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();
  });
});

Answer 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.

Answer 2

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.