Official Go implementation of the Ethereum protocol
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go-ethereum/core/state/trie_prefetcher.go

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// Copyright 2020 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 state
import (
"errors"
"sync"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/log"
"github.com/ethereum/go-ethereum/metrics"
)
var (
// triePrefetchMetricsPrefix is the prefix under which to publish the metrics.
triePrefetchMetricsPrefix = "trie/prefetch/"
// errTerminated is returned if a fetcher is attempted to be operated after it
// has already terminated.
errTerminated = errors.New("fetcher is already terminated")
)
// triePrefetcher is an active prefetcher, which receives accounts or storage
// items and does trie-loading of them. The goal is to get as much useful content
// into the caches as possible.
//
// Note, the prefetcher's API is not thread safe.
type triePrefetcher struct {
db Database // Database to fetch trie nodes through
root common.Hash // Root hash of the account trie for metrics
fetchers map[string]*subfetcher // Subfetchers for each trie
term chan struct{} // Channel to signal interruption
noreads bool // Whether to ignore state-read-only prefetch requests
deliveryMissMeter metrics.Meter
accountLoadReadMeter metrics.Meter
accountLoadWriteMeter metrics.Meter
accountDupReadMeter metrics.Meter
accountDupWriteMeter metrics.Meter
accountDupCrossMeter metrics.Meter
accountWasteMeter metrics.Meter
storageLoadReadMeter metrics.Meter
storageLoadWriteMeter metrics.Meter
storageDupReadMeter metrics.Meter
storageDupWriteMeter metrics.Meter
storageDupCrossMeter metrics.Meter
storageWasteMeter metrics.Meter
}
func newTriePrefetcher(db Database, root common.Hash, namespace string, noreads bool) *triePrefetcher {
prefix := triePrefetchMetricsPrefix + namespace
return &triePrefetcher{
db: db,
root: root,
fetchers: make(map[string]*subfetcher), // Active prefetchers use the fetchers map
term: make(chan struct{}),
noreads: noreads,
deliveryMissMeter: metrics.GetOrRegisterMeter(prefix+"/deliverymiss", nil),
accountLoadReadMeter: metrics.GetOrRegisterMeter(prefix+"/account/load/read", nil),
accountLoadWriteMeter: metrics.GetOrRegisterMeter(prefix+"/account/load/write", nil),
accountDupReadMeter: metrics.GetOrRegisterMeter(prefix+"/account/dup/read", nil),
accountDupWriteMeter: metrics.GetOrRegisterMeter(prefix+"/account/dup/write", nil),
accountDupCrossMeter: metrics.GetOrRegisterMeter(prefix+"/account/dup/cross", nil),
accountWasteMeter: metrics.GetOrRegisterMeter(prefix+"/account/waste", nil),
storageLoadReadMeter: metrics.GetOrRegisterMeter(prefix+"/storage/load/read", nil),
storageLoadWriteMeter: metrics.GetOrRegisterMeter(prefix+"/storage/load/write", nil),
storageDupReadMeter: metrics.GetOrRegisterMeter(prefix+"/storage/dup/read", nil),
storageDupWriteMeter: metrics.GetOrRegisterMeter(prefix+"/storage/dup/write", nil),
storageDupCrossMeter: metrics.GetOrRegisterMeter(prefix+"/storage/dup/cross", nil),
storageWasteMeter: metrics.GetOrRegisterMeter(prefix+"/storage/waste", nil),
}
}
// terminate iterates over all the subfetchers and issues a termination request
// to all of them. Depending on the async parameter, the method will either block
// until all subfetchers spin down, or return immediately.
func (p *triePrefetcher) terminate(async bool) {
// Short circuit if the fetcher is already closed
select {
case <-p.term:
return
default:
}
// Terminate all sub-fetchers, sync or async, depending on the request
for _, fetcher := range p.fetchers {
fetcher.terminate(async)
}
close(p.term)
}
// report aggregates the pre-fetching and usage metrics and reports them.
