Store most recent cert in the PerasCertDB

ouroboros-consensus/src/ouroboros-consensus/Ouroboros/Consensus/Storage/PerasCertDB/API.hs

@@ -35,6 +35,14 @@ data PerasCertDB m blk = PerasCertDB
   -- The 'Fingerprint' is updated every time a new certificate is added, but it
   -- stays the same when certificates are garbage-collected.
   , getCertSnapshot :: STM m (PerasCertSnapshot blk)
+  , getLatestCertSeen :: STM m (Maybe (WithArrivalTime (ValidatedPerasCert blk)))
+  -- ^ Get the certificate with the highest round number that has been added to
+  -- the db since it has been opened. This certificate is not affected by garbage
+  -- collection, but it's forgotten when the db is closed.
+  --
+  -- NOTE: having seen a certificate is a precondition to start voting in every
+  -- round except for the first one (at origin). As a consequence, only caught-up
+  -- nodes can actively participate in the Peras protocol for now.
   , garbageCollect :: SlotNo -> m ()
   -- ^ Garbage-collect state older than the given slot number.
   , closeDB :: m ()

ouroboros-consensus/src/ouroboros-consensus/Ouroboros/Consensus/Storage/PerasCertDB/Impl.hs

@@ -79,6 +79,7 @@ openDB args = do
       { addCert = getEnv1 h implAddCert
       , getWeightSnapshot = getEnvSTM h implGetWeightSnapshot
       , getCertSnapshot = getEnvSTM h implGetCertSnapshot
+      , getLatestCertSeen = getEnvSTM h implGetLatestCertSeen
       , garbageCollect = getEnv1 h implGarbageCollect
       , closeDB = implCloseDB h
       }
@@ -170,18 +171,22 @@ implAddCert env cert = do
     if Map.member roundNo pvcsCerts
       then pure PerasCertAlreadyInDB
       else do
+        let pvcsCerts' = Map.insert roundNo cert pvcsCerts
         let pvcsLastTicketNo' = succ pvcsLastTicketNo
         writeTVar pcdbVolatileState $
           WithFingerprint
             PerasVolatileCertState
               { pvcsCerts =
-                  Map.insert roundNo cert pvcsCerts
+                  pvcsCerts'
               , -- Note that the same block might be boosted by multiple points.
                 pvcsWeightByPoint =
                   addToPerasWeightSnapshot boostedPt (getPerasCertBoost cert) pvcsWeightByPoint
               , pvcsCertsByTicket =
                   Map.insert pvcsLastTicketNo' cert pvcsCertsByTicket
-              , pvcsLastTicketNo = pvcsLastTicketNo'
+              , pvcsLastTicketNo =
+                  pvcsLastTicketNo'
+              , pvcsLatestCertSeen =
+                  snd <$> Map.lookupMax pvcsCerts'
               }
             (succ fp)
         pure AddedPerasCertToDB
@@ -220,6 +225,14 @@ implGetCertSnapshot PerasCertDbEnv{pcdbVolatileState} =
               snd $ Map.split ticketNo pvcsCertsByTicket
           }
 
+implGetLatestCertSeen ::
+  IOLike m =>
+  PerasCertDbEnv m blk -> STM m (Maybe (WithArrivalTime (ValidatedPerasCert blk)))
+implGetLatestCertSeen PerasCertDbEnv{pcdbVolatileState} =
+  readTVar pcdbVolatileState
+    <&> forgetFingerprint
+    <&> pvcsLatestCertSeen
+
 implGarbageCollect ::
   forall m blk.
   IOLike m =>
@@ -236,12 +249,14 @@ implGarbageCollect PerasCertDbEnv{pcdbVolatileState} slot =
       , pvcsWeightByPoint
       , pvcsLastTicketNo
       , pvcsCertsByTicket
+      , pvcsLatestCertSeen
       } =
       PerasVolatileCertState
         { pvcsCerts = Map.filter keepCert pvcsCerts
         , pvcsWeightByPoint = prunePerasWeightSnapshot slot pvcsWeightByPoint
         , pvcsCertsByTicket = Map.filter keepCert pvcsCertsByTicket
         , pvcsLastTicketNo = pvcsLastTicketNo
+        , pvcsLatestCertSeen = pvcsLatestCertSeen
         }
      where
       keepCert cert =
@@ -269,6 +284,9 @@ data PerasVolatileCertState blk = PerasVolatileCertState
   , pvcsLastTicketNo :: !PerasCertTicketNo
   -- ^ The most recent 'PerasCertTicketNo' (or 'zeroPerasCertTicketNo'
   -- otherwise).
+  , pvcsLatestCertSeen :: !(Maybe (WithArrivalTime (ValidatedPerasCert blk)))
+  -- ^ The certificate with the highest round number that has been added to the
+  -- db since it has been opened.
   }
   deriving stock (Show, Generic)
   deriving anyclass NoThunks
@@ -281,6 +299,7 @@ initialPerasVolatileCertState =
       , pvcsWeightByPoint = emptyPerasWeightSnapshot
       , pvcsCertsByTicket = Map.empty
       , pvcsLastTicketNo = zeroPerasCertTicketNo
+      , pvcsLatestCertSeen = Nothing
       }
     (Fingerprint 0)
 
@@ -305,7 +324,6 @@ invariantForPerasVolatileCertState pvcs = do
           <> " > "
           <> show pvcsLastTicketNo
  where
-  PerasVolatileCertState _ _ _ _keep = forgetFingerprint pvcs
   PerasVolatileCertState
     { pvcsCerts
     , pvcsWeightByPoint

ouroboros-consensus/test/storage-test/Test/Ouroboros/Storage/PerasCertDB/Model.hs

