How accurate are Etherscan's internal tx's on Rinkeby for Oraclize calls?

Question

I'm trying to optimize my smart contract and am breaking down where the gas is being spent.

Each execution for one function costs me about $5 in gas. I looked at Etherscan and in the internal tx's it shows a value of $5 sent to Oraclize address for my Oraclize call (just a URL call).

Am i really sending that much gas to Oraclize or is Etherscan's value calculator for internal tx's including storage costs in the function that places the Oraclize call? My oraclize call I put 800000 for gas in the custom parameter.

Thanks for any clarification.

Answer 1

Disclosure: am an Oraclize employee.

 

There includes in the Oraclize API a helper function called oraclize_getPrice. It expects two parameters, the first is the data-source you are querying, for example "URL" or "computation", and the second is the gas limit you are providing to Oraclize to run your __callback. It returns the amount of Wei as a type 'uint' that your query will cost, and so take out of your contract when you call oraclize_query.

 

It's calculated by taking your gas limit supplied (in your case 800000) and multiplying it by the gas price you may or may not have specified. If you haven't set a custom limit via oraclize_setCustomGasPrice then it will default to 20gwei. It will then add to this the base price of the query type you are making, in this case "URL", plus any additional fee for a proof type (You can see the breakdown here). Fees are calculated in Wei using the current USD/ETH exchange rate.

 

Calculating just the gas cost of your fee (as you did in your reply):

 

800000 gasLimit * 20e8 gasPrice = 0.016 ETH

 

Which at the current ETH prices you can see is by far the larger part of the $5 (~ 90%) fee you're seeing leave you contract. And as such, it's imperative you make your __callback (and indeed any function in Solidity) as gas efficient as possible!

 

W/r/t pivoting away from Oraclize, that is of course your prerogative. You still ought to fine-tune the gas prices of your contract functions, since those will need to be paid regardless by either yourself or users of your smart-contract.

 

But what Oraclize offer as a service is a trustless model where, via the proof-types supplied, you don't have to trust Oraclize at all. Better still, you can put a value on that trustlessness. By choosing say the TLS_Notary proof, you're relying on an AWS instance, the cost of hacking/breaking/altering then is quantifiable. This means you know for how much your Oraclize-dependant contract is "safe", incentivally speaking.

 

You can absolutely roll your own of course, but should you start requiring this level of quantifiable trustlessness and thus start implementing the structures required to achieve this, you may soon start to appreciate that $0.05c fee after all!

Answer 2

The answer is that it is accurate for how much value you're sending to Oraclize and not just how much value was used in the function.

I looked at Oraclize docs. and they use gasPrice of 20 Gwei and I'm setting a custom gasLimit of 800000. Oraclize can't refund unused gas so they take it all.

So 20 Gwei * 800000 wei = 0.016 ETH. Solution would be change the gasPrice from 20 Gwei or gasLimit to lower or don't use Oraclize.