mirror of
https://github.com/ethereum/go-ethereum.git
synced 2026-07-27 15:16:43 +00:00
eth/downloader: fix state request leak
This commit fixes the hang seen sometimes while doing the state sync. The cause of the hang was a rare combination of events: request state data from peer, peer drops and reconnects almost immediately. This caused a new download task to be assigned to the peer, overwriting the old one still waiting for a timeout, which in turned leaked the requests out, never to be retried. The fix is to ensure that a task assignment moves any pending one back into the retry queue. The commit also fixes a regression with peer dropping due to stalls. The current code considered a peer stalling if they timed out delivering 1 item. However, the downloader never requests only one, the minimum is 2 (attempt to fine tune estimated latency/bandwidth). The fix is simply to drop if a timeout is detected at 2 items. Apart from the above bugfixes, the commit contains some code polishes I made while debugging the hang.
This commit is contained in:
Péter Szilágyi
parent
e3717b48c3
commit
115768a660
1 changed files with 138 additions and 86 deletions
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@ -30,19 +30,24 @@ import (
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"github.com/ethereum/go-ethereum/trie"
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)
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// stateReq represents a batch of state fetch requests groupped together into
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// a single data retrieval network packet.
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type stateReq struct {
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items []common.Hash
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tasks map[common.Hash]*stateTask
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timeout time.Duration
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timer *time.Timer // fires when timeout has elapsed
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peer *peer // the peer that we're requesting from
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response [][]byte // the response. this is nil for timed-out requests.
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items []common.Hash // Hashes of the state items to download
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tasks map[common.Hash]*stateTask // Download tasks to track previous attempts
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timeout time.Duration // Maximum round trip time for this to complete
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timer *time.Timer // Timer to fire when the RTT timeout expires
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peer *peer // Peer that we're requesting from
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response [][]byte // Response data of the peer (nil for timeouts)
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}
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// timedOut returns if this request timed out.
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func (req *stateReq) timedOut() bool {
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return req.response == nil
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}
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// stateSyncStats is a collection of progress stats to report during a state trie
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// sync to RPC requests as well as to display in user logs.
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type stateSyncStats struct {
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processed uint64 // Number of state entries processed
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duplicate uint64 // Number of state entries downloaded twice
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@ -50,7 +55,7 @@ type stateSyncStats struct {
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pending uint64 // Number of still pending state entries
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}
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// syncPivotState starts downloading state with the given root hash.
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// syncState starts downloading state with the given root hash.
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func (d *Downloader) syncState(root common.Hash) *stateSync {
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s := newStateSync(d, root)
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select {
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@ -79,19 +84,20 @@ func (d *Downloader) stateFetcher() {
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}
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}
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// runStateSync runs s until it completes or another stateSync is requested.
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// runStateSync runs a state synchronisation until it completes or another root
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// hash is requested to be switched over to.
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func (d *Downloader) runStateSync(s *stateSync) *stateSync {
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var (
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activeReqs = make(map[string]*stateReq)
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finishedReqs []*stateReq
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timeout = make(chan *stateReq)
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active = make(map[string]*stateReq) // Currently in-flight requests
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finished []*stateReq // Completed or failed requests
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timeout = make(chan *stateReq) // Timed out active requests
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)
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defer func() {
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// Cancel active request timers on exit. Also set peers to idle so they're
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// available for the next sync.
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for _, req := range activeReqs {
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for _, req := range active {
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req.timer.Stop()
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req.peer.SetNodeDataIdle(0)
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req.peer.SetNodeDataIdle(len(req.items))
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}
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}()
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// Run the state sync.
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@ -100,10 +106,12 @@ func (d *Downloader) runStateSync(s *stateSync) *stateSync {
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for {
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// Enable sending of the first buffered element if there is one.
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var deliverReq *stateReq
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var deliverReqCh chan *stateReq
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if len(finishedReqs) > 0 {
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deliverReq = finishedReqs[0]
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var (
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deliverReq *stateReq
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deliverReqCh chan *stateReq
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)
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if len(finished) > 0 {
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deliverReq = finished[0]
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deliverReqCh = s.deliver
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}
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@ -111,36 +119,56 @@ func (d *Downloader) runStateSync(s *stateSync) *stateSync {
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// The stateSync lifecycle:
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case next := <-d.stateSyncStart:
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return next
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case <-s.done:
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return nil
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// Send the next finished request to the current sync:
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case deliverReqCh <- deliverReq:
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finishedReqs = append(finishedReqs[:0], finishedReqs[1:]...)