func (p *triePrefetcher) report() {
if !metrics.Enabled {
return
}
for _, fetcher := range p.fetchers {
fetcher.wait() // ensure the fetcher's idle before poking in its internals
if fetcher.root == p.root {
p.accountLoadReadMeter.Mark(int64(len(fetcher.seenRead)))
p.accountLoadWriteMeter.Mark(int64(len(fetcher.seenWrite)))
p.accountDupReadMeter.Mark(int64(fetcher.dupsRead))
p.accountDupWriteMeter.Mark(int64(fetcher.dupsWrite))
p.accountDupCrossMeter.Mark(int64(fetcher.dupsCross))
for _, key := range fetcher.used {
delete(fetcher.seenRead, string(key))
delete(fetcher.seenWrite, string(key))
}
p.accountWasteMeter.Mark(int64(len(fetcher.seenRead) + len(fetcher.seenWrite)))
} else {
p.storageLoadReadMeter.Mark(int64(len(fetcher.seenRead)))
p.storageLoadWriteMeter.Mark(int64(len(fetcher.seenWrite)))
p.storageDupReadMeter.Mark(int64(fetcher.dupsRead))
p.storageDupWriteMeter.Mark(int64(fetcher.dupsWrite))
p.storageDupCrossMeter.Mark(int64(fetcher.dupsCross))
for _, key := range fetcher.used {
delete(fetcher.seenRead, string(key))
delete(fetcher.seenWrite, string(key))
}
p.storageWasteMeter.Mark(int64(len(fetcher.seenRead) + len(fetcher.seenWrite)))
}
}
}
// prefetch schedules a batch of trie items to prefetch. After the prefetcher is
// closed, all the following tasks scheduled will not be executed and an error
// will be returned.
//
// prefetch is called from two locations:
//
// 1. Finalize of the state-objects storage roots. This happens at the end
// of every transaction, meaning that if several transactions touches
// upon the same contract, the parameters invoking this method may be
// repeated.
// 2. Finalize of the main account trie. This happens only once per block.
func (p *triePrefetcher) prefetch(owner common.Hash, root common.Hash, addr common.Address, keys [][]byte, read bool) error {
// If the state item is only being read, but reads are disabled, return
if read && p.noreads {
return nil
}
// Ensure the subfetcher is still alive
select {
case <-p.term:
return errTerminated
default:
}
id := p.trieID(owner, root)
fetcher := p.fetchers[id]
if fetcher == nil {
fetcher = newSubfetcher(p.db, p.root, owner, root, addr)
p.fetchers[id] = fetcher
}
return fetcher.schedule(keys, read)
}
// trie returns the trie matching the root hash, blocking until the fetcher of
// the given trie terminates. If no fetcher exists for the request, nil will be
// returned.
func (p *triePrefetcher) trie(owner common.Hash, root common.Hash) Trie {
// Bail if no trie was prefetched for this root
fetcher := p.fetchers[p.trieID(owner, root)]
if fetcher == nil {
log.Error("Prefetcher missed to load trie", "owner", owner, "root", root)
p.deliveryMissMeter.Mark(1)
return nil
}
// Subfetcher exists, retrieve its trie
return fetcher.peek()
}
// used marks a batch of state items used to allow creating statistics as to
// how useful or wasteful the fetcher is.
func (p *triePrefetcher) used(owner common.Hash, root common.Hash, used [][]byte) {
if fetcher := p.fetchers[p.trieID(owner, root)]; fetcher != nil {
fetcher.wait() // ensure the fetcher's idle before poking in its internals
fetcher.used = used
}
}
// trieID returns an unique trie identifier consists the trie owner and root hash.
func (p *triePrefetcher) trieID(owner common.Hash, root common.Hash) string {
trieID := make([]byte, common.HashLength*2)
copy(trieID, owner.Bytes())
copy(trieID[common.HashLength:], root.Bytes())
return string(trieID)
}
// subfetcher is a trie fetcher goroutine responsible for pulling entries for a
// single trie. It is spawned when a new root is encountered and lives until the
// main prefetcher is paused and either all requested items are processed or if
// the trie being worked on is retrieved from the prefetcher.
type subfetcher struct {
db Database // Database to load trie nodes through
state common.Hash // Root hash of the state to prefetch
owner common.Hash // Owner of the trie, usually account hash
root common.Hash // Root hash of the trie to prefetch
addr common.Address // Address of the account that the trie belongs to
trie Trie // Trie being populated with nodes
tasks []*subfetcherTask // Items queued up for retrieval
lock sync.Mutex // Lock protecting the task queue
wake chan struct{} // Wake channel if a new task is scheduled
stop chan struct{} // Channel to interrupt processing
term chan struct{} // Channel to signal interruption
seenRead map[string]struct{} // Tracks the entries already loaded via read operations
seenWrite map[string]struct{} // Tracks the entries already loaded via write operations
dupsRead int // Number of duplicate preload tasks via reads only
dupsWrite int // Number of duplicate preload tasks via writes only
dupsCross int // Number of duplicate preload tasks via read-write-crosses
used [][]byte // Tracks the entries used in the end
}
// subfetcherTask is a trie path to prefetch, tagged with whether it originates
// from a read or a write request.
