WASM execution without prior deployment

[jakmeier]

A truly stateless validator would not have access to pre-deployed contract code.
If we can't rely on that optimization, how much slower would WASM execution be and what can we do about it?

Luckily, we have already spent a lot of time optimizing compilation and are proud of our linear in time and space complexity WASM validation & compilation passes. So maybe it's actually okay to add this extra latency?

According to our gas costs today, compilation takes ~0.3ms + ~6.4ms per 100kB on a chunk producer.

• For SWEAT (204kB) it would be ~13.356ms
• For SocialDB (392kB) it would be ~25.388ms
• For Aurora (1MB) it would be ~64.3ms

Adding this extra delay for every function call on the stateless validator is unfortunate. But something we can potentially overcome.

Also note that due to everything being in-memory on the stateless validator, all storage related costs should be much faster. So for storage access heavy receipts, chunks would be produced much slower than stateless validators can validate them if they are running on comparable CPUs.

Other possible solutions to get around the compilation include:

• Store x86 on-chain instead of WASM and include this in the witness. (downside: increases witness size)
• Interpret WASM instead of compiling it.

[robin-near]

Validators can locally cache compiled contracts. Hopefully this will resolve most cases?

[jakmeier]

Yeah that's right, for the foreseeable future even a stateless validator should have enough disk space to cache the executables. There will be an ugly drop in performance anytime we have a protocol upgrade that invalidates old compilation results.
But I would expect it to be fine anyway. Or at least I think we have bigger problems to worry about first. :P

[jakmeier]

near/NEPs#481 (comment) contains some info about interpreter speed if we ever want to go down that route anyway

[nagisa]

Just to add an alternative which is not written down: ZK validation does not care as much about execution time as there's only a single (or a couple) machines actually doing the actual execution and giving a significant time for the validators to compile and execute the contracts only serves to increase latency of individual transactions, rather than throughput of the network.