Faster synchronization with asynchronous deletion of old checkpoints

.github/workflows/release.yml

@@ -1,30 +0,0 @@
-name: goreleaser
-
-on:
-  push:
-    tags:
-      - '*'
-
-jobs:
-  goreleaser:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v2
-        with:
-          fetch-depth: 0
-      - name: Set up Go
-        uses: actions/setup-go@v2
-        with:
-          go-version: 1.16
-      - name: Get packr
-        run: go get -u github.com/gobuffalo/packr
-      - name: Prepare
-        run: git reset --hard
-      - name: Run GoReleaser
-        uses: goreleaser/goreleaser-action@v2
-        with:
-          version: latest
-          args: release --rm-dist
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.goreleaser.yml

@@ -1,26 +0,0 @@
-before:
-  hooks:
-    - go mod download
-
-builds:
-  - main: ./cli/node/main.go
-    binary: node
-    id: node
-    goos:
-      - linux
-      - darwin
-    goarch:
-      - amd64
-
-checksum:
-  name_template: 'checksums.txt'
-
-snapshot:
-  name_template: "{{ .Tag }}-next"
-
-changelog:
-  sort: asc
-  filters:
-    exclude:
-      - '^docs:'
-      - '^test:'

Makefile

@@ -3,8 +3,8 @@
 # Project variables.
 PACKAGE := github.com/hermeznetwork/hermez-node
 VERSION := $(shell git describe --tags --always)
-COMMIT := $(shell git rev-parse --short HEAD)
-DATE := $(shell date +%Y-%m-%dT%H:%M:%S%z)
+BUILD := $(shell git rev-parse --short HEAD)
+BUILD_DATE := $(shell date +%Y-%m-%dT%H:%M:%S%z)
 PROJECT_NAME := $(shell basename "$(PWD)")
 
 # Go related variables.
@@ -23,7 +23,7 @@ CONFIG ?= $(GOBASE)/cli/node/cfg.buidler.toml
 POSTGRES_PASS ?= yourpasswordhere
 
 # Use linker flags to provide version/build settings.
-LDFLAGS=-ldflags "-X main.version=$(VERSION) -X main.commit=$(COMMIT) -X main.date=$(DATE)"
+LDFLAGS=-ldflags "-X=main.Version=$(VERSION) -X=main.Build=$(BUILD) -X=main.Date=$(BUILD_DATE)"
 
 # PID file will keep the process id of the server.
 PID_PROOF_MOCK := /tmp/.$(PROJECT_NAME).proof.pid
@@ -94,11 +94,11 @@ install:
 	@echo "  >  Checking if there is any missing dependencies..."
 	$(GOENVVARS) go get $(GOCMD)/... $(get)
 
-## run-node: Run Hermez node.
-run-node:
+## run: Run Hermez node.
+run:
 	@bash -c "$(MAKE) clean build"
 	@echo "  >  Running $(PROJECT_NAME)"
-	@$(GOBIN)/$(GOBINARY) run --mode $(MODE) --cfg $(CONFIG)
+	@$(GOBIN)/$(GOBINARY) --mode $(MODE) --cfg $(CONFIG) run
 
 ## run-proof-mock: Run proof server mock API.
 run-proof-mock: stop-proof-mock

README.md

@@ -25,13 +25,13 @@ there are more information about the config file into [cli/node/README.md](cli/n
 After setting the config, you can build and run the Hermez Node as a synchronizer:
 
 ```shell
-$ make run-node
+$ make run
 ```
 
 Or build and run as a coordinator, and also passing the config file from other location:
 
 ```shell
-$ MODE=sync CONFIG=cli/node/cfg.buidler.toml make run-node
+$ MODE=sync CONFIG=cli/node/cfg.buidler.toml make run
 ```
 
 To check the useful make commands:

api/api_test.go

@@ -522,16 +522,11 @@ func TestMain(m *testing.M) {
 		WithdrawalDelay: uint64(3000),
 	}
 
-	stateAPIUpdater, err = stateapiupdater.NewUpdater(hdb, nodeConfig, &common.SCVariables{
+	stateAPIUpdater = stateapiupdater.NewUpdater(hdb, nodeConfig, &common.SCVariables{
 		Rollup:   rollupVars,
 		Auction:  auctionVars,
 		WDelayer: wdelayerVars,
-	}, constants, &stateapiupdater.RecommendedFeePolicy{
-		PolicyType: stateapiupdater.RecommendedFeePolicyTypeAvgLastHour,
-	})
-	if err != nil {
-		panic(err)
-	}
+	}, constants)
 
