diff --git a/tsdb/engine/tsm1/log.go b/tsdb/engine/tsm1/log.go
index c4cff15dc1..46b059a50f 100644
--- a/tsdb/engine/tsm1/log.go
+++ b/tsdb/engine/tsm1/log.go
@@ -33,6 +33,8 @@ const (
 	idleFlush
 	// startupFlush indicates that we're flushing because the database is starting up
 	startupFlush
+
+	writeBufLen = 32 << 10
 )
 
 const (
diff --git a/tsdb/engine/tsm1/wal.go b/tsdb/engine/tsm1/wal.go
index 67bb18cf3d..bb352056eb 100644
--- a/tsdb/engine/tsm1/wal.go
+++ b/tsdb/engine/tsm1/wal.go
@@ -25,7 +25,7 @@ const (
 
 	WALFilePrefix = "_"
 
-	writeBufLen = 128 << 10 // 128kb
+	defaultBufLen = 1024 << 10 // 1MB (sized for batches of 5000 points)
 )
 
 // walEntry is a byte written to a wal segment file that indicates what the following compressed block contains
@@ -101,9 +101,6 @@ func (l *WAL) Open() error {
 }
 
 func (l *WAL) WritePoints(points []models.Point) error {
-	l.mu.Lock()
-	defer l.mu.Unlock()
-
 	entry := &WriteWALEntry{
 		Points: points,
 	}
@@ -142,6 +139,8 @@ func (l *WAL) ClosedSegments() ([]string, error) {
 }
 
 func (l *WAL) writeToLog(entry WALEntry) error {
+	l.mu.RLock()
+	defer l.mu.RUnlock()
 	// Make sure the log has not been closed
 	select {
 	case <-l.closing:
@@ -165,9 +164,6 @@ func (l *WAL) writeToLog(entry WALEntry) error {
 }
 
 func (l *WAL) Delete(keys []string) error {
-	l.mu.Lock()
-	defer l.mu.Unlock()
-
 	entry := &DeleteWALEntry{
 		Keys: keys,
 	}
@@ -228,7 +224,7 @@ type WALEntry interface {
 	Type() walEntryType
 	Encode(dst []byte) ([]byte, error)
 	MarshalBinary() ([]byte, error)
-	UnmarshlBinary(b []byte) error
+	UnmarshalBinary(b []byte) error
 }
 
 // WriteWALEntry represents a write of points.
@@ -248,7 +244,7 @@ func (w *WriteWALEntry) Encode(dst []byte) ([]byte, error) {
 		// Make sure we have enough space in our buf before copying.  If not,
 		// grow the buf.
 		if len(bytes)+4 > len(dst)-n {
-			grow := make([]byte, writeBufLen)
+			grow := make([]byte, len(bytes)*2)
 			dst = append(dst, grow...)
 		}
 		n += copy(dst[n:], u32tob(uint32(len(bytes))))
@@ -260,11 +256,11 @@ func (w *WriteWALEntry) Encode(dst []byte) ([]byte, error) {
 
 func (w *WriteWALEntry) MarshalBinary() ([]byte, error) {
 	// Temp buffer to write marshaled points into
-	b := make([]byte, writeBufLen)
+	b := make([]byte, defaultBufLen)
 	return w.Encode(b)
 }
 
-func (w *WriteWALEntry) UnmarshlBinary(b []byte) error {
+func (w *WriteWALEntry) UnmarshalBinary(b []byte) error {
 	var i int
 
 	for i < len(b) {
@@ -291,11 +287,11 @@ type DeleteWALEntry struct {
 }
 
 func (w *DeleteWALEntry) MarshalBinary() ([]byte, error) {
-	b := make([]byte, writeBufLen)
+	b := make([]byte, defaultBufLen)
 	return w.Encode(b)
 }
 
-func (w *DeleteWALEntry) UnmarshlBinary(b []byte) error {
+func (w *DeleteWALEntry) UnmarshalBinary(b []byte) error {
 	w.Keys = strings.Split(string(b), "\n")
 	return nil
 }
@@ -304,7 +300,7 @@ func (w *DeleteWALEntry) Encode(dst []byte) ([]byte, error) {
 	var n int
 	for _, k := range w.Keys {
 		if len(dst)+1 > len(dst)-n {
-			grow := make([]byte, writeBufLen)
+			grow := make([]byte, defaultBufLen)
 			dst = append(dst, grow...)
 		}
 
@@ -325,13 +321,11 @@ func (w *DeleteWALEntry) Type() walEntryType {
 type WALSegmentWriter struct {
 	w    io.WriteCloser
 	size int
-	b    []byte
 }
 
 func NewWALSegmentWriter(w io.WriteCloser) *WALSegmentWriter {
 	return &WALSegmentWriter{
 		w: w,
-		b: make([]byte, writeBufLen),
 	}
 }
 
@@ -343,7 +337,7 @@ func (w *WALSegmentWriter) Path() string {
 }
 
 func (w *WALSegmentWriter) Write(e WALEntry) error {
-	bytes := getBuf(writeBufLen)
+	bytes := getBuf(defaultBufLen)
 	defer putBuf(bytes)
 
 	b, err := e.Encode(bytes)
@@ -351,25 +345,19 @@ func (w *WALSegmentWriter) Write(e WALEntry) error {
 		return err
 	}
 
-	// Temp buf for snappy compression
-	cb := getBuf(len(b))
-	defer putBuf(cb)
+	compressed := snappy.Encode(b, b)
 
-	compressed := snappy.Encode(cb, b)
-
-	// Temp buf for file writing
-	wb := getBuf(len(compressed) + 5)
-	defer putBuf(wb)
-
-	n := copy(wb, []byte{byte(e.Type())})
-	n += copy(wb[n:], u32tob(uint32(len(compressed))))
-	n += copy(wb[n:], compressed)
-
-	if _, err := w.w.Write(wb[:n]); err != nil {
-		return fmt.Errorf("error writing to WAL: %v", err)
+	if _, err := w.w.Write([]byte{byte(e.Type())}); err != nil {
+		return err
+	}
+	if _, err := w.w.Write(u32tob(uint32(len(compressed)))); err != nil {
+		return err
+	}
+	if _, err := w.w.Write(compressed); err != nil {
+		return err
 	}
 
-	w.size += n
+	w.size += len(compressed) + 5
 
 	return nil
 }
@@ -405,7 +393,7 @@ func NewWALSegmentReader(r io.ReadCloser) *WALSegmentReader {
 
 // Next indicates if there is a value to read
 func (r *WALSegmentReader) Next() bool {
-	b := getBuf(writeBufLen)
+	b := getBuf(defaultBufLen)
 	defer putBuf(b)
 
 	// read the type and the length of the entry
@@ -440,7 +428,7 @@ func (r *WALSegmentReader) Next() bool {
 		return true
 	}
 
-	buf := getBuf(writeBufLen)
+	buf := getBuf(defaultBufLen)
 	defer putBuf(buf)
 
 	data, err := snappy.Decode(buf, b[:length])
@@ -459,7 +447,7 @@ func (r *WALSegmentReader) Next() bool {
 		r.err = fmt.Errorf("unknown wal entry type: %v", entryType)
 		return true
 	}
-	r.err = r.entry.UnmarshlBinary(data)
+	r.err = r.entry.UnmarshalBinary(data)
 
 	return true
 }