Evict transactions from the mempool based on the ZIP-317 fee rules

[teor2345]

Motivation

We can deploy the new mempool rules in ZIP-317 before wallets have updated to the new conventional fee, because dropping transactions is randomised.

This can be changed in Zebra at any time. It must not be behind the getblocktemplate-rpcs feature, because it is required as soon as possible to mitigate denial of service:
https://zips.z.cash/zip-0317#deployment

Specification

The conventional fee part of:
https://zips.z.cash/zip-0317

[dconnolly]

We can deploy the new mempool rules in ZIP-317 before wallets have updated to the new conventional fee, because dropping transactions is randomised.

This can be changed in Zebra at any time.

Correct, yes. Some more context on why this is true:

'The eviction weight is already proportional to the size of the transaction in bytes', so we should be able to deploy these changes before wallets do without negative effect (per daira). What will happen in practice is regardless of whether an attacker chooses big transactions or lots of smaller transactions, the total size of their transactions will be large compared to the legitimate ones, it will always be more likely that the adv. 's transactions will be dropped vs legitimate ones. // @daira

[teor2345]

@mpguerra this ZIP is now approved. Can we schedule this change in the next sprint, or at the end of this sprint if we have time?

It is an important change to mitigate the ongoing transaction spam on the network.

[mpguerra]

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