/
trie_segments.go
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/
trie_segments.go
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// (c) 2021-2022, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package statesync
import (
"bytes"
"context"
"encoding/binary"
"fmt"
"sync"
"github.com/ava-labs/avalanchego/utils/wrappers"
"github.com/ava-labs/subnet-evm/core/rawdb"
syncclient "github.com/ava-labs/subnet-evm/sync/client"
"github.com/ava-labs/subnet-evm/trie"
"github.com/ava-labs/subnet-evm/utils"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/ethdb"
"github.com/ethereum/go-ethereum/log"
)
var (
_ syncclient.LeafSyncTask = &trieSegment{}
_ fmt.Stringer = &trieSegment{}
)
// trieToSync keeps the state of a single trie syncing
// this can be a storage or the main trie.
type trieToSync struct {
root common.Hash
account common.Hash
// The trie consists of a slice of segments. each
// segment has a start and end range of keys, and
// contains a pointer back to this struct.
segments []*trieSegment
// These fields are used to hash the segments in
// order, even though they may finish syncing out
// of order or concurrently.
lock sync.Mutex
segmentsDone map[int]struct{}
segmentToHashNext int
// We use a stack trie to hash the leafs and have
// a batch used for writing it to disk.
batch ethdb.Batch
stackTrie *trie.StackTrie
// We keep a pointer to the overall sync operation,
// used to add segments to the work queue and to
// update the eta.
sync *stateSync
// task implements the syncTask interface with methods
// containing logic specific to the main trie or storage
// tries.
task syncTask
isMainTrie bool
}
// NewTrieToSync initializes a trieToSync and restores any previously started segments.
func NewTrieToSync(sync *stateSync, root common.Hash, account common.Hash, syncTask syncTask) (*trieToSync, error) {
batch := sync.db.NewBatch() // TODO: migrate state sync to use database schemes.
writeFn := func(owner common.Hash, path []byte, hash common.Hash, blob []byte) {
rawdb.WriteTrieNode(batch, owner, path, hash, blob, rawdb.HashScheme)
}
trieToSync := &trieToSync{
sync: sync,
root: root,
account: account,
batch: batch,
stackTrie: trie.NewStackTrie(writeFn),
isMainTrie: (root == sync.root),
task: syncTask,
segmentsDone: make(map[int]struct{}),
}
return trieToSync, trieToSync.loadSegments()
}
// loadSegments reads persistent storage and initializes trieSegments that
// had been previously started and need to be resumed.
func (t *trieToSync) loadSegments() error {
// Get an iterator for segments for t.root and see if we find anything.
// This lets us check if this trie was previously segmented, in which
// case we need to restore the same segments on resume.
it := rawdb.NewSyncSegmentsIterator(t.sync.db, t.root)
defer it.Release()
// Track the previously added segment as we loop over persisted values.
var prevSegmentStart []byte
for it.Next() {
// If we find any persisted segments with the specified
// prefix, we add a new segment to the trie here.
// The segment we add represents a segment ending at the
// key immediately prior to the segment we found on disk.
// This is because we do not persist the beginning of
// the first segment.
_, segmentStart := rawdb.UnpackSyncSegmentKey(it.Key())
segmentStartPos := binary.BigEndian.Uint16(segmentStart[:wrappers.ShortLen])
t.addSegment(prevSegmentStart, addPadding(segmentStartPos-1, 0xff))
// keep tracking the previous segment
prevSegmentStart = segmentStart
}
if err := it.Error(); err != nil {
return err
}
// this creates the last segment if any were found in the loop
// and also handles the case where there were no segments persisted to disk.
t.addSegment(prevSegmentStart, nil)
for _, segment := range t.segments {
// for each segment we need to find the last key already persisted
// so syncing can begin at the subsequent key
var lastKey []byte
it := segment.trie.task.IterateLeafs(common.BytesToHash(segment.start))
defer it.Release()
for it.Next() {
if len(segment.end) > 0 && bytes.Compare(it.Key(), segment.end) > 0 {
// don't go past the end of the segment
break
}
lastKey = common.CopyBytes(it.Key())
segment.leafs++
}
if lastKey != nil {
utils.IncrOne(lastKey)
segment.pos = lastKey // syncing will start from this key
}
log.Debug("statesync: loading segment", "segment", segment)
}
return it.Error()
}
// startSyncing adds the trieToSync's segments to the work queue
func (t *trieToSync) startSyncing() {
for _, segment := range t.segments {
t.sync.segments <- segment // this will queue the segment for syncing
}
}
// addSegment appends a newly created segment specified by [start] and
// [end] to [t.segments] and returns it.