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finished = append(finished[:0], finished[1:]...)
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// Handle incoming state packs:
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case pack := <-d.stateCh:
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req := activeReqs[pack.PeerId()]
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// Discard any data not requested (or previsouly timed out)
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req := active[pack.PeerId()]
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if req == nil {
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log.Debug("Unrequested node data", "peer", pack.PeerId(), "len", pack.Items())
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continue
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}
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delete(activeReqs, pack.PeerId())
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// Finalize the request and queue up for processing
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req.timer.Stop()
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req.response = pack.(*statePack).states
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finishedReqs = append(finishedReqs, req)
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finished = append(finished, req)
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delete(active, pack.PeerId())
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// Handle timed-out requests:
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case req := <-timeout:
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if activeReqs[req.peer.id] != req {
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continue // ignore old timeout
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// If the peer is already requesting something else, ignore the stale timeout.
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// This can happen when the timeout and the delivery happens simultaneously,
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// causing both pathways to trigger.
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if active[req.peer.id] != req {
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continue
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}
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finishedReqs = append(finishedReqs, req)
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delete(activeReqs, req.peer.id)
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// Move the timed out data back into the download queue
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finished = append(finished, req)
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delete(active, req.peer.id)
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// Track outgoing state requests:
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case req := <-d.trackStateReq:
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activeReqs[req.peer.id] = req
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// If an active request already exists for this peer, we have a problem. In
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// theory the trie node schedule must never assign two requests to the same
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// peer. In practive however, a peer might receive a request, disconnect and
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// immediately reconnect before the previous times out. In this case the first
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// request is never honored, alas we must not silently overwrite it, as that
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// causes valid requests to go missing and sync to get stuck.
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if old := active[req.peer.id]; old != nil {
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log.Warn("Busy peer assigned new state fetch", "peer", old.peer.id)
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// Make sure the previous one doesn't get siletly lost
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finished = append(finished, old)
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}
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// Start a timer to notify the sync loop if the peer stalled.
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req.timer = time.AfterFunc(req.timeout, func() {
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select {
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case timeout <- req:
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@ -149,41 +177,55 @@ func (d *Downloader) runStateSync(s *stateSync) *stateSync {
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// timer is fired just before exiting runStateSync.
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}
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})
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active[req.peer.id] = req
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}
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}
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}
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// stateSync schedules requests for downloading a particular state root.
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// stateSync schedules requests for downloading a particular state trie defined
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// by a given state root.
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type stateSync struct {
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d *Downloader
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sched *state.StateSync
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keccak hash.Hash
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tasksAvailable map[common.Hash]*stateTask
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d *Downloader // Downloader instance to access and manage current peerset
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deliver chan *stateReq
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cancel chan struct{}
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cancelOnce sync.Once
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done chan struct{}
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err error // set after done is closed
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sched *state.StateSync // State trie sync scheduler defining the tasks
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keccak hash.Hash // Keccak256 hasher to verify deliveries with
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tasks map[common.Hash]*stateTask // Set of tasks currently queued for retrieval
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deliver chan *stateReq // Delivery channel multiplexing peer responses
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cancel chan struct{} // Channel to signal a termination request
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cancelOnce sync.Once // Ensures cancel only ever gets called once
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done chan struct{} // Channel to signal termination completion
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err error // Any error hit during sync (set before completion)
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}
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// stateTask represents a single trie node download taks, containing a set of
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// peers already attempted retrieval from to detect stalled syncs and abort.
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type stateTask struct {
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triedPeers map[string]struct{}
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numTries int
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attempts map[string]struct{}
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}
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// newStateSync creates a new state trie download scheduler. This method does not
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// yet start the sync. The user needs to call run to initiate.
