Switch WAL byte pools to sync/pool

The current bytes.Pool will hold onto byte slices indefinitely. Large
writes can cause the pool to hold onto very large buffers over time.
Testing w/ sync/pool seems to perform similarly now so using a sync/pool
will allow these buffers to be GC'd when necessary.

tsdb/engine/tsm1/pools.go

@@ -1,15 +1,26 @@
 package tsm1
 
-import "github.com/influxdata/influxdb/pkg/pool"
+import "sync"
 
-var bufPool = pool.NewBytes(10)
+var bufPool sync.Pool
 
 // getBuf returns a buffer with length size from the buffer pool.
-func getBuf(size int) []byte {
-	return bufPool.Get(size)
+func getBuf(size int) *[]byte {
+	x := bufPool.Get()
+	if x == nil {
+		b := make([]byte, size)
+		return &b
+	}
+	buf := x.(*[]byte)
+	if cap(*buf) < size {
+		b := make([]byte, size)
+		return &b
+	}
+	*buf = (*buf)[:size]
+	return buf
 }
 
 // putBuf returns a buffer to the pool.
-func putBuf(buf []byte) {
+func putBuf(buf *[]byte) {
 	bufPool.Put(buf)
 }

tsdb/engine/tsm1/wal.go

@@ -382,16 +382,16 @@ func (l *WAL) writeToLog(entry WALEntry) (int, error) {
 	//defer l.limiter.Release()
 
 	// encode and compress the entry while we're not locked
-	bytes := getBuf(walEncodeBufSize)
-	defer putBuf(bytes)
+	bytes := *(getBuf(walEncodeBufSize))
+	defer putBuf(&bytes)
 
 	b, err := entry.Encode(bytes)
 	if err != nil {
 		return -1, err
 	}
 
-	encBuf := getBuf(snappy.MaxEncodedLen(len(b)))
-	defer putBuf(encBuf)
+	encBuf := *(getBuf(snappy.MaxEncodedLen(len(b))))
+	defer putBuf(&encBuf)
 	compressed := snappy.Encode(encBuf, b)
 	syncErr := make(chan error)
 
@@ -1031,8 +1031,8 @@ func NewWALSegmentReader(r io.ReadCloser) *WALSegmentReader {
 
 // Next indicates if there is a value to read.
 func (r *WALSegmentReader) Next() bool {
-	b := getBuf(defaultBufLen)
-	defer putBuf(b)
+	b := *(getBuf(defaultBufLen))
+	defer putBuf(&b)
 	var nReadOK int
 
 	// read the type and the length of the entry
@@ -1069,8 +1069,8 @@ func (r *WALSegmentReader) Next() bool {
 		r.err = err
 		return true
 	}
-	decBuf := getBuf(decLen)
-	defer putBuf(decBuf)
+	decBuf := *(getBuf(decLen))
+	defer putBuf(&decBuf)
 
 	data, err := snappy.Decode(decBuf, b[:length])
 	if err != nil {