avoid re-writing code (#2490)

Avoids pointless rocksdb writes that cause write compaction /
amplification, specially in the case where code is shared between
multiple accounts

nimbus/db/ledger/backend/accounts_ledger.nim

@@ -347,12 +347,16 @@ proc persistMode(acc: AccountRef): PersistMode =
       result = Remove
 
 proc persistCode(acc: AccountRef, ac: AccountsLedgerRef) =
-  if acc.code.len != 0:
+  if acc.code.len != 0 and not acc.code.persisted:
     let rc = ac.kvt.put(
       contractHashKey(acc.statement.codeHash).toOpenArray, acc.code.bytes())
     if rc.isErr:
       warn logTxt "persistCode()",
        codeHash=acc.statement.codeHash, error=($$rc.error)
+    else:
+      # If the ledger changes rolled back entirely from the database, the ledger
+      # code cache must also be cleared!
+      acc.code.persisted = true
 
 proc persistStorage(acc: AccountRef, ac: AccountsLedgerRef) =
   const info = "persistStorage(): "
@@ -452,7 +456,7 @@ proc getCode*(ac: AccountsLedgerRef, address: EthAddress): CodeBytesRef =
             warn logTxt "getCode()", codeHash=acc.statement.codeHash, error=($$rc.error)
             CodeBytesRef()
           else:
-            let newCode = CodeBytesRef.init(move(rc.value))
+            let newCode = CodeBytesRef.init(move(rc.value), persisted = true)
             ac.code.lruAppend(acc.statement.codeHash, newCode, codeLruSize)
       else:
         CodeBytesRef()

nimbus/evm/code_bytes.nim

@@ -16,16 +16,21 @@ type CodeBytesRef* = ref object
   bytes: seq[byte]
   invalidPositions: seq[byte] # bit seq of invalid jump positions
   processed: int
+  persisted*: bool ## This code stream has been persisted to the database
 
 template bitpos(pos: int): (int, byte) =
   (pos shr 3, 1'u8 shl (pos and 0x07))
 
-func init*(T: type CodeBytesRef, bytes: sink seq[byte]): CodeBytesRef =
+func init*(
+    T: type CodeBytesRef, bytes: sink seq[byte], persisted = false
+): CodeBytesRef =
   let ip = newSeq[byte]((bytes.len + 7) div 8)
-  CodeBytesRef(bytes: move(bytes), invalidPositions: ip)
+  CodeBytesRef(bytes: move(bytes), invalidPositions: ip, persisted: persisted)
 
-func init*(T: type CodeBytesRef, bytes: openArray[byte]): CodeBytesRef =
-  CodeBytesRef.init(@bytes)
+func init*(
+    T: type CodeBytesRef, bytes: openArray[byte], persisted = false
+): CodeBytesRef =
+  CodeBytesRef.init(@bytes, persisted = persisted)
 
 func init*(T: type CodeBytesRef, bytes: openArray[char]): CodeBytesRef =
   CodeBytesRef.init(bytes.toOpenArrayByte(0, bytes.high()))