database.go

// Copyright 2018 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 (
	"errors"
	"fmt"
	"io"
	"reflect"
	"runtime"
	"sync"
	"time"

	"github.com/VictoriaMetrics/fastcache"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/rlp"
)

var (
	memcacheCleanHitMeter   = metrics.NewRegisteredMeter("trie/memcache/clean/hit", nil)
	memcacheCleanMissMeter  = metrics.NewRegisteredMeter("trie/memcache/clean/miss", nil)
	memcacheCleanReadMeter  = metrics.NewRegisteredMeter("trie/memcache/clean/read", nil)
	memcacheCleanWriteMeter = metrics.NewRegisteredMeter("trie/memcache/clean/write", nil)

	memcacheDirtyHitMeter   = metrics.NewRegisteredMeter("trie/memcache/dirty/hit", nil)
	memcacheDirtyMissMeter  = metrics.NewRegisteredMeter("trie/memcache/dirty/miss", nil)
	memcacheDirtyReadMeter  = metrics.NewRegisteredMeter("trie/memcache/dirty/read", nil)
	memcacheDirtyWriteMeter = metrics.NewRegisteredMeter("trie/memcache/dirty/write", nil)

	memcacheFlushTimeTimer  = metrics.NewRegisteredResettingTimer("trie/memcache/flush/time", nil)
	memcacheFlushNodesMeter = metrics.NewRegisteredMeter("trie/memcache/flush/nodes", nil)
	memcacheFlushSizeMeter  = metrics.NewRegisteredMeter("trie/memcache/flush/size", nil)

	memcacheGCTimeTimer  = metrics.NewRegisteredResettingTimer("trie/memcache/gc/time", nil)
	memcacheGCNodesMeter = metrics.NewRegisteredMeter("trie/memcache/gc/nodes", nil)
	memcacheGCSizeMeter  = metrics.NewRegisteredMeter("trie/memcache/gc/size", nil)

	memcacheCommitTimeTimer  = metrics.NewRegisteredResettingTimer("trie/memcache/commit/time", nil)
	memcacheCommitNodesMeter = metrics.NewRegisteredMeter("trie/memcache/commit/nodes", nil)
	memcacheCommitSizeMeter  = metrics.NewRegisteredMeter("trie/memcache/commit/size", nil)
)

// Database is an intermediate write layer between the trie data structures and
// the disk database. The aim is to accumulate trie writes in-memory and only
// periodically flush a couple tries to disk, garbage collecting the remainder.
//
// Note, the trie Database is **not** thread safe in its mutations, but it **is**
// thread safe in providing individual, independent node access. The rationale
// behind this split design is to provide read access to RPC handlers and sync
// servers even while the trie is executing expensive garbage collection.
type Database struct {
	diskdb ethdb.KeyValueStore // Persistent storage for matured trie nodes

	cleans  *fastcache.Cache            // GC friendly memory cache of clean node RLPs
	dirties map[common.Hash]*cachedNode // Data and references relationships of dirty trie nodes
	oldest  common.Hash                 // Oldest tracked node, flush-list head
	newest  common.Hash                 // Newest tracked node, flush-list tail

	gctime  time.Duration      // Time spent on garbage collection since last commit
	gcnodes uint64             // Nodes garbage collected since last commit
	gcsize  common.StorageSize // Data storage garbage collected since last commit

	flushtime  time.Duration      // Time spent on data flushing since last commit
	flushnodes uint64             // Nodes flushed since last commit
	flushsize  common.StorageSize // Data storage flushed since last commit

	dirtiesSize  common.StorageSize // Storage size of the dirty node cache (exc. metadata)
	childrenSize common.StorageSize // Storage size of the external children tracking
	preimages    *preimageStore     // The store for caching preimages

	lock sync.RWMutex
}

// rawNode is a simple binary blob used to differentiate between collapsed trie
// nodes and already encoded RLP binary blobs (while at the same time store them
// in the same cache fields).
type rawNode []byte

func (n rawNode) cache() (hashNode, bool)   { panic("this should never end up in a live trie") }
func (n rawNode) fstring(ind string) string { panic("this should never end up in a live trie") }

func (n rawNode) EncodeRLP(w io.Writer) error {
	_, err := w.Write(n)
	return err
}