 	// Generate test data, as expected to be received/sended from/to the API
 	testCoords := genTestCoordinators(commonCoords)

api/stateapiupdater/stateapiupdater.go

@@ -2,12 +2,10 @@ package stateapiupdater
 
 import (
 	"database/sql"
-	"fmt"
 	"sync"
 
 	"github.com/hermeznetwork/hermez-node/common"
 	"github.com/hermeznetwork/hermez-node/db/historydb"
-	"github.com/hermeznetwork/hermez-node/log"
 	"github.com/hermeznetwork/tracerr"
 )
 
@@ -19,45 +17,11 @@ type Updater struct {
 	vars   common.SCVariablesPtr
 	consts historydb.Constants
 	rw     sync.RWMutex
-	rfp    *RecommendedFeePolicy
-}
-
-// RecommendedFeePolicy describes how the recommended fee is calculated
-type RecommendedFeePolicy struct {
-	PolicyType  RecommendedFeePolicyType `validate:"required"`
-	StaticValue float64
-}
-
-// RecommendedFeePolicyType describes the different available recommended fee strategies
-type RecommendedFeePolicyType string
-
-const (
-	// RecommendedFeePolicyTypeStatic always give the same StaticValue as recommended fee
-	RecommendedFeePolicyTypeStatic RecommendedFeePolicyType = "Static"
-	// RecommendedFeePolicyTypeAvgLastHour set the recommended fee using the average fee of the last hour
-	RecommendedFeePolicyTypeAvgLastHour RecommendedFeePolicyType = "AvgLastHour"
-)
-
-func (rfp *RecommendedFeePolicy) valid() bool {
-	switch rfp.PolicyType {
-	case RecommendedFeePolicyTypeStatic:
-		if rfp.StaticValue == 0 {
-			log.Warn("RcommendedFee is set to 0 USD, and the policy is static")
-		}
-		return true
-	case RecommendedFeePolicyTypeAvgLastHour:
-		return true
-	default:
-		return false
-	}
 }
 
 // NewUpdater creates a new Updater
 func NewUpdater(hdb *historydb.HistoryDB, config *historydb.NodeConfig, vars *common.SCVariables,
-	consts *historydb.Constants, rfp *RecommendedFeePolicy) (*Updater, error) {
-	if ok := rfp.valid(); !ok {
-		return nil, tracerr.Wrap(fmt.Errorf("Invalid recommended fee policy: %v", rfp.PolicyType))
-	}
+	consts *historydb.Constants) *Updater {
 	u := Updater{
 		hdb:    hdb,
 		config: *config,
@@ -67,10 +31,9 @@ func NewUpdater(hdb *historydb.HistoryDB, config *historydb.NodeConfig, vars *co
 				ForgeDelay: config.ForgeDelay,
 			},
 		},
-		rfp: rfp,
 	}
 	u.SetSCVars(vars.AsPtr())
-	return &u, nil
+	return &u
 }
 
 // Store the State in the HistoryDB
@@ -102,16 +65,6 @@ func (u *Updater) SetSCVars(vars *common.SCVariablesPtr) {
 
 // UpdateRecommendedFee update Status.RecommendedFee information
 func (u *Updater) UpdateRecommendedFee() error {
-	switch u.rfp.PolicyType {
-	case RecommendedFeePolicyTypeStatic:
-		u.rw.Lock()
-		u.state.RecommendedFee = common.RecommendedFee{
-			ExistingAccount:        u.rfp.StaticValue,
-			CreatesAccount:         u.rfp.StaticValue,
-			CreatesAccountInternal: u.rfp.StaticValue,
-		}
-		u.rw.Unlock()
-	case RecommendedFeePolicyTypeAvgLastHour:
 	recommendedFee, err := u.hdb.GetRecommendedFee(u.config.MinFeeUSD, u.config.MaxFeeUSD)
 	if err != nil {
 		return tracerr.Wrap(err)
@@ -119,10 +72,6 @@ func (u *Updater) UpdateRecommendedFee() error {
 	u.rw.Lock()
 	u.state.RecommendedFee = *recommendedFee
 	u.rw.Unlock()
-	default:
-		return tracerr.New("Invalid recommende fee policy")
-	}
-
 	return nil
 }
 

cli/node/README.md

@@ -73,9 +73,6 @@ of the node configuration.  Please, check the `type APIServer` at
   monitor the size of the folder to avoid running out of space.
 - The node requires a PostgreSQL database.  The parameters of the server and
   database must be set in the `PostgreSQL` section.
-- The node requires a web3 RPC server to work.  The node has only been tested
-  with geth and may not work correctly with other ethereum nodes
-  implementations.
 
