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ChainDB: new approach to future blocks
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 from the future, i.e., exceeding the max clock skew, 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. * Split off `CandidateSuffix` into a separate module and use it throughout chain selection instead of only partially. A `CandidateSuffix` is the number of headers to roll back the current chain + a fragment containing the new headers to add, like a diff w.r.t. the current chain. Previously, we converted such a `CandidateSuffix` 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 `CandidateSuffix` until the end, when we actually install the candidate as the new chain by applying the diff. Also introduce `CandidateSuffixAndLedger` 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.
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ouroboros-consensus/src/Ouroboros/Consensus/Storage/ChainDB/Impl/CandidateSuffix.hs
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| {-# LANGUAGE FlexibleContexts #-} | ||
| {-# LANGUAGE PatternSynonyms #-} | ||
| {-# LANGUAGE StandaloneDeriving #-} | ||
| {-# LANGUAGE UndecidableInstances #-} | ||
| -- | Intended for qualified import | ||
| -- | ||
| -- > import Ouroboros.Consensus.Storage.ChainDB.Impl.CandidateSuffix | ||
| -- (CandidateSuffix (..), CandidateSuffixAndLedger) | ||
| -- > import qualified Ouroboros.Consensus.Storage.ChainDB.Impl.CandidateSuffix as CS | ||
| module Ouroboros.Consensus.Storage.ChainDB.Impl.CandidateSuffix | ||
| ( CandidateSuffix(CandidateSuffix) | ||
| , getRollback | ||
| , getSuffix | ||
| , getTip | ||
| , getAnchorPoint | ||
| , mkExtension | ||
| , mkRollback | ||
| , fitOn | ||
| , rollback | ||
| , intersect | ||
| , truncate | ||
| -- * With Ledger | ||
| , CandidateSuffixAndLedger | ||
| , getCandidateSuffix | ||
| , getLedger | ||
| , mkCandidateSuffixAndLedger | ||
| , toValidatedFragment | ||
| ) where | ||
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| import Prelude hiding (truncate) | ||
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| import Control.Monad.Except (throwError) | ||
| 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, HeaderHash, Point, | ||
| blockHash, castPoint) | ||
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| import Ouroboros.Consensus.Block (Header) | ||
| import Ouroboros.Consensus.Fragment.Validated (ValidatedFragment) | ||
| import qualified Ouroboros.Consensus.Fragment.Validated as VF | ||
| import Ouroboros.Consensus.Ledger.Abstract (ledgerTipPoint) | ||
| import Ouroboros.Consensus.Ledger.SupportsProtocol | ||
| (LedgerSupportsProtocol) | ||
| import Ouroboros.Consensus.Util.Assert | ||
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| import qualified Ouroboros.Consensus.Storage.ChainDB.Impl.LgrDB as LgrDB | ||
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| -- | Auxiliary data type for 'cdbAddBlock' for a candidate suffix. | ||
| -- | ||
| -- INVARIANT: the length of the suffix must always be >= the rollback | ||
| -- | ||
| -- Note: we allow the suffix to be empty, even though it is rather pointless. | ||
| -- Allowing empty ones makes working with them easier: fewer cases to deal | ||
| -- with. Such candidates will be filtered out at the end using | ||
| -- 'preferAnchoredCandidate' anyway. | ||
| data CandidateSuffix blk = UnsafeCandidateSuffix | ||
| { 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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||
| pattern CandidateSuffix | ||
| :: Word64 -> AnchoredFragment (Header blk) -> CandidateSuffix blk | ||
| pattern CandidateSuffix r s <- UnsafeCandidateSuffix r s | ||
| {-# COMPLETE CandidateSuffix #-} | ||
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| deriving instance (HasHeader blk, Eq (Header blk)) | ||
| => Eq (CandidateSuffix blk) | ||
| deriving instance (HasHeader blk, Show (Header blk)) | ||
| => Show (CandidateSuffix blk) | ||
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| -- | Return the tip of the suffix | ||
| getTip :: HasHeader (Header blk) => CandidateSuffix blk -> Point blk | ||
| getTip = castPoint . AF.headPoint . getSuffix | ||
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| -- | Return the anchor point of the suffix | ||
| getAnchorPoint :: CandidateSuffix blk -> Point blk | ||
| getAnchorPoint = castPoint . AF.anchorPoint . getSuffix | ||
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| -- | Make an extension-only (no rollback) 'CandidateSuffix'. | ||
| mkExtension :: AnchoredFragment (Header blk) -> CandidateSuffix blk | ||
| mkExtension = UnsafeCandidateSuffix 0 | ||
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| -- | Return 'Nothing' if the length of the suffix < the rollback | ||
| mkRollback | ||
| :: HasHeader (Header blk) | ||
| => Word64 | ||
| -> AnchoredFragment (Header blk) | ||
