Gross gas cost is not enough and how to calculate the offset?

[Arisawa-v]

hello I’m measuring gas with debug_traceCall. My contract returns abi.encode(gasleft()). With a very high gas limit I get:

Gross Gas Cost (start − final gasleft()): ~2.46M

Net Gas Cost (trace.gasUsed, due to refunds): ~2.28M

But the tx only succeeds with at least 2.51M gas; setting the limit to ~gross OOGs. Calldata is short.

Is this extra ~0.05M the EIP-150 63/64 forwarding buffer for an early heavy subcall? What’s the correct way to compute the minimal non-OOG gas from a trace?

[mattsse]

estimating gas is tricky, this is pretty much tx specific, I assume estimagegas is not an option here?
one thing you could try is doing estimation on chain or work with additional buffers

[Arisawa-v]

thanks! but I want to confirm: is the gap between gross and non-OOG gas due to the EIP-150 63/64 rule? is the gap between gross and net gas due to refunds?

[Arisawa-v]

My use-case, is to measure the required gas at different transaction positions within a block. For that I need debug_traceCall’s TraceCallConfig.txIndex, which lets me run the call against the post-state after txIndex prior txs in the same block. I don’t see an equivalent txIndex control on eth_estimateGas, so I’m using debug_traceCall for this experiment.