 ## Building
 

cli/node/cfg.buidler.toml

@@ -145,11 +145,3 @@ Coordinator = true
 BatchPath = "/tmp/iden3-test/hermez/batchesdebug"
 LightScrypt = true
 # RollupVerifierIndex = 0
-
-[RecommendedFeePolicy]
-# Strategy used to calculate the recommended fee that the API will expose.
-# Available options:
-# - Static: always return the same value (StaticValue) in USD
-# - AvgLastHour: calculate using the average fee of the forged transactions during the last hour
-PolicyType = "Static"
-StaticValue = 0.99

cli/node/main.go

@@ -35,18 +35,18 @@ const (
 )
 
 var (
-	// version represents the program based on the git tag
-	version = "v0.1.0"
-	// commit represents the program based on the git commit
-	commit = "dev"
-	// date represents the date of application was built
-	date = ""
+	// Version represents the program based on the git tag
+	Version = "v0.1.0"
+	// Build represents the program based on the git commit
+	Build = "dev"
+	// Date represents the date of application was built
+	Date = ""
 )
 
 func cmdVersion(c *cli.Context) error {
-	fmt.Printf("Version = \"%v\"\n", version)
-	fmt.Printf("Build = \"%v\"\n", commit)
-	fmt.Printf("Date = \"%v\"\n", date)
+	fmt.Printf("Version = \"%v\"\n", Version)
+	fmt.Printf("Build = \"%v\"\n", Build)
+	fmt.Printf("Date = \"%v\"\n", Date)
 	return nil
 }
 
@@ -421,7 +421,7 @@ func getConfigAPIServer(c *cli.Context) (*ConfigAPIServer, error) {
 func main() {
 	app := cli.NewApp()
 	app.Name = "hermez-node"
-	app.Version = version
+	app.Version = Version
 	flags := []cli.Flag{
 		&cli.StringFlag{
 			Name:     flagMode,

config/config.go

@@ -8,7 +8,6 @@ import (
 
 	"github.com/BurntSushi/toml"
 	ethCommon "github.com/ethereum/go-ethereum/common"
-	"github.com/hermeznetwork/hermez-node/api/stateapiupdater"
 	"github.com/hermeznetwork/hermez-node/common"
 	"github.com/hermeznetwork/hermez-node/priceupdater"
 	"github.com/hermeznetwork/tracerr"
@@ -300,8 +299,7 @@ type Node struct {
 	} `validate:"required"`
 	PostgreSQL PostgreSQL `validate:"required"`
 	Web3       struct {
-		// URL is the URL of the web3 ethereum-node RPC server.  Only
-		// geth is officially supported.
+		// URL is the URL of the web3 ethereum-node RPC server
 		URL string `validate:"required"`
 	} `validate:"required"`
 	Synchronizer struct {
@@ -348,7 +346,6 @@ type Node struct {
 		// can wait to stablish a SQL connection
 		SQLConnectionTimeout Duration
 	} `validate:"required"`
-	RecommendedFeePolicy stateapiupdater.RecommendedFeePolicy `validate:"required"`
 	Debug       NodeDebug   `validate:"required"`
 	Coordinator Coordinator `validate:"-"`
 }