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func newStateSync(d *Downloader, root common.Hash) *stateSync {
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return &stateSync{
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d: d,
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sched: state.NewStateSync(root, d.stateDB),
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keccak: sha3.NewKeccak256(),
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tasksAvailable: make(map[common.Hash]*stateTask),
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deliver: make(chan *stateReq),
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cancel: make(chan struct{}),
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done: make(chan struct{}, 1),
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d: d,
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sched: state.NewStateSync(root, d.stateDB),
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keccak: sha3.NewKeccak256(),
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tasks: make(map[common.Hash]*stateTask),
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deliver: make(chan *stateReq),
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cancel: make(chan struct{}),
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done: make(chan struct{}),
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}
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}
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// run starts the task assignment and response processing loop, blocking until
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// it finishes, and finally notifying any goroutines waiting for the loop to
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// finish.
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func (s *stateSync) run() {
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s.err = s.loop()
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close(s.done)
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}
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// Wait blocks until the sync is done or canceled.
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func (s *stateSync) Wait() error {
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<-s.done
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@ -196,31 +238,38 @@ func (s *stateSync) Cancel() error {
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return s.Wait()
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}
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func (s *stateSync) run() {
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s.err = s.loop()
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close(s.done)
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}
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// loop is the main event loop of a state trie sync. It it responsible for the
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// assignment of new tasks to peers (including sending it to them) as well as
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// for the processing of inbound data. Note, that the loop does not directly
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// receive data from peers, rather those are buffered up in the downloader and
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// pushed here async. The reason is to decouple processing from data receipt
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// and timeouts.
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func (s *stateSync) loop() error {
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newPeer := make(chan *peer, 200)
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// Listen for new peer events to assign tasks to them
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newPeer := make(chan *peer, 1024)
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peerSub := s.d.peers.SubscribeNewPeers(newPeer)
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defer peerSub.Unsubscribe()
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// Keep assigning new tasks until the sync completes or aborts
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for s.sched.Pending() > 0 {
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if err := s.assignTasks(); err != nil {
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return err
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}
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// Tasks assigned, wait for something to happen
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select {
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case <-newPeer:
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// assign new tasks
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// New peer arrived, try to assign it download tasks
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case <-s.cancel:
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return errCancelStateFetch
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case req := <-s.deliver:
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// Response or timeout triggered, drop the peer if stalling
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log.Trace("Received node data response", "peer", req.peer.id, "count", len(req.response), "timeout", req.timedOut())
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if len(req.items) == 1 && req.timedOut() {
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log.Warn("Node data timeout, dropping peer", "peer", req.peer.id)
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if len(req.items) <= 2 && req.timedOut() {
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// 2 items are the minimum requested, if even that times out, we've no use of
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// this peer at the moment.
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log.Warn("Stalling state sync, dropping peer", "peer", req.peer.id)
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s.d.dropPeer(req.peer.id)
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}
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// Process all the received blobs and check for stale delivery
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@ -238,56 +287,59 @@ func (s *stateSync) loop() error {
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return nil
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}
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func (s *stateSync) sendReq(req *stateReq) {
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req.peer.log.Trace("Requesting new batch of data", "type", "state", "count", len(req.items))
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select {
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case s.d.trackStateReq <- req:
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req.peer.FetchNodeData(req.items)
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case <-s.cancel:
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}
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}
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// assignTasks attempts to assing new tasks to all idle peers, either from the
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// batch currently being retried, or fetching new data from the trie sync itself.
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func (s *stateSync) assignTasks() error {
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// Iterate over all idle peers and try to assign them state fetches
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peers, _ := s.d.peers.NodeDataIdlePeers()
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for _, p := range peers {
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// Assign a batch of fetches proportional to the estimated latency/bandwidth
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cap := p.NodeDataCapacity(s.d.requestRTT())
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req := &stateReq{peer: p, timeout: s.d.requestTTL()}
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if err := s.popTasks(cap, req); err != nil {
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return err
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}
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s.fillTasks(cap, req)
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// If the peer was assigned tasks to fetch, send the network request
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if len(req.items) > 0 {
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s.sendReq(req)
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req.peer.log.Trace("Requesting new batch of data", "type", "state", "count", len(req.items))
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select {
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case s.d.trackStateReq <- req:
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req.peer.FetchNodeData(req.items)
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case <-s.cancel:
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}
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}
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}
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return nil
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}
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func (s *stateSync) popTasks(n int, req *stateReq) error {
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// fillTasks fills the given request object with a maximum of n state download
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// tasks to send to the remote peer.
