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Previously, we knew the current slot and were able to tell that a block was from the future by comparing the block's slot against the current slot. For such blocks we would schedule a chain selection at the block's slot, which would be performed by a background thread. Now, we no longer know the current slot. Instead, we validate candidate chains and use the resulting ledgers to call `CheckInFuture`, which returns the headers in the candidate fragment that are from the future. We truncate these headers from the fragment, record that they're from the future (`cdbFutureBlocks`), and repeat chain selection without them. Headers that are too far into the future, i.e., exceeding the max clock skew, are not recorded in `cdbFutureBlocks`, but are recorded as invalid blocks (with `InFutureExceedsClockSkew` as the `InvalidBlockReason`). For each new block we receive, we perform chain selection for all future blocks before performing chain selection for the new block. * Rename `CandidateSuffix` to `ChainDiff`, split it off into a separate module, and use it throughout chain selection instead of only partially. A `ChainDiff` is the number of headers to roll back the current chain + a fragment containing the new headers to add, i.e., a diff w.r.t. the current chain. Previously, we converted such a `ChainDiff` to a `ChainAndLedger`, i.e., a fragment starting from the immutable tip (typically containing >= k headers) + a ledger matching the tip. Now, we stick to the `ChainDiff` until the end, when we actually install the candidate as the new chain by applying the diff. Also introduce `ValidatedChainDiff` and use that instead of `ChainAndLedger` for the validated candidate. We still use `ChainAndLedger` for the current chain. * Simplify `trySwitchTo` because there is no concurrency thanks to the queue introduced in #1709. Remove the obsolete trace message `ChainChangedInBg`. * New trace messages: - `ChainSelectionForFutureBlock` - `CandidateContainsFutureBlocks` - `CandidateContainsFutureBlocksExceedingClockSkew` * Remove `chainSelectionPerformed` from `AddBlockPromise` as it was not really used and complicated our new handling of blocks from the future. * Don't mark successors of an invalid block as invalid, as this is redundant, see why in `ChainDB.md`. This means we remove the `InChainAfterInvalidBlock` constructor of `InvalidBlockReason`. * Introduce `ChainSelEnv` to reduce the number of parameters to pass around.
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173 changes: 173 additions & 0 deletions
173
ouroboros-consensus/src/Ouroboros/Consensus/Fragment/Diff.hs
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| Original file line number | Diff line number | Diff line change |
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| {-# LANGUAGE FlexibleContexts #-} | ||
| {-# LANGUAGE PatternSynonyms #-} | ||
| {-# LANGUAGE StandaloneDeriving #-} | ||
| {-# LANGUAGE UndecidableInstances #-} | ||
| -- | Intended for qualified import | ||
| -- | ||
| -- > import Ouroboros.Consensus.Fragment.Diff (ChainDiff (..)) | ||
| -- > import qualified Ouroboros.Consensus.Fragment.Diff as Diff | ||
| module Ouroboros.Consensus.Fragment.Diff | ||
| ( ChainDiff(ChainDiff) | ||
| -- * Queries | ||
| , getRollback | ||
| , getSuffix | ||
| , getTip | ||
| , getAnchorPoint | ||
| -- * Constructors | ||
| , extend | ||
| , diff | ||
| -- * Application | ||
| , apply | ||
| -- * Manipulation | ||
| , truncate | ||
| , takeWhileOldest | ||
| ) where | ||
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| import Prelude hiding (truncate) | ||
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| import Data.Word (Word64) | ||
| import GHC.Stack (HasCallStack) | ||
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| import Ouroboros.Network.AnchoredFragment (AnchoredFragment (..)) | ||
| import qualified Ouroboros.Network.AnchoredFragment as AF | ||
| import Ouroboros.Network.Block (HasHeader, Point, castPoint) | ||
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| import Ouroboros.Consensus.Block (Header) | ||
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| -- | A diff of a chain (fragment). | ||
| -- | ||
| -- INVARIANT: the length of the suffix must always be >= the rollback | ||
| -- | ||
| -- Note: we allow the suffix with new headers to be empty, even though it is | ||
| -- rather pointless. Allowing empty ones makes working with them easier: fewer | ||
| -- cases to deal with. Without any headers, the rollback must be 0, so such a | ||