coordinator/coordinator.go

@@ -1,43 +1,3 @@
-/*
-Package coordinator handles all the logic related to forging batches as a
-coordinator in the hermez network.
-
-The forging of batches is done with a pipeline in order to allow multiple
-batches being forged in parallel.  The maximum number of batches that can be
-forged in parallel is determined by the number of available proof servers.
-
-The Coordinator begins with the pipeline stopped.  The main Coordinator
-goroutine keeps listening for synchronizer events sent by the node package,
-which allow the coordinator to determine if the configured forger address is
-allowed to forge at the current block or not.  When the forger address becomes
-allowed to forge, the pipeline is started, and when it terminates being allowed
-to forge, the pipeline is stopped.
-
-The Pipeline consists of two goroutines.  The first one is in charge of
-preparing a batch internally, which involves making a selection of transactions
-and calculating the ZKInputs for the batch proof, and sending these ZKInputs to
-an idle proof server.  This goroutine will keep preparing batches while there
-are idle proof servers, if the forging policy determines that a batch should be
-forged in the current state.  The second goroutine is in charge of waiting for
-the proof server to finish computing the proof, retreiving it, prepare the
-arguments for the `forgeBatch` Rollup transaction, and sending the result to
-the TxManager.  All the batch information moves between functions and
-goroutines via the BatchInfo struct.
-
-Finally, the TxManager contains a single goroutine that makes forgeBatch
-ethereum transactions for the batches sent by the Pipeline, and keeps them in a
-list to check them periodically.  In the periodic checks, the ethereum
-transaction is checked for successfulness, and it's only forgotten after a
-number of confirmation blocks have passed after being successfully mined.  At
-any point if a transaction failure is detected, the TxManager can signal the
-Coordinator to reset the Pipeline in order to reforge the failed batches.
-
-The Coordinator goroutine acts as a manager.  The synchronizer events (which
-notify about new blocks and associated new state) that it receives are
-broadcasted to the Pipeline and the TxManager.  This allows the Coordinator,
-Pipeline and TxManager to have a copy of the current hermez network state
-required to perform their duties.
-*/
 package coordinator
 
 import (

db/kvdb/kvdb.go

@@ -49,6 +49,8 @@ type KVDB struct {
 	CurrentIdx   common.Idx
 	CurrentBatch common.BatchNum
 	m            sync.Mutex
+	mutexDelOld  sync.Mutex
+	wg           sync.WaitGroup
 	last         *Last
 }
 
@@ -444,10 +446,15 @@ func (k *KVDB) MakeCheckpoint() error {
 			return tracerr.Wrap(err)
 		}
 	}
-	// delete old checkpoints
-	if err := k.deleteOldCheckpoints(); err != nil {
-		return tracerr.Wrap(err)
+
+	k.wg.Add(1)
+	go func() {
+		delErr := k.DeleteOldCheckpoints()
+		if delErr != nil {
+			log.Errorw("delete old checkpoints failed", "err", delErr)
 		}
+		k.wg.Done()
+	}()
 
 	return nil
 }
@@ -509,9 +516,12 @@ func (k *KVDB) ListCheckpoints() ([]int, error) {
 	return checkpoints, nil
 }
 
-// deleteOldCheckpoints deletes old checkpoints when there are more than
+// DeleteOldCheckpoints deletes old checkpoints when there are more than
 // `s.keep` checkpoints
-func (k *KVDB) deleteOldCheckpoints() error {
+func (k *KVDB) DeleteOldCheckpoints() error {
+	k.mutexDelOld.Lock()
+	defer k.mutexDelOld.Unlock()
+
 	list, err := k.ListCheckpoints()
 	if err != nil {
 		return tracerr.Wrap(err)
@@ -584,4 +594,6 @@ func (k *KVDB) Close() {
 	if k.last != nil {
 		k.last.close()
 	}
+	// wait for deletion of old checkpoints
+	k.wg.Wait()
 }

db/kvdb/kvdb_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
+	"sync"
 	"testing"
 
 	"github.com/hermeznetwork/hermez-node/common"
@@ -190,12 +191,67 @@ func TestDeleteOldCheckpoints(t *testing.T) {
 	for i := 0; i < numCheckpoints; i++ {
 		err = db.MakeCheckpoint()
 		require.NoError(t, err)
+		err = db.DeleteOldCheckpoints()
+		require.NoError(t, err)
 		checkpoints, err := db.ListCheckpoints()
 		require.NoError(t, err)
 		assert.LessOrEqual(t, len(checkpoints), keep)
 	}
 }
 