// rawFullNode represents only the useful data content of a full node, with the
// caches and flags stripped out to minimize its data storage. This type honors
// the same RLP encoding as the original parent.
type rawFullNode [17]node

func (n rawFullNode) cache() (hashNode, bool)   { panic("this should never end up in a live trie") }
func (n rawFullNode) fstring(ind string) string { panic("this should never end up in a live trie") }

func (n rawFullNode) EncodeRLP(w io.Writer) error {
	eb := rlp.NewEncoderBuffer(w)
	n.encode(eb)
	return eb.Flush()
}

// rawShortNode represents only the useful data content of a short node, with the
// caches and flags stripped out to minimize its data storage. This type honors
// the same RLP encoding as the original parent.
type rawShortNode struct {
	Key []byte
	Val node
}

func (n rawShortNode) cache() (hashNode, bool)   { panic("this should never end up in a live trie") }
func (n rawShortNode) fstring(ind string) string { panic("this should never end up in a live trie") }

// cachedNode is all the information we know about a single cached trie node
// in the memory database write layer.
type cachedNode struct {
	node node   // Cached collapsed trie node, or raw rlp data
	size uint16 // Byte size of the useful cached data

	parents  uint32                 // Number of live nodes referencing this one
	children map[common.Hash]uint16 // External children referenced by this node

	flushPrev common.Hash // Previous node in the flush-list
	flushNext common.Hash // Next node in the flush-list
}

// cachedNodeSize is the raw size of a cachedNode data structure without any
// node data included. It's an approximate size, but should be a lot better
// than not counting them.
var cachedNodeSize = int(reflect.TypeOf(cachedNode{}).Size())

// cachedNodeChildrenSize is the raw size of an initialized but empty external
// reference map.
const cachedNodeChildrenSize = 48

// rlp returns the raw rlp encoded blob of the cached trie node, either directly
// from the cache, or by regenerating it from the collapsed node.
func (n *cachedNode) rlp() []byte {
	if node, ok := n.node.(rawNode); ok {
		return node
	}
	return nodeToBytes(n.node)
}

// obj returns the decoded and expanded trie node, either directly from the cache,
// or by regenerating it from the rlp encoded blob.
func (n *cachedNode) obj(hash common.Hash) node {
	if node, ok := n.node.(rawNode); ok {
		// The raw-blob format nodes are loaded either from the
		// clean cache or the database, they are all in their own
		// copy and safe to use unsafe decoder.
		return mustDecodeNodeUnsafe(hash[:], node)
	}
	return expandNode(hash[:], n.node)
}

// forChilds invokes the callback for all the tracked children of this node,
// both the implicit ones from inside the node as well as the explicit ones
// from outside the node.
func (n *cachedNode) forChilds(onChild func(hash common.Hash)) {
	for child := range n.children {
		onChild(child)
	}
	if _, ok := n.node.(rawNode); !ok {
		forGatherChildren(n.node, onChild)
	}
}

// forGatherChildren traverses the node hierarchy of a collapsed storage node and
// invokes the callback for all the hashnode children.
func forGatherChildren(n node, onChild func(hash common.Hash)) {
	switch n := n.(type) {
	case *rawShortNode:
		forGatherChildren(n.Val, onChild)
	case rawFullNode:
		for i := 0; i < 16; i++ {
			forGatherChildren(n[i], onChild)
		}
	case hashNode:
		onChild(common.BytesToHash(n))
	case valueNode, nil, rawNode:
	default:
		panic(fmt.Sprintf("unknown node type: %T", n))
	}
}