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func (s *stateSync) fillTasks(n int, req *stateReq) {
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// Refill available tasks from the scheduler.
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if len(s.tasksAvailable) < n {
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new := s.sched.Missing(n - len(s.tasksAvailable))
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if len(s.tasks) < n {
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new := s.sched.Missing(n - len(s.tasks))
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for _, hash := range new {
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s.tasksAvailable[hash] = &stateTask{make(map[string]struct{}), 0}
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s.tasks[hash] = &stateTask{make(map[string]struct{})}
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}
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}
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// Find tasks that haven't been tried with the request's peer.
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req.items = make([]common.Hash, 0, n)
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req.tasks = make(map[common.Hash]*stateTask, n)
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for hash, t := range s.tasksAvailable {
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for hash, t := range s.tasks {
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// Stop when we've gathered enough requests
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if len(req.items) == n {
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break
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}
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if _, ok := t.triedPeers[req.peer.id]; ok {
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// Skip any requests we've already tried from this peer
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if _, ok := t.attempts[req.peer.id]; ok {
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continue
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}
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t.triedPeers[req.peer.id] = struct{}{}
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t.numTries++
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// Assign the request to this peer
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t.attempts[req.peer.id] = struct{}{}
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req.items = append(req.items, hash)
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req.tasks[hash] = t
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delete(s.tasksAvailable, hash)
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delete(s.tasks, hash)
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}
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return nil
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}
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// process iterates over a batch of delivered state data, injecting each item
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@ -340,22 +392,22 @@ func (s *stateSync) process(req *stateReq) (bool, error) {
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// limit or a previous timeout + delayed delivery. Both cases should permit
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// the node to retry the missing items (to avoid single-peer stalls).
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if len(req.response) > 0 || req.timedOut() {
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delete(task.triedPeers, req.peer.id)
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delete(task.attempts, req.peer.id)
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}
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// If we've requested the node too many times already, it may be a malicious
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// sync where nobody has the right data. Abort.
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if len(task.triedPeers) >= npeers {
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return stale, fmt.Errorf("state node %s failed with all peers (%d tries, %d peers)", hash.TerminalString(), len(task.triedPeers), npeers)
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if len(task.attempts) >= npeers {
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return stale, fmt.Errorf("state node %s failed with all peers (%d tries, %d peers)", hash.TerminalString(), len(task.attempts), npeers)
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}
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// Missing item, place into the retry queue.
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s.tasksAvailable[hash] = task
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s.tasks[hash] = task
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}
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return stale, nil
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}
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// processNodeData tries to inject a trie node data blob delivered from a remote
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// peer into te state trie, returning whether anything useful was written or any
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// error occured.
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// peer into the state trie, returning whether anything useful was written or any
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// error occurred.
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func (s *stateSync) processNodeData(blob []byte) (bool, common.Hash, error) {
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// Convert the delivered data blob into a trie sync result
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res := trie.SyncResult{Data: blob}
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@ -387,5 +439,5 @@ func (s *stateSync) updateStats(processed, duplicate, unexpected int, duration t
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s.d.syncStatsState.duplicate += uint64(duplicate)
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s.d.syncStatsState.unexpected += uint64(unexpected)
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log.Info("Imported new state entries", "count", processed, "elapsed", common.PrettyDuration(duration), "processed", s.d.syncStatsState.processed, "pending", s.d.syncStatsState.pending, "retry", len(s.tasksAvailable), "duplicate", s.d.syncStatsState.duplicate, "unexpected", s.d.syncStatsState.unexpected)
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log.Info("Imported new state entries", "count", processed, "elapsed", common.PrettyDuration(duration), "processed", s.d.syncStatsState.processed, "pending", s.d.syncStatsState.pending, "retry", len(s.tasks), "duplicate", s.d.syncStatsState.duplicate, "unexpected", s.d.syncStatsState.unexpected)
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}
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