blockchaincontract-designcontract-developmentgo-ethereumweb3js
Hello it's been written many times, but as I observe none of the answers might be the one. I'm interested in the following thing. If in a smart contract I made the event , where will it be stored? in blockchain , if yes, where exactly?if not there, maybe in nodes? I'm building a serious app and i have to store many things there. so i have finally 2 questions.
1) where are logs stored exactly?
2)if in block header, can you describe how i can trust those logs getting in web3.js front-end?
these states are stored in the Contract's storage. Each contract has its own storage and memory space and both are in the blockchain(leveldb physically).
look at the diagram below to get an idea :
Strings can be stored in both Storage and Memory - it depends on the type of variable / usage - here's an example:
pragma solidity ^0.4.17;
contract StorageTest {
string string1; // string1 is storage
function func1(string param1) public pure { // param1 is memory
string memory string2 = "foo"; // string2 is memory in this instance
}
}
There's a great section in the Solidity documentation
And also a great answer from @eth about memory in Ethereum
Best Answer
You can trust the logs because they are stored in their respective block. If a log gets changed it would change the blockhash, receiptRoot, etc , same as with transactions. The merkle tree would not be the same anymore.
So if I execute a function at a certain block heights the receipt and thus the log will also be part of the block at that height as well as my transaction.
To answer where they are stored exactrly. In the transactions receipt trie if I recall correctly.
picture credit from https://medium.com/@preethikasireddy/how-does-ethereum-work-anyway-22d1df506369