Transactions in BlockChain

[aviorn36]

Hi Community, as I am progressing with the course, I am getting some generic doubts for which your suggestion and guidance would be really helpful. Some part of question may be valid if an only my understandings are correct, my sincere apologies if they are not valid or if you find it absurd.

1. When multiple transactions are created, are all these transactions in some common memory for nodes to pick up or are those transactions copied to all the nodes? How would this fit into picture while deploying a smart contract as it is said that we deploy smart contracts via transaction (if I am correct) ?

2. Is this understanding correct? "A smart contract is said to be deployed to block chain, if the block containing smart contract transaction is added to the block chain after consensus".

3. Is this understanding correct? "When a block is added to the chain after consensus, all other nodes adds the same block to their respective chain. If that block contains any transaction which holds a smart contract, that smart contract is tagged with an address which we can use to communicate to. So this means all the nodes after copying that block is going to have a transaction which would have deployed same smart contract with the same address".

4. When some user initiates/creates transaction where-in they intend to use some functions of a smart contract present in block chain. When is that function actually triggered? Is it triggered after that transaction is collected in a block computed for nonce and added to block o what is the actual process?

5. It is said that block chain are generally deterministic system so any randomness like random number generator / api calls are not allowed from the block chain network. But still we would need to interact with real world external system for which we have de-centralised chainLink oracle which does all those task for block chain, but chainLink is itself Ethereum based block chain. Does this not contradict the very core principal of block chain being/should be deterministic?

[othaime-en]

Hey @aviorn36

1. Other than the main chain, nodes also keep a small memory pool (mempool) it sort of a small database containing unconfirmed transactions that need to be added to the blockchain. So if you trigger a transaction right now, your transaction first goes to the mempool then after it is confirmed, it is permanently stored in the blockchain. Concerning smart contract, it is all the same. All interactions with smart contracts (deploying and calling functions) are in the form of transactions. So even when you deploy a smart contract, it still goes to the mempool to be confirmed first before it is added to the blockchain.
2. Yes that is correct.
3. Technically yes. Once the block containing the contract is mined and added to the blockchain after several confirmations, all the nodes on the chain have a copy of this block which contains the deployed smart contract. It is important to note that there is a slight difference between normal transactions and transactions that deploy smart contracts. When smart contracts are deployed, they are automatically given a contract address that others can use to interact with it in future. So other than the deployment transaction being on the chain, we introduce another account/address that holds the smart contract. So if you want to call a function from the contract, you can call it through this address.
4. When you call a function from a smart contract, this interaction exists in the form of a transaction just like any other transaction. I think by now you know that all that the blockchain does is just record state changes right? so this interaction with the smart contract is also meant to trigger a state change in the blockchain. However, that change has to be confirmed first like every other normal transaction. So if the transaction gets rejected, the state remains as it was, but if it gets confirmed and added to the blockchain, then we can say the function was indeed triggered and the state of the blockchain changed to whatever the function was meant to achieve.
5. It is true that chainlink oracles are ethereum-based chains. However one distinct difference you need to note when it comes to determinism is that the ethereum mainnet is closed off to itself while the chainlink nodes interact with outside system which we use to generate randomness. So we generate randomness off-chain then we introduce it to the blockchain through blockchain oracles.

[krakxn]

Clarifying,

1: Clients (users) make a request (for their transaction) which the nodes recognize and if it is valid, stored in the mempool to prepare for the block. From this mempool, (the order precedence) txns which yield the most profits for the validator (Ethereum, for Bitcoin this auction is not present, however the mempool for preparing is) are selected for the block to be mined.

5: It is not a core principal; it instead is just not possible to generate randomness on-chain because blockchains are deterministic systems. Therefore, we look for off-chain solutions such as a decentralized oracle to generate randomness. There is no "breaking of the principal" here.

[aviorn36]

Thank you @othaime-en @krakxn. Hoping if some one can confirm/clarify on below comments.
4. So when a node mines a block and if it is successfully added to the chain, all the other nodes other than adding the mined block to their respective chain they also clears out all those transactions from their mempool which have been included in the block. I hope this is right to say and this property in inherently provided by the blockchain protocol in use.

6. Just a clarification, when I say implementing a way of randomness in chainLink oracles some how violates principal of deterministic system, I meant violation for ethereum based chainLink oracles (built on blockchain principals) and not for ethereum mainnet which is closed off to itself (as it is clearly not in any violation). Can you please shed some light here too?

[alymurtazamemon]

@aviorn36

4. Yes
5. Chainlink is not a blockchain, it is a blockchain oracle network that is decentralized.

**Blockchain Oracle:**These are the devices that interact with the off-chain world and do all the computation and provide data back to smart contracts.

The chainlink nodes that we talk about in the discussion and you must hear in a video are the blockchain oracles.

And could please clarify how you think It breaks the principal of deterministic systems?

[aviorn36]

@alymurtazamemon , i guess I somehow missed this chain. Apologies. Back to the query, when I was going through the course what I understood was Chainlink is itself EVM based block-chain, so naturally I thought Chainlink to be a block-chain architecture. Hence my query of it breaking deterministic principal. I hope this make sense.