// simplifyNode traverses the hierarchy of an expanded memory node and discards
// all the internal caches, returning a node that only contains the raw data.
func simplifyNode(n node) node {
	switch n := n.(type) {
	case *shortNode:
		// Short nodes discard the flags and cascade
		return &rawShortNode{Key: n.Key, Val: simplifyNode(n.Val)}

	case *fullNode:
		// Full nodes discard the flags and cascade
		node := rawFullNode(n.Children)
		for i := 0; i < len(node); i++ {
			if node[i] != nil {
				node[i] = simplifyNode(node[i])
			}
		}
		return node

	case valueNode, hashNode, rawNode:
		return n

	default:
		panic(fmt.Sprintf("unknown node type: %T", n))
	}
}

// expandNode traverses the node hierarchy of a collapsed storage node and converts
// all fields and keys into expanded memory form.
func expandNode(hash hashNode, n node) node {
	switch n := n.(type) {
	case *rawShortNode:
		// Short nodes need key and child expansion
		return &shortNode{
			Key: compactToHex(n.Key),
			Val: expandNode(nil, n.Val),
			flags: nodeFlag{
				hash: hash,
			},
		}

	case rawFullNode:
		// Full nodes need child expansion
		node := &fullNode{
			flags: nodeFlag{
				hash: hash,
			},
		}
		for i := 0; i < len(node.Children); i++ {
			if n[i] != nil {
				node.Children[i] = expandNode(nil, n[i])
			}
		}
		return node

	case valueNode, hashNode:
		return n

	default:
		panic(fmt.Sprintf("unknown node type: %T", n))
	}
}

// Config defines all necessary options for database.
type Config struct {
	Cache     int    // Memory allowance (MB) to use for caching trie nodes in memory
	Journal   string // Journal of clean cache to survive node restarts
	Preimages bool   // Flag whether the preimage of trie key is recorded
}

// NewDatabase creates a new trie database to store ephemeral trie content before
// its written out to disk or garbage collected. No read cache is created, so all
// data retrievals will hit the underlying disk database.
func NewDatabase(diskdb ethdb.KeyValueStore) *Database {
	return NewDatabaseWithConfig(diskdb, nil)
}

// NewDatabaseWithConfig creates a new trie database to store ephemeral trie content
// before its written out to disk or garbage collected. It also acts as a read cache
// for nodes loaded from disk.
func NewDatabaseWithConfig(diskdb ethdb.KeyValueStore, config *Config) *Database {
	var cleans *fastcache.Cache
	if config != nil && config.Cache > 0 {
		if config.Journal == "" {
			cleans = fastcache.New(config.Cache * 1024 * 1024)
		} else {
			cleans = fastcache.LoadFromFileOrNew(config.Journal, config.Cache*1024*1024)
		}
	}
	var preimage *preimageStore
	if config != nil && config.Preimages {
		preimage = newPreimageStore(diskdb)
	}
	db := &Database{
		diskdb: diskdb,
		cleans: cleans,
		dirties: map[common.Hash]*cachedNode{{}: {
			children: make(map[common.Hash]uint16),
		}},
		preimages: preimage,
	}
	return db
}

// insert inserts a simplified trie node into the memory database.
// All nodes inserted by this function will be reference tracked
// and in theory should only used for **trie nodes** insertion.
func (db *Database) insert(hash common.Hash, size int, node node) {
	// If the node's already cached, skip
	if _, ok := db.dirties[hash]; ok {
		return
	}
	memcacheDirtyWriteMeter.Mark(int64(size))

	// Create the cached entry for this node
	entry := &cachedNode{
		node:      node,
		size:      uint16(size),
		flushPrev: db.newest,
	}
	entry.forChilds(func(child common.Hash) {
		if c := db.dirties[child]; c != nil {
			c.parents++
		}
	})
	db.dirties[hash] = entry

	// Update the flush-list endpoints
	if db.oldest == (common.Hash{}) {
		db.oldest, db.newest = hash, hash
	} else {
		db.dirties[db.newest].flushNext, db.newest = hash, hash
	}
	db.dirtiesSize += common.StorageSize(common.HashLength + entry.size)
}

// node retrieves a cached trie node from memory, or returns nil if none can be
// found in the memory cache.
func (db *Database) node(hash common.Hash) node {
	// Retrieve the node from the clean cache if available
	if db.cleans != nil {
		if enc := db.cleans.Get(nil, hash[:]); enc != nil {
			memcacheCleanHitMeter.Mark(1)
			memcacheCleanReadMeter.Mark(int64(len(enc)))

