gaslimit for a block and other questions related to gas model

Question

i know what is a gas, gaslimit and gasprice, but still have confusion even after searching and reading through the Internet.

• There is a gaslimit per block, but why many blocks did not reach it? in other words, can a miner send a block to the network without reaching the gaslimit for the block?

• Assume the block gaslimit is 4 million and i sent a transaction with 4 million gaslimit. But when the miner executed it (used gas was 1 million). Can the miner add extra transactions to the block to fill the remaining 3 million or not. In another way, does a transaction with a big gaslimit (but uses a fraction of that gas) affects the miner of adding more transactions to the block?

• Each Opcode coast some value of gas. How Ethereum measure the cost of each EVM opcode? (any reference for explanation?).

Thanks

Answer 1

Q1 The block gas limit is an upper bound on the total cost of transactions that can be included in a block. Yes, the miner can and should send a solved block to the network, even if the gas cost is 0. Blocks are meant to arrive at a steady pace in any case. So "nothing happened during this period" is a valid solution.

Q2a The gas cost of a transaction is the total cost of executing the transaction. Not subject to guesswork. If the actual cost exceeds the supplied gas then the transaction fails with an out-of-gas exception. If there is surplus gas, it's returned to the sender.

Q2b Yes, a miner can and should include multiple transactions in a block. A block is a well-ordered set of transactions that were accepted by the network. It's a unit of disambiguation that clearly defines the accepted order of events. Have a look here for exact meaning of this: https://ethereum.stackexchange.com/questions/13887/is-consensus-necessary-for-ethereum

Q3 I can't say for sure (possibly someone can confirm) that this is an up-to-date list: https://docs.google.com/spreadsheets/d/1m89CVujrQe5LAFJ8-YAUCcNK950dUzMQPMJBxRtGCqs/edit#gid=0