Prune pending deposits from the deposit cache post-Electra

[syjn99]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

After conversations with @james-prysm and @nisdas at #14698, this will be a first step to mitigate an memory effect after post-Electra.
This PR adds DepositPruner, which prunes all pending deposits and proofs after Electra(when legacy eth1 polling is deprecated). a7eae66 moves some functions in deposit_fetcher.go into deposit_pruner.go, as it seems more suitable. deposit_pruner.go might contain pruning whole deposits, but I thought that it could be handled at other PRs.

I did some experiment on local devnet. I spammed deposit transactions at those devnets, and here's the metrics:

Normally, after post-Electra, pending deposits are not pruned at all, it leads pending deposits to infinitely grow like the panel shows.

When this PR applied, pending deposits are pruned(Red line) at every finalization event. (You can see the config file for kurtosis at this gist.) depositsnapshot doesn't affect the consensus after post-Electra at all.

Which issues(s) does this PR fix?

Resolves #14698

Other notes for review

Adding DepositPruner could be quite controversial, so feedbacks are welcomed.

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description to this PR with sufficient context for reviewers to understand this PR.

[james-prysm]

Electra will be looking to release in the next month , we would like to get this into the release depending on your findings with testing. we mostlikely will be releasing in testnet without this feature yet.

[syjn99]

@james-prysm Yes, I agree to the point. Then I'll keep this PR in draft mode.

[james-prysm]

please let us know if you think this will be ready in the next few weeks for mainnet 🙏 thank you for the work

[syjn99]

@james-prysm
Thanks! Observing a Grafana dashboard with two metrics would be feasible.

• beacondb_pending_deposits_eip4881
• beacondb_all_deposits_eip4881

[james-prysm]

@syjn99 we're going to try to get this into the release for testnet actually. I'll see if I can pick up where you left off here if nishant had any comments. he'll review tomorrow and we'll get this merged. please let us know if there are any concerns.

[james-prysm]

@syjn99 are you able to let me push changes directly to your branch? otherwise I can create a fork of your branch I think or start a new one with acknowledgment to you

[syjn99]

@james-prysm Just pushed a commit that applies all reviews from team!

[james-prysm]

@syjn99 looks like unit tests are failing Test_executePostFinalizationTasks

I think that's a test I added in the past, it's an electra state 😓 so I guess it shouldn't have that log anymore

[syjn99]

@james-prysm How about adding test cases, and separating them into pre-Electra and post-Electra?

[james-prysm]

I think this is silly... there's a bug I think, because it's a fake state eth1depositindex of 0 is the same as the requests start index of 0

I don't think that's possible in any other state but probably a bug with this test not using realistic values.

// DepositRequestsStarted determines if the deposit requests have started.
func DepositRequestsStarted(beaconState state.BeaconState) bool {
	if beaconState.Version() < version.Electra {
		return false
	}

	requestsStartIndex, err := beaconState.DepositRequestsStartIndex()
	if err != nil {
		return false
	}
       
	return beaconState.Eth1DepositIndex() == requestsStartIndex
}

[james-prysm]

maybe this is still too much copy paste, just wanted to fix it

[james-prysm]

@syjn99 Thanks for your work on this ! it was a great catch, we'll get this merged