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core: improve chain rewinding mechanism #29196

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merged 12 commits into from
Mar 13, 2024
Merged

core: improve chain rewinding mechanism #29196

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2f0f190
core: improve chain rewinding mechanism
rjl493456442 Mar 8, 2024
d131a95
core: address comment
rjl493456442 Mar 11, 2024
88a6dc8
core: periodically print progress log
rjl493456442 Mar 11, 2024
9d7a4db
core: address comments
rjl493456442 Mar 11, 2024
470916d
core: fix comment
rjl493456442 Mar 11, 2024
c6b0eb7
core: fix rewinding in path
rjl493456442 Mar 11, 2024
60fb704
core: fix beyondRoot condition
rjl493456442 Mar 11, 2024
b5df29c
core: polish code
rjl493456442 Mar 11, 2024
e3884f1
core: polish code
rjl493456442 Mar 11, 2024
3784c6c
core: extend code comment
rjl493456442 Mar 11, 2024
ad7ac99
core: stop rewinding if chain is gapped or genesis is reached
rjl493456442 Mar 12, 2024
48bbb38
core: fix broken tests
rjl493456442 Mar 12, 2024
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238 changes: 183 additions & 55 deletions core/blockchain.go
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Original file line number Diff line number Diff line change
Expand Up @@ -616,6 +616,172 @@ func (bc *BlockChain) SetSafe(header *types.Header) {
}
}

// rewindPathHead implements the logic of rewindHead in the context of hash scheme.
func (bc *BlockChain) rewindHashHead(head *types.Header, root common.Hash) (*types.Header, uint64) {
var (
limit uint64 // The oldest block that will be searched for this rewinding
beyondRoot = root == common.Hash{} // Flag whether we're beyond the requested root (no root, always true)
pivot = rawdb.ReadLastPivotNumber(bc.db) // Associated block number of pivot point state
rootNumber uint64 // Associated block number of requested root

start = time.Now() // Timestamp the rewinding is restarted
logged = time.Now() // Timestamp last progress log was printed
)
// The oldest block to be searched is determined by the pivot block or a constant
// searching threshold. The rationale behind this is as follows:
//
// - Snap sync is selected if the pivot block is available. The earliest available
// state is the pivot block itself, so there is no sense in going further back.
//
// - Full sync is selected if the pivot block does not exist. The hash database
// periodically flushes the state to disk, and the used searching threshold is
// considered sufficient to find a persistent state, even for the testnet. It
// might be not enough for a chain that is nearly empty. In the worst case,
// the entire chain is reset to genesis, and snap sync is re-enabled on top,
// which is still acceptable.
if pivot != nil {
limit = *pivot
} else if head.Number.Uint64() > params.FullImmutabilityThreshold {
limit = head.Number.Uint64() - params.FullImmutabilityThreshold
}
for {
logger := log.Trace
if time.Since(logged) > time.Second*8 {
logged = time.Now()
logger = log.Info
}
logger("Block state missing, rewinding further", "number", head.Number, "hash", head.Hash(), "elapsed", common.PrettyDuration(time.Since(start)))

// If a root threshold was requested but not yet crossed, check
if !beyondRoot && head.Root == root {
beyondRoot, rootNumber = true, head.Number.Uint64()
}
// If search limit is reached, return the genesis block as the
// new chain head.
if head.Number.Uint64() < limit {
log.Info("Rewinding limit reached, resetting to genesis", "number", head.Number, "hash", head.Hash(), "limit", limit)
return bc.genesisBlock.Header(), rootNumber
}
// If the associated state is not reachable, continue searching
// backwards until an available state is found.
if !bc.HasState(head.Root) {
// If the chain is gapped in the middle, return the genesis
// block as the new chain head.
parent := bc.GetHeader(head.ParentHash, head.Number.Uint64()-1)
if parent == nil {
log.Error("Missing block in the middle, resetting to genesis", "number", head.Number.Uint64()-1, "hash", head.ParentHash)
return bc.genesisBlock.Header(), rootNumber
}
head = parent

// If the genesis block is reached, stop searching.
if head.Number.Uint64() == 0 {
log.Info("Genesis block reached", "number", head.Number, "hash", head.Hash())
return head, rootNumber
}
continue // keep rewinding
}
// Once the available state is found, ensure that the requested root
// has already been crossed. If not, continue rewinding.
if beyondRoot || head.Number.Uint64() == 0 {
log.Info("Rewound to block with state", "number", head.Number, "hash", head.Hash())
return head, rootNumber
}
log.Debug("Skipping block with threshold state", "number", head.Number, "hash", head.Hash(), "root", head.Root)
head = bc.GetHeader(head.ParentHash, head.Number.Uint64()-1) // Keep rewinding
}
}

// rewindPathHead implements the logic of rewindHead in the context of path scheme.
func (bc *BlockChain) rewindPathHead(head *types.Header, root common.Hash) (*types.Header, uint64) {
var (
pivot = rawdb.ReadLastPivotNumber(bc.db) // Associated block number of pivot block
rootNumber uint64 // Associated block number of requested root

