The EVM executes, and it charges gas

Graduate · enrolled learners

This lesson opens with GovernMental, 2016.

What happened

GovernMental was a Ponzi-style game that recorded every participant in growing lists stored on-chain, and paying out a round required looping over and clearing those entire lists. Each step of that loop cost gas, and the total gas for the operation rose as the lists grew, until it exceeded the maximum gas that could fit in a single block. At that point the payout transaction could no longer be included in any block at all, because no block had room for it, so roughly 1,100 ether sat in a contract that could not run its own payout logic. The ether was eventually recovered much later, after the network's block gas limit had risen enough to fit the operation, but for a long time the funds were stuck, not by theft and not by a broken key, but by a design that let the cost of a function grow without bound. The contract asked the machine to do more work than a block could ever pay for, and the machine, which charges gas for every step and caps the gas per block, simply could not run it.

The decision point

The EVM charges gas for every operation it performs, and the gas that can fit in a single block is capped, so a function whose cost grows without bound will eventually cost more than a block allows and become impossible to execute, trapping whatever depends on it. GovernMental is the case: an unbounded list that had to be looped over and cleared grew until the operation exceeded the block gas limit, so the payout could not be included in any block and about 1,100 ether was stuck until the network's limit later rose. This is the foundational EVM lesson beneath all the others: on-chain computation is not free and is not unlimited, so a builder must think about cost the way they think about correctness, because a correct function that is too expensive to run is as useless as an incorrect one, and a function whose cost can grow, an unbounded loop, an unbounded array, a list that anyone can add to, can cross the block limit and lock the contract. So the discipline is to treat gas as a hard, finite resource: bound every loop and every storage structure a function must traverse, never let the cost of a critical operation depend on a quantity that can grow indefinitely, and design so that the essential functions of a contract can always be run within a block. GovernMental is what the gas model does to a design that ignores it: it does not reject the contract at deployment; it lets the cost creep upward until, one day, the contract can no longer do the one thing it exists to do.

Orientation and Year One are open: anyone can read them without an account. From Year Two onward the lessons are for enrolled learners, because progress through the later years only means anything if it is tracked against a record.

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