trie, core/state: improve memory usage and performance (#3135)

* trie: store nodes as pointers

This avoids memory copies when unwrapping node interface values.

name      old time/op  new time/op  delta
Get        388ns ± 8%   215ns ± 2%  -44.56%  (p=0.000 n=15+15)
GetDB      363ns ± 3%   202ns ± 2%  -44.21%  (p=0.000 n=15+15)
UpdateBE  1.57µs ± 2%  1.29µs ± 3%  -17.80%  (p=0.000 n=13+15)
UpdateLE  1.92µs ± 2%  1.61µs ± 2%  -16.25%  (p=0.000 n=14+14)
HashBE    2.16µs ± 6%  2.18µs ± 6%     ~     (p=0.436 n=15+15)
HashLE    7.43µs ± 3%  7.21µs ± 3%   -2.96%  (p=0.000 n=15+13)

* trie: close temporary databases in GetDB benchmark

* trie: don't keep []byte from DB load around

Nodes decoded from a DB load kept hashes and values as sub-slices of
the DB value. This can be a problem because loading from leveldb often
returns []byte with a cap that's larger than necessary, increasing
memory usage.

* trie: unload old cached nodes

* trie, core/state: use cache unloading for account trie

* trie: use explicit private flags (fixes Go 1.5 reflection issue).

* trie: fixup cachegen overflow at request of nick

* core/state: rename journal size constant

1 files changed, 5 insertions, 5 deletions

diff --git a/trie/proof.go b/trie/proof.go
index 116c13a1b..f193b52df 100644
--- a/trie/proof.go
+++ b/trie/proof.go
@@ -44,7 +44,7 @@ func (t *Trie) Prove(key []byte) []rlp.RawValue {
 	tn := t.root
 	for len(key) > 0 && tn != nil {
 		switch n := tn.(type) {
-		case shortNode:
+		case *shortNode:
 			if len(key) < len(n.Key) || !bytes.Equal(n.Key, key[:len(n.Key)]) {
 				// The trie doesn't contain the key.
 				tn = nil
@@ -53,7 +53,7 @@ func (t *Trie) Prove(key []byte) []rlp.RawValue {
 				key = key[len(n.Key):]
 			}
 			nodes = append(nodes, n)
-		case fullNode:
+		case *fullNode:
 			tn = n.Children[key[0]]
 			key = key[1:]
 			nodes = append(nodes, n)
@@ -70,7 +70,7 @@ func (t *Trie) Prove(key []byte) []rlp.RawValue {
 			panic(fmt.Sprintf("%T: invalid node: %v", tn, tn))
 		}
 	}
-	hasher := newHasher()
+	hasher := newHasher(0, 0)
 	proof := make([]rlp.RawValue, 0, len(nodes))
 	for i, n := range nodes {
 		// Don't bother checking for errors here since hasher panics
@@ -130,13 +130,13 @@ func VerifyProof(rootHash common.Hash, key []byte, proof []rlp.RawValue) (value
 func get(tn node, key []byte) ([]byte, node) {
 	for len(key) > 0 {
 		switch n := tn.(type) {
-		case shortNode:
+		case *shortNode:
 			if len(key) < len(n.Key) || !bytes.Equal(n.Key, key[:len(n.Key)]) {
 				return nil, nil
 			}
 			tn = n.Val
 			key = key[len(n.Key):]
-		case fullNode:
+		case *fullNode:
 			tn = n.Children[key[0]]
 			key = key[1:]
 		case hashNode: