reuse node repo merge buffers

fix format


missing close call

claimtrie/node/manager.go

@@ -77,6 +77,7 @@ func (nc *nodeCache) Delete(key string) {
 	existing := nc.elements[key]
 	if existing != nil {
 		delete(nc.elements, key)
+		existing.Value.(nodeCacheLeaf).node.Close()
 		nc.data.Remove(existing)
 	}
 }

claimtrie/node/noderepo/pebble.go

@@ -2,7 +2,9 @@ package noderepo
 
 import (
 	"bytes"
+	"io"
 	"sort"
+	"sync"
 
 	"github.com/btcsuite/btcd/claimtrie/change"
 	"github.com/cockroachdb/pebble"
@@ -13,9 +15,67 @@ type Pebble struct {
 	db *pebble.DB
 }
 
+type pooledMerger struct {
+	pool   *sync.Pool
+	buffer []byte
+}
+
+func (a *pooledMerger) MergeNewer(value []byte) error {
+	if a.buffer == nil {
+		a.buffer = a.pool.Get().([]byte)
+	}
+	a.buffer = append(a.buffer, value...)
+	return nil
+}
+func (a *pooledMerger) MergeOlder(value []byte) error {
+	if a.buffer == nil {
+		a.buffer = a.pool.Get().([]byte)
+	}
+	n := len(a.buffer)
+	if cap(a.buffer) >= len(value)+n {
+		a.buffer = a.buffer[0 : len(value)+n]      // expand it
+		copy(a.buffer[len(value):], a.buffer[0:n]) // could overlap
+		copy(a.buffer, value)
+	} else {
+		existing := a.buffer
+		a.buffer = make([]byte, 0, len(value)+len(existing))
+		a.buffer = append(a.buffer, value...)
+		a.buffer = append(a.buffer, existing...)
+	}
+	return nil
+}
+
+func (a *pooledMerger) Finish(_ bool) ([]byte, io.Closer, error) {
+	return a.buffer, a, nil
+}
+
+func (a *pooledMerger) Close() error {
+	a.pool.Put(a.buffer[:0])
+	a.buffer = nil
+	a.pool = nil
+	return nil
+}
+
 func NewPebble(path string) (*Pebble, error) {
 
-	db, err := pebble.Open(path, &pebble.Options{Cache: pebble.NewCache(32 << 20), BytesPerSync: 4 << 20})
+	mp := &sync.Pool{
+		New: func() interface{} {
+			return make([]byte, 0, 256)
+		},
+	}
+
+	db, err := pebble.Open(path, &pebble.Options{
+		Merger: &pebble.Merger{
+			Merge: func(key, value []byte) (pebble.ValueMerger, error) {
+				p := &pooledMerger{pool: mp}
+				return p, p.MergeNewer(value)
+			},
+			Name: pebble.DefaultMerger.Name, // yes, it's a lie
+		},
+		Cache:        pebble.NewCache(32 << 20),
+		BytesPerSync: 4 << 20,
+	})
+
 	repo := &Pebble{db: db}
 
 	return repo, errors.Wrapf(err, "unable to open %s", path)
@@ -36,6 +96,7 @@ func (repo *Pebble) AppendChanges(changes []change.Change) error {
 			return errors.Wrap(err, "in marshaller")
 		}
 
+		// expecting this next line to make a copy of the buffer, not hold it
 		err = batch.Merge(chg.Name, buffer.Bytes(), pebble.NoSync)
 		if err != nil {
 			return errors.Wrap(err, "in merge")