// BeyondRoot represents whether the requested root is already
// crossed. The flag value is set to true if the root is empty.
beyondRoot = root == common.Hash{}

// noState represents if the target state requested for search
// is unavailable and impossible to be recovered.
noState = !bc.HasState(root) && !bc.stateRecoverable(root)

start = time.Now() // Timestamp the rewinding is restarted
logged = time.Now() // Timestamp last progress log was printed
)
// Rewind the head block tag until an available state is found.
for {
logger := log.Trace
if time.Since(logged) > time.Second*8 {
logged = time.Now()
logger = log.Info
}
logger("Block state missing, rewinding further", "number", head.Number, "hash", head.Hash(), "elapsed", common.PrettyDuration(time.Since(start)))

// If a root threshold was requested but not yet crossed, check
if !beyondRoot && head.Root == root {
beyondRoot, rootNumber = true, head.Number.Uint64()
}
// If the root threshold hasn't been crossed but the available
// state is reached, quickly determine if the target state is
// possible to be reached or not.
if !beyondRoot && noState && bc.HasState(head.Root) {
beyondRoot = true
log.Info("Disable the search for unattainable state", "root", root)
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Isn't this case the one where the snapshot persistent layer is below 90K? In the current implementation, won't we end up just having a broken snapshot layer that's always stale and the chain moving forward with the trie only? Shouldn't we trigger some snapshot-fixing in this case?

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Isn't this case the one where the snapshot persistent layer is below 90K?

True, the snapshot state is impossible to recover.

In this case, we will not search for the snapshot state, and return the block as the head with "first seen state".

won't we end up just having a broken snapshot layer that's always stale and the chain moving forward with the trie only?

We don't. As in this case, rootNumber is returned as 0, the snapshot recovery mechanism is disabled.

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But in that case, won't we simply leave the snapshot layer forever dangling in that old state?

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Ah, in case of a head mismatch, the snapshot gets invalidated and auto-regenerated?

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exactly

}
// Check if the associated state is available or recoverable if
// the requested root has already been crossed.
if beyondRoot && (bc.HasState(head.Root) || bc.stateRecoverable(head.Root)) {
break
}
// If pivot block is reached, return the genesis block as the
// new chain head. Theoretically there must be a persistent
// state before or at the pivot block, prevent endless rewinding
// towards the genesis just in case.
if pivot != nil && *pivot >= head.Number.Uint64() {
log.Info("Pivot block reached, resetting to genesis", "number", head.Number, "hash", head.Hash())
return bc.genesisBlock.Header(), rootNumber
}
// If the chain is gapped in the middle, return the genesis
// block as the new chain head
parent := bc.GetHeader(head.ParentHash, head.Number.Uint64()-1) // Keep rewinding
if parent == nil {
log.Error("Missing block in the middle, resetting to genesis", "number", head.Number.Uint64()-1, "hash", head.ParentHash)
return bc.genesisBlock.Header(), rootNumber
}
head = parent

// If the genesis block is reached, stop searching.
if head.Number.Uint64() == 0 {
log.Info("Genesis block reached", "number", head.Number, "hash", head.Hash())
return head, rootNumber
}
}
// Recover if the target state if it's not available yet.
if !bc.HasState(head.Root) {
if err := bc.triedb.Recover(head.Root); err != nil {
log.Crit("Failed to rollback state", "err", err)
}
}
log.Info("Rewound to block with state", "number", head.Number, "hash", head.Hash())
return head, rootNumber
}

// rewindHead searches the available states in the database and returns the associated
// block as the new head block.
//
// If the given root is not empty, then the rewind should attempt to pass the specified
// state root and return the associated block number as well. If the root, typically
// representing the state corresponding to snapshot disk layer, is deemed impassable,
// then block number zero is returned, indicating that snapshot recovery is disabled
// and the whole snapshot should be auto-generated in case of head mismatch.
func (bc *BlockChain) rewindHead(head *types.Header, root common.Hash) (*types.Header, uint64) {
if bc.triedb.Scheme() == rawdb.PathScheme {
return bc.rewindPathHead(head, root)
}
return bc.rewindHashHead(head, root)
}

// setHeadBeyondRoot rewinds the local chain to a new head with the extra condition
// that the rewind must pass the specified state root. This method is meant to be
// used when rewinding with snapshots enabled to ensure that we go back further than
Expand All @@ -634,79 +800,40 @@ func (bc *BlockChain) setHeadBeyondRoot(head uint64, time uint64, root common.Ha
}
defer bc.chainmu.Unlock()

// Track the block number of the requested root hash
var rootNumber uint64 // (no root == always 0)