| -> Maybe (CandidateSuffix blk) | ||
| mkRollback nbRollback suffix | ||
| | fromIntegral (AF.length suffix) >= nbRollback | ||
| = Just $ UnsafeCandidateSuffix nbRollback suffix | ||
| | otherwise | ||
| = Nothing | ||
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| -- | Fit the candidate suffix on a chain after first rolling back the given | ||
| -- chain. | ||
| -- | ||
| -- If the given chain is the current chain on which the candidate is based, a | ||
| -- 'Just' will be returned. The returned candidate fragment will have the same | ||
| -- anchor point as the given chain. | ||
| fitOn | ||
| :: HasHeader (Header blk) | ||
| => AnchoredFragment (Header blk) | ||
| -> CandidateSuffix blk | ||
| -> Maybe (AnchoredFragment (Header blk)) | ||
| fitOn curChain (CandidateSuffix nbRollback suffix) = | ||
| AF.join (AF.dropNewest (fromIntegral nbRollback) curChain) suffix | ||
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| -- | Roll back the candidate suffix to the given point. | ||
| -- | ||
| -- PRECONDITION: the given point must correspond to one of the new headers of | ||
| -- the candidate suffix ('csSuffix') or the anchor of 'csRollback' (i.e, | ||
| -- @'AF.withinFragmentBounds' pt csSuffix@). | ||
| -- | ||
| -- If the length of the suffix rolled back to the given point is shorter than | ||
| -- the rollback ('csRollback'), 'Nothing' is returned. | ||
| rollback | ||
| :: (HasHeader (Header blk), HasCallStack, HasHeader blk) | ||
| => Point blk | ||
| -> CandidateSuffix blk | ||
| -> Maybe (CandidateSuffix blk) | ||
| rollback pt (CandidateSuffix 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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| -- | Calculate the candidate suffix of a fork of the current chain. | ||
| -- | ||
| -- If the candidate fragment is shorter than the current chain, 'Nothing' is | ||
| -- returned (this would violate the invariant of 'CandidateSuffix'). | ||
| -- | ||
| -- PRECONDITION: the candidate fragment must intersect with the current chain | ||
| -- fragment. | ||
| intersect | ||
| :: (HasHeader (Header blk), HasCallStack) | ||
| => AnchoredFragment (Header blk) -- ^ Current chain | ||
| -> AnchoredFragment (Header blk) -- ^ Candidate chain | ||
| -> Maybe (CandidateSuffix blk) -- ^ Candidate suffix | ||
| intersect 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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| -- | Truncate any blocks matching the given predicate in the candidate suffix. | ||
| -- | ||
| -- If the suffix becomes too short, return 'Nothing'. | ||
| truncate | ||
| :: HasHeader (Header blk) | ||
| => (HeaderHash blk -> Bool) -- ^ Truncate when 'True' | ||
| -> CandidateSuffix blk | ||
| -> Maybe (CandidateSuffix blk) | ||
| truncate reject (CandidateSuffix nbRollback suffix) = | ||
| mkRollback nbRollback (AF.takeWhileOldest (not . reject . blockHash) suffix) | ||
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| {------------------------------------------------------------------------------- | ||
| With Ledger | ||
| -------------------------------------------------------------------------------} | ||
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| -- | A 'CandidateSuffix' along with the ledger state after validation. | ||
| -- | ||
| -- INVARIANT: | ||
| -- | ||
| -- > getTip candidateSuffix == ledgerTipPoint (LgrDB.ledgerDbCurrent ledger) | ||
| data CandidateSuffixAndLedger blk = UnsafeCandidateSuffixAndLedger | ||
| { getCandidateSuffix :: CandidateSuffix blk | ||
| , getLedger :: LgrDB.LedgerDB blk | ||
| } | ||
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| -- | Create a 'CandidateSuffixAndLedger'. | ||
| -- | ||
| -- PRECONDITION: | ||
| -- | ||
| -- > getTip candidateSuffix == ledgerTipPoint (LgrDB.ledgerDbCurrent ledger) | ||
| mkCandidateSuffixAndLedger | ||
| :: (LedgerSupportsProtocol blk, HasCallStack) | ||
| => CandidateSuffix blk | ||
| -> LgrDB.LedgerDB blk | ||
| -> CandidateSuffixAndLedger blk | ||
| mkCandidateSuffixAndLedger candidateSuffix ledger = | ||
| assertWithMsg precondition $ | ||
| UnsafeCandidateSuffixAndLedger candidateSuffix ledger | ||
| where | ||
| suffixTip = getTip candidateSuffix | ||
| ledgerTip = ledgerTipPoint (LgrDB.ledgerDbCurrent ledger) | ||
| precondition | ||
| | suffixTip == ledgerTip | ||
| = return () | ||
| | otherwise | ||
| = throwError $ | ||
| "tip of candidateSuffix doesn't match ledger: " <> | ||
| show suffixTip <> " /= " <> show ledgerTip | ||
|
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| toValidatedFragment | ||
| :: (LedgerSupportsProtocol blk, HasCallStack) | ||
| => CandidateSuffixAndLedger blk | ||
| -> ValidatedFragment blk (LgrDB.LedgerDB blk) | ||
| toValidatedFragment (UnsafeCandidateSuffixAndLedger cs l) = | ||
| VF.new (getSuffix cs) l |
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