+func TestConcurrentDeleteOldCheckpoints(t *testing.T) {
+	dir, err := ioutil.TempDir("", "tmpdb")
+	require.NoError(t, err)
+	defer require.NoError(t, os.RemoveAll(dir))
+
+	keep := 16
+	db, err := NewKVDB(Config{Path: dir, Keep: keep})
+	require.NoError(t, err)
+
+	numCheckpoints := 32
+
+	var wg sync.WaitGroup
+	wg.Add(numCheckpoints)
+
+	// do checkpoints and check that we never have more than `keep`
+	// checkpoints.
+	// 1 async DeleteOldCheckpoint after 1 MakeCheckpoint
+	for i := 0; i < numCheckpoints; i++ {
+		err = db.MakeCheckpoint()
+		require.NoError(t, err)
+		go func() {
+			err = db.DeleteOldCheckpoints()
+			require.NoError(t, err)
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+	checkpoints, err := db.ListCheckpoints()
+	require.NoError(t, err)
+	assert.LessOrEqual(t, len(checkpoints), keep)
+
+	wg.Add(numCheckpoints)
+
+	// do checkpoints and check that we never have more than `keep`
+	// checkpoints
+	// 32 concurrent DeleteOldCheckpoint after 32 MakeCheckpoint
+	for i := 0; i < numCheckpoints; i++ {
+		err = db.MakeCheckpoint()
+		require.NoError(t, err)
+	}
+	for i := 0; i < numCheckpoints; i++ {
+		go func() {
+			err = db.DeleteOldCheckpoints()
+			require.NoError(t, err)
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+	checkpoints, err = db.ListCheckpoints()
+	require.NoError(t, err)
+	assert.LessOrEqual(t, len(checkpoints), keep)
+}
+
 func TestGetCurrentIdx(t *testing.T) {
 	dir, err := ioutil.TempDir("", "tmpdb")
 	require.NoError(t, err)

db/statedb/statedb.go

@@ -227,6 +227,12 @@ func (s *StateDB) MakeCheckpoint() error {
 	return s.db.MakeCheckpoint()
 }
 
+// DeleteOldCheckpoints deletes old checkpoints when there are more than
+// `cfg.keep` checkpoints
+func (s *StateDB) DeleteOldCheckpoints() error {
+	return s.db.DeleteOldCheckpoints()
+}
+
 // CurrentBatch returns the current in-memory CurrentBatch of the StateDB.db
 func (s *StateDB) CurrentBatch() common.BatchNum {
 	return s.db.CurrentBatch

db/statedb/statedb_test.go

@@ -7,6 +7,7 @@ import (
 	"math/big"
 	"os"
 	"strings"
+	"sync"
 	"testing"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
@@ -588,6 +589,48 @@ func TestDeleteOldCheckpoints(t *testing.T) {
 	for i := 0; i < numCheckpoints; i++ {
 		err = sdb.MakeCheckpoint()
 		require.NoError(t, err)
+		err := sdb.DeleteOldCheckpoints()
+		require.NoError(t, err)
+		checkpoints, err := sdb.db.ListCheckpoints()
+		require.NoError(t, err)
+		assert.LessOrEqual(t, len(checkpoints), keep)
+	}
+}
+
+// TestConcurrentDeleteOldCheckpoints performs almost the same test than
+// kvdb/kvdb_test.go TestConcurrentDeleteOldCheckpoints, but over the StateDB
+func TestConcurrentDeleteOldCheckpoints(t *testing.T) {
+	dir, err := ioutil.TempDir("", "tmpdb")
+	require.NoError(t, err)
+	defer require.NoError(t, os.RemoveAll(dir))
+
+	keep := 16
+	sdb, err := NewStateDB(Config{Path: dir, Keep: keep, Type: TypeSynchronizer, NLevels: 32})
+	require.NoError(t, err)
+
+	numCheckpoints := 32
+	// do checkpoints and check that we never have more than `keep`
+	// checkpoints
+	for i := 0; i < numCheckpoints; i++ {
+		err = sdb.MakeCheckpoint()
+		require.NoError(t, err)
+		wg := sync.WaitGroup{}
+		n := 10
+		wg.Add(n)
+		for j := 0; j < n; j++ {
+			go func() {
+				err := sdb.DeleteOldCheckpoints()
+				require.NoError(t, err)
+				checkpoints, err := sdb.db.ListCheckpoints()
+				require.NoError(t, err)
+				assert.LessOrEqual(t, len(checkpoints), keep)
+				wg.Done()
+			}()
+			_, err := sdb.db.ListCheckpoints()
+			// only checking here for absence of errors, not the count of checkpoints
+			require.NoError(t, err)
+		}
+		wg.Wait()
 		checkpoints, err := sdb.db.ListCheckpoints()
 		require.NoError(t, err)
 		assert.LessOrEqual(t, len(checkpoints), keep)

