Why does deploying a contract causes two transactions?

Question

I am new to Ethereum, learning about smart contracts.
I have a simple hello world contract.

# @version ^0.3.7
@external
@pure
def hola() -> String[5]:
    return "hola!"

Currently, I'm doing experiments to find out how much wei it costs to deploy a contract.

When I deploy my contract to Ganache UI, its log shows two transactions, with two separate gas fees.

Question: I only expect one transaction. Why are there two?

Ganache Log:

[5:23:15 PM]   Transaction: 0x1fd75f313be224fb941c37d62548c0e68cba47ce61f99a2c5d2ff0db646418d2
[5:23:15 PM]   Contract created: 0x56f36098ae392a06540387ffa56ea43624e806e7
[5:23:15 PM]   Gas usage: 201627
[5:23:15 PM]   Block Number: 6
[5:23:15 PM]   Block Time: Tue Feb 07 2023 17:23:15 GMT+0700 (Indochina Time)
[5:23:15 PM] eth_getTransactionReceipt[5:23:15 PM] eth_getBlockByNumber
[5:23:15 PM] eth_getCode[5:23:15 PM] eth_getBlockByNumber
[5:23:15 PM] eth_getBlockByNumber[5:23:15 PM] eth_estimateGas
[5:23:15 PM] eth_getBlockByNumber[5:23:15 PM] eth_gasPrice
[5:23:15 PM] eth_sendTransaction
[5:23:15 PM]   Transaction: 0xeb19faa88d021e2e94e2a89a5718b64793e8e47936bff2dc9008bb22c298f297
[5:23:15 PM]   Gas usage: 42513
[5:23:15 PM]   Block Number: 7
[5:23:15 PM]   Block Time: Tue Feb 07 2023 17:23:15 GMT+0700 (Indochina Time)

Truffle config:

  networks: {
    development: {
      host: "127.0.0.1",
      port: 7545,
      network_id: "*",
    }

Test/Deploy code:

const Hello = artifacts.require("Hello");
contract("Hello Only", () => {
  it("...should deploy", async () => {
    const hello = await Hello.deployed();
  });
});

truffle deploy a migration contract, this must be excluded somehow when deployen to mainnet. check this https://ethereum.stackexchange.com/questions/8299/what-are-truffle-migrations — Majd TL, Feb 07 '23 at 12:48
that's why I stopped used truffle, when I discovered they store deployment info on the chain. what a horrible design idea — Nulik, Feb 07 '23 at 17:23
@Nulik I agree. After posting, I found several other Truffle questions and bug reports expressing the same bewilderment. I won't use Truffle again. — devdanke, Feb 08 '23 at 15:27
@devdanke the best way to deploy is to use scripts in golang. there is abigen command for that, it will create constructor with parameters and also wrapper for all the functions. I am compiling contracts with solc to produce combined json format and then just do: abigen --combined-json artifacts.json --pkg whatever ..etc.... — Nulik, Feb 09 '23 at 00:51
@Nulik I'm having success with the Web3j Ethereum client. It can be used in Java, Kotlin, Scala, and Clojure etc. It can also be used in Android apps. — devdanke, Feb 09 '23 at 14:04
@MajdTL Your comment answered my question :-) Please post your comment as an Answer. Then I will Accept it. Thank you. — devdanke, Feb 09 '23 at 14:13

score 1 · Accepted Answer · answered Feb 09 '23 at 15:57

1

Truffle deploys an extra migration contract. check this question What are truffle migrations? for more information about it.

This migration contract should be excluded somehow when deployen to mainnet or run the tests.

answered Feb 09 '23 at 15:57

Majd TL

3,217
3
17
36

score -1 · Answer 2 · answered Feb 07 '23 at 14:49

-1

The first one, with gas usage: 201627, is for the creation of the contract (deploying to the network). The fees after that is to run the contract on the network.

answered Feb 07 '23 at 14:49

JacquesVrolijk

44
3

No. The second transaction isn't to "run" the contract. Instead, (I learned from @Majd TL) the second transaction posts meta data about my contract to a Truffle migration history contract. As you can see in my test code above, after deployment, there is no other interaction with my contract. – devdanke Feb 08 '23 at 15:34

Why does deploying a contract causes two transactions?

2 Answers2