Fix performance regression of `GetFilteredDelegationsAndRewardAccount…

…s` (#104)

# Description

Addition of deposits made `rewView` extremly expensive, because it now
iterates the full staking credentials Map. The proper way to do it is to
restrict the Map first and then do the conversion.

This will very likely fix the timeout issue in
CardanoSolutions/ogmios#313

ouroboros-consensus-cardano/changelog.d/20230523_155615_alexey.kuleshevich_fix_performance_GetFilteredDelegationsAndRewardAccounts.md

@@ -0,0 +1,23 @@
+<!--
+A new scriv changelog fragment.
+
+Uncomment the section that is right (remove the HTML comment wrapper).
+-->
+
+
+### Patch
+
+- Fix performance regression of `GetFilteredDelegationsAndRewardAccounts` query
+
+<!--
+### Non-Breaking
+
+- A bullet item for the Non-Breaking category.
+
+-->
+<!--
+### Breaking
+
+- A bullet item for the Breaking category.
+
+-->

ouroboros-consensus-cardano/src/shelley/Ouroboros/Consensus/Shelley/Ledger/Query.hs

@@ -44,7 +44,8 @@ import qualified Cardano.Ledger.Shelley.LedgerState as SL (RewardAccounts)
 import qualified Cardano.Ledger.Shelley.PParams as SL (emptyPPPUpdates)
 import qualified Cardano.Ledger.Shelley.RewardProvenance as SL
                      (RewardProvenance)
-import           Cardano.Ledger.UMap (View (..), domRestrictedView, rewView)
+import           Cardano.Ledger.UMap (UMap (..), rdReward, tripDelegation,
+                     tripReward)
 import           Codec.CBOR.Decoding (Decoder)
 import qualified Codec.CBOR.Decoding as CBOR
 import           Codec.CBOR.Encoding (Encoding)
@@ -589,10 +590,12 @@ getFilteredDelegationsAndRewardAccounts ::
 getFilteredDelegationsAndRewardAccounts ss creds =
     (filteredDelegations, filteredRwdAcnts)
   where
-    u = SL.dsUnified $ getDState ss
+    UMap umElems _ = SL.dsUnified $ getDState ss
+    umElemsRestricted = Map.restrictKeys umElems creds
 
-    filteredDelegations = domRestrictedView creds $ Delegations u
-    filteredRwdAcnts = rewView u `Map.restrictKeys` creds
+    filteredDelegations = Map.mapMaybe tripDelegation umElemsRestricted
+    filteredRwdAcnts =
+      Map.mapMaybe (\e -> fromCompact . rdReward <$> tripReward e) umElemsRestricted
 
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