| -- diff would be an empty diff. | ||
| data ChainDiff blk = UnsafeChainDiff | ||
| { getRollback :: !Word64 | ||
| -- ^ The number of headers to roll back the current chain | ||
| , getSuffix :: !(AnchoredFragment (Header blk)) | ||
| -- ^ The new headers to add after rolling back the current chain. | ||
| } | ||
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| deriving instance (HasHeader blk, Eq (Header blk)) | ||
| => Eq (ChainDiff blk) | ||
| deriving instance (HasHeader blk, Show (Header blk)) | ||
| => Show (ChainDiff blk) | ||
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| -- | Allow for pattern matching on a 'ChainDiff' without exposing the (unsafe) | ||
| -- constructor. Use 'extend' and 'diff' to construct a 'ChainDiff'. | ||
| pattern ChainDiff | ||
| :: Word64 -> AnchoredFragment (Header blk) -> ChainDiff blk | ||
| pattern ChainDiff r s <- UnsafeChainDiff r s | ||
| {-# COMPLETE ChainDiff #-} | ||
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| -- | Internal. Return 'Nothing' if the length of the suffix < the rollback. | ||
| mkRollback | ||
| :: HasHeader (Header blk) | ||
| => Word64 | ||
| -> AnchoredFragment (Header blk) | ||
| -> Maybe (ChainDiff blk) | ||
| mkRollback nbRollback suffix | ||
| | fromIntegral (AF.length suffix) >= nbRollback | ||
| = Just $ UnsafeChainDiff nbRollback suffix | ||
| | otherwise | ||
| = Nothing | ||
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| {------------------------------------------------------------------------------- | ||
| Queries | ||
| -------------------------------------------------------------------------------} | ||
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| -- | Return the tip of the new suffix | ||
| getTip :: HasHeader (Header blk) => ChainDiff blk -> Point blk | ||
| getTip = castPoint . AF.headPoint . getSuffix | ||
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| -- | Return the anchor point of the new suffix | ||
| getAnchorPoint :: ChainDiff blk -> Point blk | ||
| getAnchorPoint = castPoint . AF.anchorPoint . getSuffix | ||
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| {------------------------------------------------------------------------------- | ||
| Constructors | ||
| -------------------------------------------------------------------------------} | ||
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| -- | Make an extension-only (no rollback) 'ChainDiff'. | ||
| extend :: AnchoredFragment (Header blk) -> ChainDiff blk | ||
| extend = UnsafeChainDiff 0 | ||
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| -- | Diff a candidate chain with the current chain. | ||
| -- | ||
| -- If the candidate fragment is shorter than the current chain, 'Nothing' is | ||
| -- returned (this would violate the invariant of 'ChainDiff'). | ||
| -- | ||
| -- PRECONDITION: the candidate fragment must intersect with the current chain | ||
| -- fragment. | ||
| diff | ||
| :: (HasHeader (Header blk), HasCallStack) | ||
| => AnchoredFragment (Header blk) -- ^ Current chain | ||
| -> AnchoredFragment (Header blk) -- ^ Candidate chain | ||
| -> Maybe (ChainDiff blk) | ||
| diff curChain candChain = | ||
| case AF.intersect curChain candChain of | ||
| Just (_curChainPrefix, _candPrefix, curChainSuffix, candSuffix) | ||
| -> mkRollback | ||
| (fromIntegral (AF.length curChainSuffix)) | ||
| candSuffix | ||
| -- Precondition violated. | ||
| _ -> error "candidate fragment doesn't intersect with current chain" | ||
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| {------------------------------------------------------------------------------- | ||
| Application | ||
| -------------------------------------------------------------------------------} | ||
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| -- | Apply the 'ChainDiff' on the given chain fragment. | ||
| -- | ||
| -- The fragment is first rolled back a number of blocks before appending the | ||
| -- new suffix. | ||
| -- | ||
| -- If the 'ChainDiff' doesn't fit (anchor point mismatch), 'Nothing' is | ||
| -- returned. | ||
| -- | ||
| -- The returned fragment will have the same anchor point as the given | ||
| -- fragment. | ||
| apply | ||
| :: HasHeader (Header blk) | ||
| => AnchoredFragment (Header blk) | ||
| -> ChainDiff blk | ||
| -> Maybe (AnchoredFragment (Header blk)) | ||
| apply curChain (ChainDiff nbRollback suffix) = | ||
| AF.join (AF.dropNewest (fromIntegral nbRollback) curChain) suffix | ||
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| {------------------------------------------------------------------------------- | ||