			// The returned value from cache is in its own copy,
			// safe to use mustDecodeNodeUnsafe for decoding.
			return mustDecodeNodeUnsafe(hash[:], enc)
		}
	}
	// Retrieve the node from the dirty cache if available
	db.lock.RLock()
	dirty := db.dirties[hash]
	db.lock.RUnlock()

	if dirty != nil {
		memcacheDirtyHitMeter.Mark(1)
		memcacheDirtyReadMeter.Mark(int64(dirty.size))
		return dirty.obj(hash)
	}
	memcacheDirtyMissMeter.Mark(1)

	// Content unavailable in memory, attempt to retrieve from disk
	enc, err := db.diskdb.Get(hash[:])
	if err != nil || enc == nil {
		return nil
	}
	if db.cleans != nil {
		db.cleans.Set(hash[:], enc)
		memcacheCleanMissMeter.Mark(1)
		memcacheCleanWriteMeter.Mark(int64(len(enc)))
	}
	// The returned value from database is in its own copy,
	// safe to use mustDecodeNodeUnsafe for decoding.
	return mustDecodeNodeUnsafe(hash[:], enc)
}

// Node retrieves an encoded cached trie node from memory. If it cannot be found
// cached, the method queries the persistent database for the content.
func (db *Database) Node(hash common.Hash) ([]byte, error) {
	// It doesn't make sense to retrieve the metaroot
	if hash == (common.Hash{}) {
		return nil, errors.New("not found")
	}
	// Retrieve the node from the clean cache if available
	if db.cleans != nil {
		if enc := db.cleans.Get(nil, hash[:]); enc != nil {
			memcacheCleanHitMeter.Mark(1)
			memcacheCleanReadMeter.Mark(int64(len(enc)))
			return enc, nil
		}
	}
	// Retrieve the node from the dirty cache if available
	db.lock.RLock()
	dirty := db.dirties[hash]
	db.lock.RUnlock()

	if dirty != nil {
		memcacheDirtyHitMeter.Mark(1)
		memcacheDirtyReadMeter.Mark(int64(dirty.size))
		return dirty.rlp(), nil
	}
	memcacheDirtyMissMeter.Mark(1)

	// Content unavailable in memory, attempt to retrieve from disk
	enc := rawdb.ReadTrieNode(db.diskdb, hash)
	if len(enc) != 0 {
		if db.cleans != nil {
			db.cleans.Set(hash[:], enc)
			memcacheCleanMissMeter.Mark(1)
			memcacheCleanWriteMeter.Mark(int64(len(enc)))
		}
		return enc, nil
	}
	return nil, errors.New("not found")
}

// Nodes retrieves the hashes of all the nodes cached within the memory database.
// This method is extremely expensive and should only be used to validate internal
// states in test code.
func (db *Database) Nodes() []common.Hash {
	db.lock.RLock()
	defer db.lock.RUnlock()

	var hashes = make([]common.Hash, 0, len(db.dirties))
	for hash := range db.dirties {
		if hash != (common.Hash{}) { // Special case for "root" references/nodes
			hashes = append(hashes, hash)
		}
	}
	return hashes
}

// Reference adds a new reference from a parent node to a child node.
// This function is used to add reference between internal trie node
// and external node(e.g. storage trie root), all internal trie nodes
// are referenced together by database itself.
func (db *Database) Reference(child common.Hash, parent common.Hash) {
	db.lock.Lock()
	defer db.lock.Unlock()

	db.reference(child, parent)
}

// reference is the private locked version of Reference.
func (db *Database) reference(child common.Hash, parent common.Hash) {
	// If the node does not exist, it's a node pulled from disk, skip
	node, ok := db.dirties[child]
	if !ok {
		return
	}
	// If the reference already exists, only duplicate for roots
	if db.dirties[parent].children == nil {
		db.dirties[parent].children = make(map[common.Hash]uint16)
		db.childrenSize += cachedNodeChildrenSize
	} else if _, ok = db.dirties[parent].children[child]; ok && parent != (common.Hash{}) {
		return
	}
	node.parents++
	db.dirties[parent].children[child]++
	if db.dirties[parent].children[child] == 1 {
		db.childrenSize += common.HashLength + 2 // uint16 counter
	}
}

