil {
+		return nil, err
+	}
+
+	db, err := bds.Batch()
+	if err != nil {
+		return nil, err
+	}
+
+	return &measuredBatch{
+		putts: pb,
+		delts: db,
+
+		m: m,
+	}, nil
+}
+
+func (mt *measuredBatch) Put(key datastore.Key, val interface{}) error {
+	mt.puts++
+	valb, ok := val.([]byte)
+	if !ok {
+		return datastore.ErrInvalidType
+	}
+	_ = mt.m.putSize.RecordValue(int64(len(valb)))
+	return mt.putts.Put(key, val)
+}
+
+func (mt *measuredBatch) Delete(key datastore.Key) error {
+	mt.deletes++
+	return mt.delts.Delete(key)
+}
+
+func (mt *measuredBatch) Commit() error {
+	err := logBatchCommit(mt.delts, mt.deletes, mt.m.deleteNum, mt.m.deleteErr, mt.m.deleteLatency)
+	if err != nil {
+		return err
+	}
+
+	err = logBatchCommit(mt.putts, mt.puts, mt.m.putNum, mt.m.putErr, mt.m.putLatency)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func logBatchCommit(b datastore.Batch, n int, num, errs metrics.Counter, lat *metrics.Histogram) error {
+	if n > 0 {
+		before := time.Now()
+		err := b.Commit()
+		took := int(time.Now().Sub(before)/time.Microsecond) / n
+		num.AddN(uint64(n))
+		for i := 0; i < n; i++ {
+			_ = lat.RecordValue(int64(took))
+		}
+		if err != nil {
+			errs.Add()
+			return err
+		}
+	}
+	return nil
+}
+
 func (m *measure) Close() error {
 	m.putNum.Remove()
 	m.putErr.Remove()