// note: addSegment does not take a lock and therefore is called only
// before multiple segments are syncing concurrently.
func (t *trieToSync) addSegment(start, end []byte) *trieSegment {
segment := &trieSegment{
start: start,
end: end,
trie: t,
idx: len(t.segments),
batch: t.sync.db.NewBatch(),
}
t.segments = append(t.segments, segment)
return segment
}
// segmentFinished is called when one the trie segment with index [idx] finishes syncing.
// creates intermediary hash nodes for the trie up to the last contiguous segment received from start.
func (t *trieToSync) segmentFinished(ctx context.Context, idx int) error {
t.lock.Lock()
defer t.lock.Unlock()
log.Debug("statesync: segment finished", "segment", t.segments[idx])
t.segmentsDone[idx] = struct{}{}
for {
if _, ok := t.segmentsDone[t.segmentToHashNext]; !ok {
// if not the next contiguous segment from the beginning of the trie
// don't do anything.
break
}
segment := t.segments[t.segmentToHashNext]
// persist any items in the batch as they will be iterated below.
if err := segment.batch.Write(); err != nil {
return err
}
segment.batch.Reset() // reset the batch to free memory (even though it is no longer used)
// iterate all the items from the start of the segment (end is checked in the loop)
it := t.task.IterateLeafs(common.BytesToHash(segment.start))
defer it.Release()
for it.Next() {
if err := ctx.Err(); err != nil {
return err
}
if len(segment.end) > 0 && bytes.Compare(it.Key(), segment.end) > 0 {
// don't go past the end of the segment. (data belongs to the next segment)
break
}
// update the stack trie and cap the batch it writes to.
value := common.CopyBytes(it.Value())
if err := t.stackTrie.Update(it.Key(), value); err != nil {
return err
}
if t.batch.ValueSize() > t.sync.batchSize {
if err := t.batch.Write(); err != nil {
return err
}
t.batch.Reset()
}
}
if err := it.Error(); err != nil {
return err
}
t.segmentToHashNext++
}
if t.segmentToHashNext < len(t.segments) {
// trie not complete
return nil
}
// when the trie is finished, this hashes any remaining nodes in the stack
// trie and creates the root
actualRoot, err := t.stackTrie.Commit()
if err != nil {
return err
}
if actualRoot != t.root {
return fmt.Errorf("unexpected root, expected=%s, actual=%s, account=%s", t.root, actualRoot, t.account)
}
if !t.isMainTrie {
// the batch containing the main trie's root will be committed on
// sync completion.
if err := t.batch.Write(); err != nil {
return err
}
}
// remove all segments for this root from persistent storage
if err := rawdb.ClearSyncSegments(t.sync.db, t.root); err != nil {
return err
}
return t.task.OnFinish()
}
// createSegmentsIfNeeded is called from the leaf handler. In case the trie syncing only has
// one segment but a large number of leafs ([t.estimateSize() > segmentThreshold], it will
// create [numSegments-1] additional segments to sync the trie.
func (t *trieToSync) createSegmentsIfNeeded(numSegments int) error {
if !t.shouldSegment() {
return nil
}
return t.createSegments(numSegments)
}
// shouldSegment returns true if a trie should be separated into segments.
func (t *trieToSync) shouldSegment() bool {
t.lock.Lock()
defer t.lock.Unlock()
// Return false if the trie has already been segmented.
if len(t.segments) > 1 {
return false
}
// Return true iff the estimated size of the trie exceeds [segmentThreshold].
// Note: at this point there is only a single segment (loadSegments guarantees there
// is at least one segment).
segment := t.segments[0]
return segment.estimateSize() >= uint64(segmentThreshold)
}
// divide the key space into [numSegments] consecutive segments.
// we use 2 bytes to build the ranges and fill the rest with
// ones or zeroes accordingly.
// this represents the step between the first 2 bytes of the start
// key of consecutive segments.
// createSegments should only be called once when there is only one
// thread accessing this trie, such that there is no need to hold a lock.
func (t *trieToSync) createSegments(numSegments int) error {
segment := t.segments[0]
segmentStep := 0x10000 / numSegments
for i := 0; i < numSegments; i++ {
start := uint16(i * segmentStep)
end := uint16(i*segmentStep + (segmentStep - 1))
startBytes := addPadding(start, 0x00)
endBytes := addPadding(end, 0xff)
// Skip any portion of the trie that has already been synced.
if bytes.Compare(segment.pos, endBytes) >= 0 {
continue
}
// since the first segment is already syncing,
// it does not need to be added to the task queue.
