libs/db: bbolt (etcd's fork of bolt) (#3610)

Description:

    add boltdb implement for db interface.

    The boltdb is safe and high performence embedded KV database. It is based on B+tree and Mmap.
    Now it is maintained by etcd-io org. https://github.com/etcd-io/bbolt
    It is much better than LSM tree (levelDB) when RANDOM and SCAN read.

Replaced #3604
Refs #1835

Commits:

* add boltdb for storage

* update boltdb in gopkg.toml

* update bbolt in Gopkg.lock

* dep update  Gopkg.lock

* add boltdb'bucket when create Boltdb

* some modifies

* address my own comments

* fix most of the Iterator tests for boltdb

* bolt does not support concurrent writes while iterating

* add WARNING word

* note that ReadOnly option is not supported

* fixes after Ismail's review

Co-Authored-By: melekes <anton.kalyaev@gmail.com>

* panic if View returns error

plus specify bucket in the top comment

libs/db/common_test.go

@@ -1,6 +1,8 @@
 package db
 
 import (
+	"bytes"
+	"encoding/binary"
 	"fmt"
 	"io/ioutil"
 	"sync"
@@ -8,6 +10,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	cmn "github.com/tendermint/tendermint/libs/common"
 )
 
 //----------------------------------------
@@ -188,3 +191,66 @@ func (mockIterator) Value() []byte {
 
 func (mockIterator) Close() {
 }
+
+func benchmarkRandomReadsWrites(b *testing.B, db DB) {
+	b.StopTimer()
+
+	// create dummy data
+	const numItems = int64(1000000)
+	internal := map[int64]int64{}
+	for i := 0; i < int(numItems); i++ {
+		internal[int64(i)] = int64(0)
+	}
+
+	// fmt.Println("ok, starting")
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		// Write something
+		{
+			idx := int64(cmn.RandInt()) % numItems
+			internal[idx]++
+			val := internal[idx]
+			idxBytes := int642Bytes(int64(idx))
+			valBytes := int642Bytes(int64(val))
+			//fmt.Printf("Set %X -> %X\n", idxBytes, valBytes)
+			db.Set(idxBytes, valBytes)
+		}
+
+		// Read something
+		{
+			idx := int64(cmn.RandInt()) % numItems
+			valExp := internal[idx]
+			idxBytes := int642Bytes(int64(idx))
+			valBytes := db.Get(idxBytes)
+			//fmt.Printf("Get %X -> %X\n", idxBytes, valBytes)
+			if valExp == 0 {
+				if !bytes.Equal(valBytes, nil) {
+					b.Errorf("Expected %v for %v, got %X", nil, idx, valBytes)
+					break
+				}
+			} else {
+				if len(valBytes) != 8 {
+					b.Errorf("Expected length 8 for %v, got %X", idx, valBytes)
+					break
+				}
+				valGot := bytes2Int64(valBytes)
+				if valExp != valGot {
+					b.Errorf("Expected %v for %v, got %v", valExp, idx, valGot)
+					break
+				}
+			}
+		}
+
+	}
+}
+
+func int642Bytes(i int64) []byte {
+	buf := make([]byte, 8)
+	binary.BigEndian.PutUint64(buf, uint64(i))
+	return buf
+}
+
+func bytes2Int64(buf []byte) int64 {
+	return int64(binary.BigEndian.Uint64(buf))
+}