code: func dbPutTxIndexEntry(dbTx database.Tx, txHash *chainhash.Hash, serializedData []byte) error {
  	txIndex := dbTx.Metadata().Bucket(txIndexKey)
  	return txIndex.Put(txHash[:], serializedData)
  }
docs: // dbPutTxIndexEntry uses an existing database transaction to update the
  // transaction index given the provided serialized data that is expected to have
  // been serialized putTxIndexEntry.