// Dereference removes an existing reference from a root node.
func (db *Database) Dereference(root common.Hash) {
	// Sanity check to ensure that the meta-root is not removed
	if root == (common.Hash{}) {
		log.Error("Attempted to dereference the trie cache meta root")
		return
	}
	db.lock.Lock()
	defer db.lock.Unlock()

	nodes, storage, start := len(db.dirties), db.dirtiesSize, time.Now()
	db.dereference(root, common.Hash{})

	db.gcnodes += uint64(nodes - len(db.dirties))
	db.gcsize += storage - db.dirtiesSize
	db.gctime += time.Since(start)

	memcacheGCTimeTimer.Update(time.Since(start))
	memcacheGCSizeMeter.Mark(int64(storage - db.dirtiesSize))
	memcacheGCNodesMeter.Mark(int64(nodes - len(db.dirties)))

	log.Debug("Dereferenced trie from memory database", "nodes", nodes-len(db.dirties), "size", storage-db.dirtiesSize, "time", time.Since(start),
		"gcnodes", db.gcnodes, "gcsize", db.gcsize, "gctime", db.gctime, "livenodes", len(db.dirties), "livesize", db.dirtiesSize)
}

// dereference is the private locked version of Dereference.
func (db *Database) dereference(child common.Hash, parent common.Hash) {
	// Dereference the parent-child
	node := db.dirties[parent]

	if node.children != nil && node.children[child] > 0 {
		node.children[child]--
		if node.children[child] == 0 {
			delete(node.children, child)
			db.childrenSize -= (common.HashLength + 2) // uint16 counter
		}
	}
	// If the child does not exist, it's a previously committed node.
	node, ok := db.dirties[child]
	if !ok {
		return
	}
	// If there are no more references to the child, delete it and cascade
	if node.parents > 0 {
		// This is a special cornercase where a node loaded from disk (i.e. not in the
		// memcache any more) gets reinjected as a new node (short node split into full,
		// then reverted into short), causing a cached node to have no parents. That is
		// no problem in itself, but don't make maxint parents out of it.
		node.parents--
	}
	if node.parents == 0 {
		// Remove the node from the flush-list
		switch child {
		case db.oldest:
			db.oldest = node.flushNext
			db.dirties[node.flushNext].flushPrev = common.Hash{}
		case db.newest:
			db.newest = node.flushPrev
			db.dirties[node.flushPrev].flushNext = common.Hash{}
		default:
			db.dirties[node.flushPrev].flushNext = node.flushNext
			db.dirties[node.flushNext].flushPrev = node.flushPrev
		}
		// Dereference all children and delete the node
		node.forChilds(func(hash common.Hash) {
			db.dereference(hash, child)
		})
		delete(db.dirties, child)
		db.dirtiesSize -= common.StorageSize(common.HashLength + int(node.size))
		if node.children != nil {
			db.childrenSize -= cachedNodeChildrenSize
		}
	}
}

// Cap iteratively flushes old but still referenced trie nodes until the total
// memory usage goes below the given threshold.
//
// Note, this method is a non-synchronized mutator. It is unsafe to call this
// concurrently with other mutators.
func (db *Database) Cap(limit common.StorageSize) error {
	// Create a database batch to flush persistent data out. It is important that
	// outside code doesn't see an inconsistent state (referenced data removed from
	// memory cache during commit but not yet in persistent storage). This is ensured
	// by only uncaching existing data when the database write finalizes.
	nodes, storage, start := len(db.dirties), db.dirtiesSize, time.Now()
	batch := db.diskdb.NewBatch()

	// db.dirtiesSize only contains the useful data in the cache, but when reporting
	// the total memory consumption, the maintenance metadata is also needed to be
	// counted.
	size := db.dirtiesSize + common.StorageSize((len(db.dirties)-1)*cachedNodeSize)
	size += db.childrenSize - common.StorageSize(len(db.dirties[common.Hash{}].children)*(common.HashLength+2))

	// If the preimage cache got large enough, push to disk. If it's still small
	// leave for later to deduplicate writes.
	if db.preimages != nil {
		if err := db.preimages.commit(false); err != nil {
			return err
		}
	}
	// Keep committing nodes from the flush-list until we're below allowance
	oldest := db.oldest
	for size > limit && oldest != (common.Hash{}) {
		// Fetch the oldest referenced node and push into the batch
		node := db.dirties[oldest]
		rawdb.WriteTrieNode(batch, oldest, node.rlp())

