Max gas in sponsor transaction

[0xaptosj]

e### Discord user ID

No response

Describe your question in detail.

Asked by one of our partners who wants to create a NFT collection and sponsor the mint tx.

When we use maxGasAmount like below

• What are the implications of using a transaction value above what's actually required? Is it just returned to the funding account?
• And so similarly, how would I go about determining the appropriate transaction size if it should be adjusted to a more accurate dynamic value?
• And then a more abstract followup, what would be a typical necessary amount of funds to hold in a sponsoring account for this kind of event? (sponsor all mints in a single collection, say there are 10k mints)

      const transaction = await aptosClient().transaction.build.simple({
        withFeePayer: true,
        sender: account.address,
        data: {
          function: `${import.meta.env.VITE_MODULE_ADDRESS}::launchpad::mint_nft`,
          functionArguments: [collection.collection_id, 1],
        },
        options: {
          maxGasAmount: 10_000,
        },
      });

What error, if any, are you getting?

No response

What have you tried or looked at? Or how can we reproduce the error?

No response

Which operating system are you using?

Windows

Which SDK or tool are you using? (if any)

TypeScript SDK

Describe your environment or tooling in detail

No response

[0xaptosj]

Okay, it might be easier if I try to answer the individual questions. Not sure if the answers will make sense as I have to guess what they mean with the less precise terms used.

What are the implications of using a transaction value above what's actually required? Is it just returned to the funding account?

This feels like a general gas question. Assuming by transaction value they mean gas budget, or more precisely, max_gas_amount, then correct, only the actual used amount will be deducted from the fee payer account.

And so similarly, how would I go about determining the appropriate transaction size if it should be adjusted to a more accurate dynamic value?

Again, assuming that by appropriate transaction size they mean max_gas_amount, then I'd say they are probably better served by transaction simulation, which can return the estimated gas cost of the transaction, which is fairly accurate most of the time. Add some headroom to that you are all set.

And then a more abstract followup, what would be a typical necessary amount of funds to hold in a sponsoring account for this kind of event? (sponsor all mints in a single collection, say there are 10k mints)

Not familiar with sponsored transactions, but based on this comment ("Sponsoring a transaction requires that the sponsoring account have enough funds to cover the max possible gas fee.") it seems like the minimum should be maximum_number_of_gas_units (the global limit) multiplied by gas_unit_price.

i guess an easy question is, if we don't specify maxGasAmount, tx simulation will calculate that for me and deduct what's needed, right? so we can just suggest people not setting maxGasAmount

Correct. That's the same as my answer to the second question