🎁 [Feature Request]: Consider making `total_supply` tracking optional

[dmkozh]

What is the feature you would like to see?

SEP-41 doesn't require tokens to implement supply tracking, so it's not required for the compliant tokens. Supply tracking has non-trivial performance cost, as its modification introduces a data dependency for all the transactions that use the token, which in turn makes them non-parallelizable, which reduces the token scalability.
It's hard to predict the exact impact - it depends on how often the token is being minted. But given the existence of the cost it would make sense to let the developer decide if they need this functionality given the potential performance cost.

[brozorec]

Thanks for raising this question @dmkozh 🙏

Indeed, SEP-41 doesn't require supply tracking for the reasons you mention, but they are specifically relevant for classic assets and their SACs. Custom tokens, which require more flexibility and because of that, won't be tied to a classic asset, can be SEP-41 compliant and "enjoy" additional functions.
Our goal by exposing a dedicated FungibleToken interface isn't to re-create/copy what's already available under soroban_sdk::token::TokenInterface but to give users more options for a "base" interface. Btw, FungibleToken is lacking burn and burn_from that must be implemented with FungibleBurnable for SEP-41 compliance.
We are providing examples for both approaches when creating SEP-41 compliant tokens, explaining transparently the trade-offs.

[dmkozh]

Custom tokens, which require more flexibility and because of that, won't be tied to a classic asset, can be SEP-41 compliant and "enjoy" additional functions.

Sure, my issue here is rather that if a custom token doesn't need supply tracking, it's better off not supporting it, as it's not completely free. My point re SEP-41 was just to make it clear that it can be optional.

[leighmcculloch]

The total supply field could be moved into an extension? FungibleTotalSupply

its modification introduces a data dependency for all the transactions that use the token

Only transactions that mint and burn would need to write to the shared storage. So on the surface the impact depends on how, and how frequently, the token will be minted. Because tokens are a building block total supply has some risk of serialising txs that might otherwise have been independent and making parallel execution less effective.