eth/ethereum.go

@@ -245,15 +245,15 @@ func (c *EthereumClient) EthBlockByNumber(ctx context.Context, number int64) (*c
 	if number == -1 {
 		blockNum = nil
 	}
-	block, err := c.client.BlockByNumber(ctx, blockNum)
+	header, err := c.client.HeaderByNumber(ctx, blockNum)
 	if err != nil {
 		return nil, tracerr.Wrap(err)
 	}
 	b := &common.Block{
-		Num:        block.Number().Int64(),
-		Timestamp:  time.Unix(int64(block.Time()), 0),
-		ParentHash: block.ParentHash(),
-		Hash:       block.Hash(),
+		Num:        header.Number.Int64(),
+		Timestamp:  time.Unix(int64(header.Time), 0),
+		ParentHash: header.ParentHash,
+		Hash:       header.Hash(),
 	}
 	return b, nil
 }

node/node.go

@@ -1,18 +1,3 @@
-/*
-Package node does the initialization of all the required objects to either run
-as a synchronizer or as a coordinator.
-
-The Node contains several goroutines that run in the background or that
-periodically perform tasks.  One of this goroutines periodically calls the
-`Synchronizer.Sync` function, allowing the synchronization of one block at a
-time.  After every call to `Synchronizer.Sync`, the Node sends a message to the
-Coordinator to notify it about the new synced block (and associated state) or
-reorg (and resetted state) in case one happens.
-
-Other goroutines perform tasks such as: updating the token prices, update
-metrics stored in the historyDB, update recommended fee stored in the
-historyDB, run the http API server, run the debug http API server, etc.
-*/
 package node
 
 import (
@@ -288,16 +273,7 @@ func NewNode(mode Mode, cfg *config.Node) (*Node, error) {
 		return nil, tracerr.Wrap(err)
 	}
 
-	stateAPIUpdater, err := stateapiupdater.NewUpdater(
-		historyDB,
-		&hdbNodeCfg,
-		initSCVars,
-		&hdbConsts,
-		&cfg.RecommendedFeePolicy,
-	)
-	if err != nil {
-		return nil, tracerr.Wrap(err)
-	}
+	stateAPIUpdater := stateapiupdater.NewUpdater(historyDB, &hdbNodeCfg, initSCVars, &hdbConsts)
 
 	var coord *coordinator.Coordinator
 	if mode == ModeCoordinator {

synchronizer/synchronizer.go

@@ -1,35 +1,3 @@
-/*
-Package synchronizer synchronizes the hermez network state by querying events
-emitted by the three smart contracts: `Hermez.sol` (referred as Rollup here),
-`HermezAuctionProtocol.sol` (referred as Auction here) and
-`WithdrawalDelayer.sol` (referred as WDelayer here).
-
-The main entry point for synchronization is the `Sync` function, which at most
-will synchronize one ethereum block, and all the hermez events that happened in
-that block.  During a `Sync` call, a reorg can be detected; in such case, uncle
-blocks will be discarded, and only in a future `Sync` call correct blocks will
-be synced.
-
-The synchronization of the events in each smart contracts are done
-in the methods `rollupSync`, `auctionSync` and `wdelayerSync`, which in turn
-use the interface code to read each smart contract state and events found in
-"github.com/hermeznetwork/hermez-node/eth".  After these three methods are
-called, an object of type `common.BlockData` is built containing all the
-updates and events that happened in that block, and it is inserted in the
-HistoryDB in a single SQL transaction.
-
-`rollupSync` is the method that synchronizes batches sent via the `forgeBatch`
-transaction in `Hermez.sol`.  In `rollupSync`, for every batch,  the accounts
-state is updated in the StateDB by processing all transactions that have been
-forged in that batch.
-
-The consistency of the stored data is guaranteed by the HistoryDB: All the
-block information is inserted in a single SQL transaction at the end of the
-`Sync` method, once the StateDB has been updated.  And every time the
-Synchronizer starts, it continues from the last block in the HistoryDB.  The
-StateDB stores updates organized by checkpoints for every batch, and each batch
-is only accessed if it appears in the HistoryDB.
-*/
 package synchronizer
 
 import (