| Manipulation | ||
| -------------------------------------------------------------------------------} | ||
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| -- | Truncate the diff by rolling back the new suffix to the given point. | ||
| -- | ||
| -- PRECONDITION: the given point must correspond to one of the new headers of | ||
| -- the new suffix or its anchor (i.e, @'AF.withinFragmentBounds' pt (getSuffix | ||
| -- diff)@). | ||
| -- | ||
| -- If the length of the truncated suffix is shorter than the rollback, | ||
| -- 'Nothing' is returned. | ||
| truncate | ||
| :: (HasHeader (Header blk), HasCallStack, HasHeader blk) | ||
| => Point blk | ||
| -> ChainDiff blk | ||
| -> Maybe (ChainDiff blk) | ||
| truncate pt (ChainDiff nbRollback suffix) | ||
| | Just suffix' <- AF.rollback (castPoint pt) suffix | ||
| = mkRollback nbRollback suffix' | ||
| | otherwise | ||
| = error $ "rollback point not on the candidate suffix: " <> show pt | ||
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| -- | Return the longest prefix of the suffix matching the given predicate, | ||
| -- starting from the left, i.e., the \"oldest\" blocks. | ||
| -- | ||
| -- If the new suffix is shorter than the diff's rollback, return 'Nothing'. | ||
| takeWhileOldest | ||
| :: HasHeader (Header blk) | ||
| => (Header blk -> Bool) | ||
| -> ChainDiff blk | ||
| -> Maybe (ChainDiff blk) | ||
| takeWhileOldest accept (ChainDiff nbRollback suffix) = | ||
| mkRollback nbRollback (AF.takeWhileOldest accept suffix) |
69 changes: 69 additions & 0 deletions
69
ouroboros-consensus/src/Ouroboros/Consensus/Fragment/ValidatedDiff.hs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,69 @@ | ||
| {-# LANGUAGE PatternSynonyms #-} | ||
| -- | Intended for qualified import | ||
| -- | ||
| -- > import Ouroboros.Consensus.Fragment.ValidatedDiff (ValidatedChainDiff (..)) | ||
| -- > import qualified Ouroboros.Consensus.Fragment.ValidatedDiff as ValidatedDiff | ||
| module Ouroboros.Consensus.Fragment.ValidatedDiff | ||
| ( ValidatedChainDiff(ValidatedChainDiff) | ||
| , getChainDiff | ||
| , getLedger | ||
| , new | ||
| , toValidatedFragment | ||
| ) where | ||
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| import Control.Monad.Except (throwError) | ||
| import GHC.Stack (HasCallStack) | ||
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| import Ouroboros.Consensus.Fragment.Diff | ||
| import Ouroboros.Consensus.Fragment.Validated (ValidatedFragment) | ||
| import qualified Ouroboros.Consensus.Fragment.Validated as VF | ||
| import Ouroboros.Consensus.Ledger.Abstract | ||
| import Ouroboros.Consensus.Util.Assert | ||
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| -- | A 'ChainDiff' along with the ledger state after validation. | ||
| -- | ||
| -- INVARIANT: | ||
| -- | ||
| -- > getTip chainDiff == ledgerTipPoint ledger | ||
| data ValidatedChainDiff blk l = UnsafeValidatedChainDiff | ||
| { getChainDiff :: ChainDiff blk | ||
| , getLedger :: l | ||
| } | ||
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| -- | Allow for pattern matching on a 'ValidatedChainDiff' without exposing the | ||
| -- (unsafe) constructor. Use 'new' to construct a 'ValidatedChainDiff'. | ||
| pattern ValidatedChainDiff | ||
| :: ChainDiff blk -> l -> ValidatedChainDiff blk l | ||
| pattern ValidatedChainDiff d l <- UnsafeValidatedChainDiff d l | ||
| {-# COMPLETE ValidatedChainDiff #-} | ||
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| -- | Create a 'ValidatedChainDiff'. | ||
| -- | ||
| -- PRECONDITION: | ||
| -- | ||
| -- > getTip chainDiff == ledgerTipPoint ledger | ||
| new | ||
| :: (ApplyBlock l blk, HasCallStack) | ||
| => ChainDiff blk | ||
| -> l | ||
| -> ValidatedChainDiff blk l | ||
| new chainDiff ledger = | ||
| assertWithMsg precondition $ | ||
| UnsafeValidatedChainDiff chainDiff ledger | ||
| where | ||
| chainDiffTip = getTip chainDiff | ||
| ledgerTip = ledgerTipPoint ledger | ||
| precondition | ||
| | chainDiffTip == ledgerTip | ||
| = return () | ||
| | otherwise | ||
| = throwError $ | ||
| "tip of ChainDiff doesn't match ledger: " <> | ||
| show chainDiffTip <> " /= " <> show ledgerTip | ||
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| toValidatedFragment | ||
| :: (ApplyBlock l blk, HasCallStack) | ||
| => ValidatedChainDiff blk l | ||
| -> ValidatedFragment blk l | ||
| toValidatedFragment (UnsafeValidatedChainDiff cs l) = | ||
| VF.new (getSuffix cs) l |
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