// Retrieve the last pivot block to short circuit rollbacks beyond it and the
// current freezer limit to start nuking id underflown
pivot := rawdb.ReadLastPivotNumber(bc.db)
frozen, _ := bc.db.Ancients()
var (
// Track the block number of the requested root hash
rootNumber uint64 // (no root == always 0)

// Retrieve the last pivot block to short circuit rollbacks beyond it
// and the current freezer limit to start nuking it's underflown.
pivot = rawdb.ReadLastPivotNumber(bc.db)
)
updateFn := func(db ethdb.KeyValueWriter, header *types.Header) (*types.Header, bool) {
// Rewind the blockchain, ensuring we don't end up with a stateless head
// block. Note, depth equality is permitted to allow using SetHead as a
// chain reparation mechanism without deleting any data!
if currentBlock := bc.CurrentBlock(); currentBlock != nil && header.Number.Uint64() <= currentBlock.Number.Uint64() {
newHeadBlock := bc.GetBlock(header.Hash(), header.Number.Uint64())
if newHeadBlock == nil {
log.Error("Gap in the chain, rewinding to genesis", "number", header.Number, "hash", header.Hash())
newHeadBlock = bc.genesisBlock
} else {
// Block exists. Keep rewinding until either we find one with state
// or until we exceed the optional threshold root hash
beyondRoot := (root == common.Hash{}) // Flag whether we're beyond the requested root (no root, always true)

for {
// If a root threshold was requested but not yet crossed, check
if root != (common.Hash{}) && !beyondRoot && newHeadBlock.Root() == root {
beyondRoot, rootNumber = true, newHeadBlock.NumberU64()
}
if !bc.HasState(newHeadBlock.Root()) && !bc.stateRecoverable(newHeadBlock.Root()) {
log.Trace("Block state missing, rewinding further", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash())
if pivot == nil || newHeadBlock.NumberU64() > *pivot {
parent := bc.GetBlock(newHeadBlock.ParentHash(), newHeadBlock.NumberU64()-1)
if parent != nil {
newHeadBlock = parent
continue
}
log.Error("Missing block in the middle, aiming genesis", "number", newHeadBlock.NumberU64()-1, "hash", newHeadBlock.ParentHash())
newHeadBlock = bc.genesisBlock
} else {
log.Trace("Rewind passed pivot, aiming genesis", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash(), "pivot", *pivot)
newHeadBlock = bc.genesisBlock
}
}
if beyondRoot || newHeadBlock.NumberU64() == 0 {
if !bc.HasState(newHeadBlock.Root()) && bc.stateRecoverable(newHeadBlock.Root()) {
// Rewind to a block with recoverable state. If the state is
// missing, run the state recovery here.
if err := bc.triedb.Recover(newHeadBlock.Root()); err != nil {
log.Crit("Failed to rollback state", "err", err) // Shouldn't happen
}
log.Debug("Rewound to block with state", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash())
}
break
}
log.Debug("Skipping block with threshold state", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash(), "root", newHeadBlock.Root())
newHeadBlock = bc.GetBlock(newHeadBlock.ParentHash(), newHeadBlock.NumberU64()-1) // Keep rewinding
}
}
var newHeadBlock *types.Header
newHeadBlock, rootNumber = bc.rewindHead(header, root)
rawdb.WriteHeadBlockHash(db, newHeadBlock.Hash())

// Degrade the chain markers if they are explicitly reverted.
// In theory we should update all in-memory markers in the
// last step, however the direction of SetHead is from high
// to low, so it's safe to update in-memory markers directly.
bc.currentBlock.Store(newHeadBlock.Header())
headBlockGauge.Update(int64(newHeadBlock.NumberU64()))
bc.currentBlock.Store(newHeadBlock)
headBlockGauge.Update(int64(newHeadBlock.Number.Uint64()))

// The head state is missing, which is only possible in the path-based
// scheme. This situation occurs when the chain head is rewound below
// the pivot point. In this scenario, there is no possible recovery
// approach except for rerunning a snap sync. Do nothing here until the
// state syncer picks it up.
if !bc.HasState(newHeadBlock.Root()) {
log.Info("Chain is stateless, wait state sync", "number", newHeadBlock.Number(), "hash", newHeadBlock.Hash())
if !bc.HasState(newHeadBlock.Root) {
if newHeadBlock.Number.Uint64() != 0 {
log.Crit("Chain is stateless at a non-genesis block")
}
log.Info("Chain is stateless, wait state sync", "number", newHeadBlock.Number, "hash", newHeadBlock.Hash())
}
}
// Rewind the snap block in a simpleton way to the target head
Expand All @@ -733,6 +860,7 @@ func (bc *BlockChain) setHeadBeyondRoot(head uint64, time uint64, root common.Ha
// intent afterwards is full block importing, delete the chain segment
// between the stateful-block and the sethead target.
var wipe bool
frozen, _ := bc.db.Ancients()
if headNumber+1 < frozen {
wipe = pivot == nil || headNumber >= *pivot
}
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