Tune gas per tx restrictions based on testnet feedback

[iramiller]

Summary

Based on initial testing of the 3M gas cap on transactions there have been significant concerns that certain atomic transactions will need to be broken apart which is undesirable. Despite the risks of allowing larger transactions an increase in this limit is desired.

Problem Definition

Certain critical transactions are very close to the 3M gas cap. In order to provide more flexibility and to ensure seamless support on mainnet the cap should be lifted from 3M to 4M. This adjustment will provide additional headroom and ensure that critical operations are not blocked on mainnet with the 1.8.0 upgrade. This is especially important as the limit is a compiled code change that would require another software upgrade to modify.

Proposal

• Decrease the minimum number of transactions per block from 20 to 15 (from 3M to 4M gas maximum)
• Move the rejection check higher in the antehandler flow so requests that exceed this cap are rejected sooner.

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