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, 58 insertions, 0 deletions

diff --git a/trie/node_test.go b/trie/node_test.go
new file mode 100644
index 000000000..7ad1ff9e7
--- /dev/null
+++ b/trie/node_test.go
@@ -0,0 +1,58 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package trie
+
+import "testing"
+
+func TestCanUnload(t *testing.T) {
+	tests := []struct {
+		flag                 nodeFlag
+		cachegen, cachelimit uint16
+		want                 bool
+	}{
+		{
+			flag: nodeFlag{dirty: true, gen: 0},
+			want: false,
+		},
+		{
+			flag:     nodeFlag{dirty: false, gen: 0},
+			cachegen: 0, cachelimit: 0,
+			want: true,
+		},
+		{
+			flag:     nodeFlag{dirty: false, gen: 65534},
+			cachegen: 65535, cachelimit: 1,
+			want: true,
+		},
+		{
+			flag:     nodeFlag{dirty: false, gen: 65534},
+			cachegen: 0, cachelimit: 1,
+			want: true,
+		},
+		{
+			flag:     nodeFlag{dirty: false, gen: 1},
+			cachegen: 65535, cachelimit: 1,
+			want: true,
+		},
+	}
+
+	for _, test := range tests {
+		if got := test.flag.canUnload(test.cachegen, test.cachelimit); got != test.want {
+			t.Errorf("%+v\n   got %t, want %t", test, got, test.want)
+		}
+	}
+}