evm: code comments and cleanup (#404)

* evm: code comments and cleanup

* context comment

* abci, tx type event and metrics

* statedb comments

x/evm/types/events.go

@@ -8,6 +8,7 @@ const (
 	AttributeKeyRecipient       = "recipient"
 	AttributeKeyTxHash          = "txHash"
 	AttributeKeyEthereumTxHash  = "ethereumTxHash"
+	AttributeKeyTxType          = "txType"
 	// tx failed in eth vm execution
 	AttributeKeyEthereumTxFailed = "ethereumTxFailed"
 	AttributeValueCategory       = ModuleName

x/evm/types/key.go

@@ -30,9 +30,6 @@ const (
 	prefixLogs
 	prefixCode
 	prefixStorage
-	prefixChainConfig
-	prefixHashTxReceipt
-	prefixBlockHeightTxs
 )
 
 const (
@@ -53,9 +50,6 @@ var (
 	KeyPrefixLogs               = []byte{prefixLogs}
 	KeyPrefixCode               = []byte{prefixCode}
 	KeyPrefixStorage            = []byte{prefixStorage}
-	KeyPrefixChainConfig        = []byte{prefixChainConfig}
-	KeyPrefixHashTxReceipt      = []byte{prefixHashTxReceipt}
-	KeyPrefixBlockHeightTxs     = []byte{prefixBlockHeightTxs}
 )
 
 var (
@@ -85,17 +79,6 @@ func StateKey(address ethcmn.Address, key []byte) []byte {
 	return append(AddressStoragePrefix(address), key...)
 }
 
-// KeyHashTxReceipt returns a key for accessing tx receipt data by hash.
-func KeyHashTxReceipt(hash ethcmn.Hash) []byte {
-	return append(KeyPrefixHashTxReceipt, hash.Bytes()...)
-}
-
-// KeyBlockHeightTxs returns a key for accessing tx hash list by block height.
-func KeyBlockHeightTxs(height uint64) []byte {
-	heightBytes := sdk.Uint64ToBigEndian(height)
-	return append(KeyPrefixBlockHeightTxs, heightBytes...)
-}
-
 // KeyAddressStorage returns the key hash to access a given account state. The composite key
 // (address + hash) is hashed using Keccak256.
 func KeyAddressStorage(address ethcmn.Address, hash ethcmn.Hash) ethcmn.Hash {