		// If we exceeded the ideal batch size, commit and reset
		if batch.ValueSize() >= ethdb.IdealBatchSize {
			if err := batch.Write(); err != nil {
				log.Error("Failed to write flush list to disk", "err", err)
				return err
			}
			batch.Reset()
		}
		// Iterate to the next flush item, or abort if the size cap was achieved. Size
		// is the total size, including the useful cached data (hash -> blob), the
		// cache item metadata, as well as external children mappings.
		size -= common.StorageSize(common.HashLength + int(node.size) + cachedNodeSize)
		if node.children != nil {
			size -= common.StorageSize(cachedNodeChildrenSize + len(node.children)*(common.HashLength+2))
		}
		oldest = node.flushNext
	}
	// Flush out any remainder data from the last batch
	if err := batch.Write(); err != nil {
		log.Error("Failed to write flush list to disk", "err", err)
		return err
	}
	// Write successful, clear out the flushed data
	db.lock.Lock()
	defer db.lock.Unlock()

	for db.oldest != oldest {
		node := db.dirties[db.oldest]
		delete(db.dirties, db.oldest)
		db.oldest = node.flushNext

		db.dirtiesSize -= common.StorageSize(common.HashLength + int(node.size))
		if node.children != nil {
			db.childrenSize -= common.StorageSize(cachedNodeChildrenSize + len(node.children)*(common.HashLength+2))
		}
	}
	if db.oldest != (common.Hash{}) {
		db.dirties[db.oldest].flushPrev = common.Hash{}
	}
	db.flushnodes += uint64(nodes - len(db.dirties))
	db.flushsize += storage - db.dirtiesSize
	db.flushtime += time.Since(start)

	memcacheFlushTimeTimer.Update(time.Since(start))
	memcacheFlushSizeMeter.Mark(int64(storage - db.dirtiesSize))
	memcacheFlushNodesMeter.Mark(int64(nodes - len(db.dirties)))

	log.Debug("Persisted nodes from memory database", "nodes", nodes-len(db.dirties), "size", storage-db.dirtiesSize, "time", time.Since(start),
		"flushnodes", db.flushnodes, "flushsize", db.flushsize, "flushtime", db.flushtime, "livenodes", len(db.dirties), "livesize", db.dirtiesSize)

	return nil
}

// Commit iterates over all the children of a particular node, writes them out
// to disk, forcefully tearing down all references in both directions. As a side
// effect, all pre-images accumulated up to this point are also written.
//
// Note, this method is a non-synchronized mutator. It is unsafe to call this
// concurrently with other mutators.
func (db *Database) Commit(node common.Hash, report bool, callback func(common.Hash)) error {
	// Create a database batch to flush persistent data out. It is important that
	// outside code doesn't see an inconsistent state (referenced data removed from
	// memory cache during commit but not yet in persistent storage). This is ensured
	// by only uncaching existing data when the database write finalizes.
	start := time.Now()
	batch := db.diskdb.NewBatch()

	// Move all of the accumulated preimages into a write batch
	if db.preimages != nil {
		if err := db.preimages.commit(true); err != nil {
			return err
		}
	}
	// Move the trie itself into the batch, flushing if enough data is accumulated
	nodes, storage := len(db.dirties), db.dirtiesSize

	uncacher := &cleaner{db}
	if err := db.commit(node, batch, uncacher, callback); err != nil {
		log.Error("Failed to commit trie from trie database", "err", err)
		return err
	}
	// Trie mostly committed to disk, flush any batch leftovers
	if err := batch.Write(); err != nil {
		log.Error("Failed to write trie to disk", "err", err)
		return err
	}
	// Uncache any leftovers in the last batch
	db.lock.Lock()
	defer db.lock.Unlock()
	if err := batch.Replay(uncacher); err != nil {
		return err
	}
	batch.Reset()