@@ -11,6 +11,7 @@ module Test.Ouroboros.Storage.PerasCertDB.Model
   , closeDB
   , addCert
   , getWeightSnapshot
+  , getLatestCertSeen
   , garbageCollect
   , hasRoundNo
   ) where
@@ -19,35 +20,40 @@ import Data.Set (Set)
 import qualified Data.Set as Set
 import GHC.Generics (Generic)
 import Ouroboros.Consensus.Block
-import Ouroboros.Consensus.BlockchainTime.WallClock.Types (WithArrivalTime)
+import Ouroboros.Consensus.BlockchainTime.WallClock.Types (WithArrivalTime, forgetArrivalTime)
 import Ouroboros.Consensus.Peras.Weight
   ( PerasWeightSnapshot
   , mkPerasWeightSnapshot
   )
+import Ouroboros.Consensus.Util (safeMaximumOn)
 
 data Model blk = Model
   { certs :: Set (WithArrivalTime (ValidatedPerasCert blk))
+  , latestCertSeen :: Maybe (WithArrivalTime (ValidatedPerasCert blk))
   , open :: Bool
   }
   deriving Generic
 
 deriving instance StandardHash blk => Show (Model blk)
 
 initModel :: Model blk
-initModel = Model{open = False, certs = Set.empty}
+initModel = Model{open = False, certs = Set.empty, latestCertSeen = Nothing}
 
 openDB :: Model blk -> Model blk
 openDB model = model{open = True}
 
 closeDB :: Model blk -> Model blk
-closeDB _ = Model{open = False, certs = Set.empty}
+closeDB _ = Model{open = False, certs = Set.empty, latestCertSeen = Nothing}
 
 addCert ::
   StandardHash blk =>
   Model blk -> WithArrivalTime (ValidatedPerasCert blk) -> Model blk
 addCert model@Model{certs} cert
   | certs `hasRoundNo` cert = model
-  | otherwise = model{certs = Set.insert cert certs}
+  | otherwise = model{certs = certs', latestCertSeen = safeMaximumOn roundNo (Set.toList certs')}
+ where
+  certs' = Set.insert cert certs
+  roundNo = getPerasCertRound . forgetArrivalTime
 
 hasRoundNo ::
   Set (WithArrivalTime (ValidatedPerasCert blk)) ->
@@ -65,6 +71,11 @@ getWeightSnapshot Model{certs} =
     | cert <- Set.toList certs
     ]
 
+getLatestCertSeen ::
+  Model blk -> Maybe (WithArrivalTime (ValidatedPerasCert blk))
+getLatestCertSeen Model{latestCertSeen} =
+  latestCertSeen
+
 garbageCollect :: SlotNo -> Model blk -> Model blk
 garbageCollect slot model@Model{certs} =
   model{certs = Set.filter keepCert certs}

ouroboros-consensus/test/storage-test/Test/Ouroboros/Storage/PerasCertDB/StateMachine.hs

@@ -72,6 +72,7 @@ instance StateModel Model where
     CloseDB :: Action Model ()
     AddCert :: WithArrivalTime (ValidatedPerasCert TestBlock) -> Action Model AddPerasCertResult
     GetWeightSnapshot :: Action Model (PerasWeightSnapshot TestBlock)
+    GetLatestCertSeen :: Action Model (Maybe (WithArrivalTime (ValidatedPerasCert TestBlock)))
     GarbageCollect :: SlotNo -> Action Model ()
 
   arbitraryAction _ (Model model)
@@ -80,6 +81,7 @@ instance StateModel Model where
           [ (1, pure $ Some CloseDB)
           , (20, Some <$> genAddCert)
           , (20, pure $ Some GetWeightSnapshot)
+          , (10, pure $ Some GetLatestCertSeen)
           , (5, Some . GarbageCollect . SlotNo <$> arbitrary)
           ]
     | otherwise = pure $ Some OpenDB
@@ -128,6 +130,7 @@ instance StateModel Model where
     CloseDB -> Model.closeDB model
     AddCert cert -> Model.addCert model cert
     GetWeightSnapshot -> model
+    GetLatestCertSeen -> model
     GarbageCollect slot -> Model.garbageCollect slot model
 
   precondition (Model model) = \case
@@ -140,6 +143,7 @@ instance StateModel Model where
          where
           p cert' = getPerasCertRound cert /= getPerasCertRound cert' || cert == cert'
         GetWeightSnapshot -> True
+        GetLatestCertSeen -> True
         GarbageCollect _slot -> True
 
 deriving stock instance Show (Action Model a)
@@ -162,6 +166,9 @@ instance RunModel Model (StateT (PerasCertDB IO TestBlock) IO) where
     GetWeightSnapshot -> do
       perasCertDB <- get
       lift $ atomically $ forgetFingerprint <$> PerasCertDB.getWeightSnapshot perasCertDB
+    GetLatestCertSeen -> do
+      perasCertDB <- get
+      lift $ atomically $ PerasCertDB.getLatestCertSeen perasCertDB
     GarbageCollect slot -> do
       perasCertDB <- get
       lift $ PerasCertDB.garbageCollect perasCertDB slot
@@ -177,6 +184,11 @@ instance RunModel Model (StateT (PerasCertDB IO TestBlock) IO) where
     counterexamplePost $ "Model: " <> show expected
     counterexamplePost $ "SUT: " <> show actual
     pure $ expected == actual
+  postcondition (Model model, _) GetLatestCertSeen _ actual = do
+    let expected = Model.getLatestCertSeen model
+    counterexamplePost $ "Model: " <> show expected
+    counterexamplePost $ "SUT: " <> show actual
+    pure $ expected == actual
   postcondition _ _ _ _ = pure True
 
   monitoring (Model model, _) (AddCert cert) _ _ prop =