type subfetcherTask struct {
read bool
key []byte
}
// newSubfetcher creates a goroutine to prefetch state items belonging to a
// particular root hash.
func newSubfetcher(db Database, state common.Hash, owner common.Hash, root common.Hash, addr common.Address) *subfetcher {
sf := &subfetcher{
db: db,
state: state,
owner: owner,
root: root,
addr: addr,
wake: make(chan struct{}, 1),
stop: make(chan struct{}),
term: make(chan struct{}),
seenRead: make(map[string]struct{}),
seenWrite: make(map[string]struct{}),
}
go sf.loop()
return sf
}
// schedule adds a batch of trie keys to the queue to prefetch.
func (sf *subfetcher) schedule(keys [][]byte, read bool) error {
// Ensure the subfetcher is still alive
select {
case <-sf.term:
return errTerminated
default:
}
// Append the tasks to the current queue
sf.lock.Lock()
for _, key := range keys {
key := key // closure for the append below
sf.tasks = append(sf.tasks, &subfetcherTask{read: read, key: key})
}
sf.lock.Unlock()
// Notify the background thread to execute scheduled tasks
select {
case sf.wake <- struct{}{}:
// Wake signal sent
default:
// Wake signal not sent as a previous one is already queued
}
return nil
}
// wait blocks until the subfetcher terminates. This method is used to block on
// an async termination before accessing internal fields from the fetcher.
func (sf *subfetcher) wait() {
<-sf.term
}
// peek retrieves the fetcher's trie, populated with any pre-fetched data. The
// returned trie will be a shallow copy, so modifying it will break subsequent
// peeks for the original data. The method will block until all the scheduled
// data has been loaded and the fethcer terminated.
func (sf *subfetcher) peek() Trie {
// Block until the fetcher terminates, then retrieve the trie
sf.wait()
return sf.trie
}
// terminate requests the subfetcher to stop accepting new tasks and spin down
// as soon as everything is loaded. Depending on the async parameter, the method
// will either block until all disk loads finish or return immediately.
func (sf *subfetcher) terminate(async bool) {
select {
case <-sf.stop:
default:
close(sf.stop)
}
if async {
return
}
<-sf.term
}
// loop loads newly-scheduled trie tasks as they are received and loads them, stopping
// when requested.
func (sf *subfetcher) loop() {
// No matter how the loop stops, signal anyone waiting that it's terminated
defer close(sf.term)
// Start by opening the trie and stop processing if it fails
if sf.owner == (common.Hash{}) {
trie, err := sf.db.OpenTrie(sf.root)
if err != nil {
log.Warn("Trie prefetcher failed opening trie", "root", sf.root, "err", err)
return
}
sf.trie = trie
} else {
trie, err := sf.db.OpenStorageTrie(sf.state, sf.addr, sf.root, nil)
if err != nil {
log.Warn("Trie prefetcher failed opening trie", "root", sf.root, "err", err)
return
}
sf.trie = trie
}
// Trie opened successfully, keep prefetching items
for {
select {
case <-sf.wake:
// Execute all remaining tasks in a single run
sf.lock.Lock()
tasks := sf.tasks
sf.tasks = nil
sf.lock.Unlock()
for _, task := range tasks {
key := string(task.key)
if task.read {
if _, ok := sf.seenRead[key]; ok {
sf.dupsRead++
continue
}
if _, ok := sf.seenWrite[key]; ok {
sf.dupsCross++
continue
}
} else {
if _, ok := sf.seenRead[key]; ok {
sf.dupsCross++
continue
}
if _, ok := sf.seenWrite[key]; ok {
sf.dupsWrite++
continue
}
}
if len(task.key) == common.AddressLength {
sf.trie.GetAccount(common.BytesToAddress(task.key))
} else {
sf.trie.GetStorage(sf.addr, task.key)
}
if task.read {
sf.seenRead[key] = struct{}{}
} else {
sf.seenWrite[key] = struct{}{}
}
}
case <-sf.stop:
// Termination is requested, abort if no more tasks are pending. If
// there are some, exhaust them first.
sf.lock.Lock()
done := sf.tasks == nil
sf.lock.Unlock()
if done {
return
}
// Some tasks are pending, loop and pick them up (that wake branch
// will be selected eventually, whilst stop remains closed to this
// branch will also run afterwards).
}
}
}