	// Reset the storage counters and bumped metrics
	memcacheCommitTimeTimer.Update(time.Since(start))
	memcacheCommitSizeMeter.Mark(int64(storage - db.dirtiesSize))
	memcacheCommitNodesMeter.Mark(int64(nodes - len(db.dirties)))

	logger := log.Info
	if !report {
		logger = log.Debug
	}
	logger("Persisted trie from memory database", "nodes", nodes-len(db.dirties)+int(db.flushnodes), "size", storage-db.dirtiesSize+db.flushsize, "time", time.Since(start)+db.flushtime,
		"gcnodes", db.gcnodes, "gcsize", db.gcsize, "gctime", db.gctime, "livenodes", len(db.dirties), "livesize", db.dirtiesSize)

	// Reset the garbage collection statistics
	db.gcnodes, db.gcsize, db.gctime = 0, 0, 0
	db.flushnodes, db.flushsize, db.flushtime = 0, 0, 0

	return nil
}

// commit is the private locked version of Commit.
func (db *Database) commit(hash common.Hash, batch ethdb.Batch, uncacher *cleaner, callback func(common.Hash)) error {
	// If the node does not exist, it's a previously committed node
	node, ok := db.dirties[hash]
	if !ok {
		return nil
	}
	var err error
	node.forChilds(func(child common.Hash) {
		if err == nil {
			err = db.commit(child, batch, uncacher, callback)
		}
	})
	if err != nil {
		return err
	}
	// If we've reached an optimal batch size, commit and start over
	rawdb.WriteTrieNode(batch, hash, node.rlp())
	if callback != nil {
		callback(hash)
	}
	if batch.ValueSize() >= ethdb.IdealBatchSize {
		if err := batch.Write(); err != nil {
			return err
		}
		db.lock.Lock()
		err := batch.Replay(uncacher)
		batch.Reset()
		db.lock.Unlock()
		if err != nil {
			return err
		}
	}
	return nil
}

// cleaner is a database batch replayer that takes a batch of write operations
// and cleans up the trie database from anything written to disk.
type cleaner struct {
	db *Database
}

// Put reacts to database writes and implements dirty data uncaching. This is the
// post-processing step of a commit operation where the already persisted trie is
// removed from the dirty cache and moved into the clean cache. The reason behind
// the two-phase commit is to ensure data availability while moving from memory
// to disk.
func (c *cleaner) Put(key []byte, rlp []byte) error {
	hash := common.BytesToHash(key)

	// If the node does not exist, we're done on this path
	node, ok := c.db.dirties[hash]
	if !ok {
		return nil
	}
	// Node still exists, remove it from the flush-list
	switch hash {
	case c.db.oldest:
		c.db.oldest = node.flushNext
		c.db.dirties[node.flushNext].flushPrev = common.Hash{}
	case c.db.newest:
		c.db.newest = node.flushPrev
		c.db.dirties[node.flushPrev].flushNext = common.Hash{}
	default:
		c.db.dirties[node.flushPrev].flushNext = node.flushNext
		c.db.dirties[node.flushNext].flushPrev = node.flushPrev
	}
	// Remove the node from the dirty cache
	delete(c.db.dirties, hash)
	c.db.dirtiesSize -= common.StorageSize(common.HashLength + int(node.size))
	if node.children != nil {
		c.db.childrenSize -= common.StorageSize(cachedNodeChildrenSize + len(node.children)*(common.HashLength+2))
	}
	// Move the flushed node into the clean cache to prevent insta-reloads
	if c.db.cleans != nil {
		c.db.cleans.Set(hash[:], rlp)
		memcacheCleanWriteMeter.Mark(int64(len(rlp)))
	}
	return nil
}

func (c *cleaner) Delete(key []byte) error {
	panic("not implemented")
}

// Update inserts the dirty nodes in provided nodeset into database and
// link the account trie with multiple storage tries if necessary.
func (db *Database) Update(nodes *MergedNodeSet) error {
	db.lock.Lock()
	defer db.lock.Unlock()