// instead, we update its end and move on to creating
// the next segment
if segment.end == nil {
segment.end = endBytes
continue
}
// create the segments
segment := t.addSegment(startBytes, endBytes)
if err := rawdb.WriteSyncSegment(t.sync.db, t.root, segment.start); err != nil {
return err
}
}
// add the newly created segments to the task queue
// after creating them. We skip the first one, as it
// is already syncing.
// this avoids concurrent access to [t.segments].
for i := 1; i < len(t.segments); i++ {
t.sync.segments <- t.segments[i]
}
t.sync.stats.incTriesSegmented()
log.Debug("statesync: trie segmented for parallel sync", "root", t.root, "account", t.account, "segments", len(t.segments))
return nil
}
// trieSegment keeps the state of syncing one segment of a [trieToSync]
// struct and keeps a pointer to the [trieToSync] it is syncing.
// each trieSegment is accessed by its own goroutine, so locks are not
// needed to access its fields
type trieSegment struct {
start []byte
pos []byte
end []byte
trie *trieToSync // points back to the trie the segment belongs to
idx int // index of this segment in the trie's segment slice
batch ethdb.Batch // batch for writing leafs to
leafs uint64 // number of leafs added to the segment
}
func (t *trieSegment) String() string {
return fmt.Sprintf(
"[%s](%d/%d) (start=%s,end=%s)",
t.trie.root, t.idx+1, len(t.trie.segments),
common.BytesToHash(t.start).TerminalString(),
common.BytesToHash(t.end).TerminalString(),
)
}
// these functions implement the LeafSyncTask interface.
func (t *trieSegment) Root() common.Hash { return t.trie.root }
func (t *trieSegment) Account() common.Hash { return t.trie.account }
func (t *trieSegment) End() []byte { return t.end }
func (t *trieSegment) OnStart() (bool, error) { return t.trie.task.OnStart() }
func (t *trieSegment) OnFinish(ctx context.Context) error { return t.trie.segmentFinished(ctx, t.idx) }
func (t *trieSegment) Start() []byte {
if t.pos != nil {
return t.pos
}
return t.start
}
func (t *trieSegment) OnLeafs(keys, vals [][]byte) error {
// invoke the onLeafs callback
if err := t.trie.task.OnLeafs(t.batch, keys, vals); err != nil {
return err
}
// cap the segment's batch
if t.batch.ValueSize() > t.trie.sync.batchSize {
if err := t.batch.Write(); err != nil {
return err
}
t.batch.Reset()
}
t.leafs += uint64(len(keys))
if len(keys) > 0 {
t.pos = keys[len(keys)-1] // remember the position, used in estimating trie size
utils.IncrOne(t.pos)
}
// update eta
t.trie.sync.stats.incLeafs(t, uint64(len(keys)), t.estimateSize())
if t.trie.root == t.trie.sync.root {
return t.trie.createSegmentsIfNeeded(numMainTrieSegments)
} else {
return t.trie.createSegmentsIfNeeded(numStorageTrieSegments)
}
}
// estimateSize calculates an estimate of the number of leafs and returns it,
// this assumes the trie has uniform key density.
// Note: returns 0 if there has been no progress in syncing the trie.
func (t *trieSegment) estimateSize() uint64 {
start, pos, end := uint16(0), uint16(0), uint16(0xffff)
if len(t.start) > 0 {
start = binary.BigEndian.Uint16(t.start)
}
if len(t.pos) > 0 {
pos = binary.BigEndian.Uint16(t.pos)
}
if len(t.end) > 0 {
end = binary.BigEndian.Uint16(t.end)
}
progress := pos - start
if progress == 0 {
// this should not occur since estimateSize is called after processing
// a batch of leafs, which sets [pos].
// avoid division by 0 out of caution.
return 0
}
left := end - pos
return t.leafs * uint64(left) / uint64(progress)
}
// addPadding returns a []byte of length [common.Hash], starting with the BigEndian
// representation of [pos], and the rest filled with [padding].
func addPadding(pos uint16, padding byte) []byte {
packer := wrappers.Packer{Bytes: make([]byte, common.HashLength)}
packer.PackShort(pos)
packer.PackFixedBytes(bytes.Repeat([]byte{padding}, common.HashLength-wrappers.ShortLen))
return packer.Bytes
}