neo-cli: tune MaxTransactionsPerBlock for testnet

[roman-khimov]

Allow to flush the mempool in just 10 blocks.

[Jim8y]

Do we have an approximate maximum execution time of a single transction, just in case of Resource Exhaustion Attack?

[roman-khimov]

It's strongly correlated with GAS cost and we have MaxBlockSystemFee limit (somewhat optimistic I'd say, but still). We also know that C# node can handle several thousands of NEO transfers per second, so with 15s block time 5K doesn't seem to be a lot of transactions.

[coveralls]

Pull Request Test Coverage Report for Build 1803322398

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 14.936%

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Totals
Change from base Build 1582407624:	0.0%
Covered Lines:	107
Relevant Lines:	694

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💛 - Coveralls

[Jim8y]

@roman-khimov I know the awesome benchmark u made on neo N3. Actually I always wanna know what exactly makes C# slower than go node. But anyway, benchmark won't stop resource exhaustion attack, strict gas restrictions may work, I will check it out.

[roman-khimov]

DoS scenarios are always limited by GAS, sending lots of transactions costs something and it's not hard to calculate the cost of the attack. Actually, this change raises the cost of the attack because to cause some noticeable delays one would need to send more transactions and spend more GAS.

As for computational overhead of big blocks, MaxBlockSystemFee is big enough already to be noticeable and if someone has enough GAS to spend he might keep the nodes somewhat busy even with a single transaction (just ask @vang1ong7ang). But then again, the attacker is limited by the amount of GAS (money) he has for attack.

[Jim8y]

I understand. You can keep working on this pr, I will do a thorough benchmark on opcodes in another work.

[roman-khimov]

I will do a thorough benchmark on opcodes in another work.

Take a look at neo-project/neo#1875 also, although both VMs have improved since then I think.

[Jim8y]

Take a look at neo-project/neo#1875

Thank you.

[superboyiii]

@roman-khimov Could you push it to develop branch? We'd like to keep master clear before next release.

[roman-khimov]

@roman-khimov Could you push it to develop branch?

Sure, done.