	// Insert dirty nodes into the database. In the same tree, it must be
	// ensured that children are inserted first, then parent so that children
	// can be linked with their parent correctly.
	//
	// Note, the storage tries must be flushed before the account trie to
	// retain the invariant that children go into the dirty cache first.
	var order []common.Hash
	for owner := range nodes.sets {
		if owner == (common.Hash{}) {
			continue
		}
		order = append(order, owner)
	}
	if _, ok := nodes.sets[common.Hash{}]; ok {
		order = append(order, common.Hash{})
	}
	for _, owner := range order {
		subset := nodes.sets[owner]
		for _, path := range subset.updates.order {
			n, ok := subset.updates.nodes[path]
			if !ok {
				return fmt.Errorf("missing node %x %v", owner, path)
			}
			db.insert(n.hash, int(n.size), n.node)
		}
	}
	// Link up the account trie and storage trie if the node points
	// to an account trie leaf.
	if set, present := nodes.sets[common.Hash{}]; present {
		for _, n := range set.leaves {
			var account types.StateAccount
			if err := rlp.DecodeBytes(n.blob, &account); err != nil {
				return err
			}
			if account.Root != emptyRoot {
				db.reference(account.Root, n.parent)
			}
		}
	}
	return nil
}

// Size returns the current storage size of the memory cache in front of the
// persistent database layer.
func (db *Database) Size() (common.StorageSize, common.StorageSize) {
	db.lock.RLock()
	defer db.lock.RUnlock()

	// db.dirtiesSize only contains the useful data in the cache, but when reporting
	// the total memory consumption, the maintenance metadata is also needed to be
	// counted.
	var metadataSize = common.StorageSize((len(db.dirties) - 1) * cachedNodeSize)
	var metarootRefs = common.StorageSize(len(db.dirties[common.Hash{}].children) * (common.HashLength + 2))
	var preimageSize common.StorageSize
	if db.preimages != nil {
		preimageSize = db.preimages.size()
	}
	return db.dirtiesSize + db.childrenSize + metadataSize - metarootRefs, preimageSize
}

// GetReader retrieves a node reader belonging to the given state root.
func (db *Database) GetReader(root common.Hash) Reader {
	return newHashReader(db)
}

// hashReader is reader of hashDatabase which implements the Reader interface.
type hashReader struct {
	db *Database
}

// newHashReader initializes the hash reader.
func newHashReader(db *Database) *hashReader {
	return &hashReader{db: db}
}

// Node retrieves the trie node with the given node hash.
// No error will be returned if the node is not found.
func (reader *hashReader) Node(_ common.Hash, _ []byte, hash common.Hash) (node, error) {
	return reader.db.node(hash), nil
}

// NodeBlob retrieves the RLP-encoded trie node blob with the given node hash.
// No error will be returned if the node is not found.
func (reader *hashReader) NodeBlob(_ common.Hash, _ []byte, hash common.Hash) ([]byte, error) {
	blob, _ := reader.db.Node(hash)
	return blob, nil
}

// saveCache saves clean state cache to given directory path
// using specified CPU cores.
func (db *Database) saveCache(dir string, threads int) error {
	if db.cleans == nil {
		return nil
	}
	log.Info("Writing clean trie cache to disk", "path", dir, "threads", threads)

	start := time.Now()
	err := db.cleans.SaveToFileConcurrent(dir, threads)
	if err != nil {
		log.Error("Failed to persist clean trie cache", "error", err)
		return err
	}
	log.Info("Persisted the clean trie cache", "path", dir, "elapsed", common.PrettyDuration(time.Since(start)))
	return nil
}

// SaveCache atomically saves fast cache data to the given dir using all
// available CPU cores.
func (db *Database) SaveCache(dir string) error {
	return db.saveCache(dir, runtime.GOMAXPROCS(0))
}

// SaveCachePeriodically atomically saves fast cache data to the given dir with
// the specified interval. All dump operation will only use a single CPU core.
func (db *Database) SaveCachePeriodically(dir string, interval time.Duration, stopCh <-chan struct{}) {
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			db.saveCache(dir, 1)
		case <-stopCh:
			return
		}
	}
}

// CommitPreimages flushes the dangling preimages to disk. It is meant to be
// called when closing the blockchain object, so that preimages are persisted
// to the database.
func (db *Database) CommitPreimages() error {
	db.lock.Lock()
	defer db.lock.Unlock()

	if db.preimages == nil {
		return nil
	}
	return db.preimages.commit(true)
}