perf: use module cache output from readFrom

All of our time was being spent reading modules from the database,
because the new readFrom didn't persist its cache back to the database
state. I think originally the reason why it didn't was to avoid
state leakage, but this is safe because the module cache is guaranteed
correct (it just does JSON parsing).

Change-Id: I405069a2ee17cfb4581df20402ff66c39675d90b

changes/2024-06-19T182645-0400.txt

@@ -0,0 +1,2 @@
+Fix a performance bug in read-only replay which was not using a cache
+for module data

src/Chainweb/Pact/Backend/RelationalCheckpointer.hs

@@ -153,11 +153,11 @@ doReadFrom logger v cid sql moduleCacheVar maybeParent doRead = do
         Nothing -> genesisHeight v cid
         Just parent -> succ . _blockHeight . _parentHeader $ parent
 
-  withMVar moduleCacheVar $ \sharedModuleCache -> do
+  modifyMVar moduleCacheVar $ \sharedModuleCache -> do
     bracket
       (beginSavepoint sql BatchSavepoint)
       (\_ -> abortSavepoint sql BatchSavepoint) $ \() -> do
-        getEndTxId "doReadFrom" sql maybeParent >>= traverse \startTxId -> do
+        h <- getEndTxId "doReadFrom" sql maybeParent >>= traverse \startTxId -> do
           newDbEnv <- newMVar $ BlockEnv
             (mkBlockHandlerEnv v cid currentHeight sql DoNotPersistIntraBlockWrites logger)
             (initBlockState defaultModuleCacheLimit startTxId)
@@ -184,7 +184,12 @@ doReadFrom logger v cid sql moduleCacheVar maybeParent doRead = do
               , _cpLookupProcessedTx = \hs ->
                 runBlockEnv newDbEnv (doLookupSuccessful currentHeight hs)
               }
-          doRead curBlockDbEnv
+          r <- doRead curBlockDbEnv
+          finalCache <- _bsModuleCache . _benvBlockState <$> readMVar newDbEnv
+          return (r, finalCache)
+        case h of
+          NoHistory -> return (sharedModuleCache, NoHistory)
+          Historical (r, finalCache) -> return (finalCache, Historical r)