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1bffcc84f4
**What type of PR is this?**
Optimisation (@nisdas)
**What does this PR do? Why is it needed?**
The beacon state contains the list of all validators that have been at
least once deposited on the network.
| Network | Active | Total | Ratio |
|----------|-----------|---------------|---------|
| Hoodi | 1,224,855 | **1,294,521** | 94.1% |
| Mainnet | 948,883 | **2,229,313** | 43.56% |
Currently, the validators are stored in the beacon state like this:
```go
type BeaconState struct {
...
validatorsMultiValue *MultiValueValidators
...
}
type MultiValueValidators = multi_value_slice.Slice[*ethpb.Validator]
type Validator struct {
state protoimpl.MessageState `protogen:"open.v1"`
PublicKey []byte `protobuf:"bytes,1,opt,name=public_key,json=publicKey,proto3" json:"public_key,omitempty" spec-name:"pubkey" ssz-size:"48"`
WithdrawalCredentials []byte `protobuf:"bytes,2,opt,name=withdrawal_credentials,json=withdrawalCredentials,proto3" json:"withdrawal_credentials,omitempty" ssz-size:"32"`
EffectiveBalance uint64 `protobuf:"varint,3,opt,name=effective_balance,json=effectiveBalance,proto3" json:"effective_balance,omitempty"`
Slashed bool `protobuf:"varint,4,opt,name=slashed,proto3" json:"slashed,omitempty"`
ActivationEligibilityEpoch github_com_OffchainLabs_prysm_v7_consensus_types_primitives.Epoch `protobuf:"varint,5,opt,name=activation_eligibility_epoch,json=activationEligibilityEpoch,proto3" json:"activation_eligibility_epoch,omitempty" cast-type:"github.com/OffchainLabs/prysm/v7/consensus-types/primitives.Epoch"`
ActivationEpoch github_com_OffchainLabs_prysm_v7_consensus_types_primitives.Epoch `protobuf:"varint,6,opt,name=activation_epoch,json=activationEpoch,proto3" json:"activation_epoch,omitempty" cast-type:"github.com/OffchainLabs/prysm/v7/consensus-types/primitives.Epoch"`
ExitEpoch github_com_OffchainLabs_prysm_v7_consensus_types_primitives.Epoch `protobuf:"varint,7,opt,name=exit_epoch,json=exitEpoch,proto3" json:"exit_epoch,omitempty" cast-type:"github.com/OffchainLabs/prysm/v7/consensus-types/primitives.Epoch"`
WithdrawableEpoch github_com_OffchainLabs_prysm_v7_consensus_types_primitives.Epoch `protobuf:"varint,8,opt,name=withdrawable_epoch,json=withdrawableEpoch,proto3" json:"withdrawable_epoch,omitempty" cast-type:"github.com/OffchainLabs/prysm/v7/consensus-types/primitives.Epoch"`
unknownFields protoimpl.UnknownFields
sizeCache protoimpl.SizeCache
}
```
Some fields, used only by protobuf (`state`, `unknownFields`,
`sizeCache`) are not used by the beacon node.
Some other fields, stored as slices (`PublicKey`,
`WithdrawalCredentials`) need extra memory (`ptr+len+cap`) while they
could be stored as arrays because their sizes are fixed and known in
advance.
We define a new custom type called `CompactValidator`, which is a
fixed-size, pointer-free representation of a validator:
```go
type CompactValidator struct {
PublicKey [fieldparams.BLSPubkeyLength]byte // 48 bytes
WithdrawalCredentials [32]byte // 32 bytes
EffectiveBalance uint64 // 8 bytes
Slashed bool // 1 byte
ActivationEligibilityEpoch primitives.Epoch // 8 bytes
ActivationEpoch primitives.Epoch // 8 bytes
ExitEpoch primitives.Epoch // 8 bytes
WithdrawableEpoch primitives.Epoch // 8 bytes
}
```
Here is the comparison, per validator, between storing a
`*ethpb.Validator` and a `CompactValidator`.
| Component | `*ethpb.Validator` | `CompactValidator` | Wasted |
|------------------------------------------|--------------------|--------------------|---------|
| Pointer to struct | 8 B | 0 B | 8 B |
| `state` (protoimpl.MessageState) | 8 B | 0 B | 8 B |
| `PublicKey` slice header (ptr+len+cap) | 24 B | 0 B | 24 B |
| `PublicKey` backing array (heap) | 48 B | 48 B (inline) | 0 B |
| `PublicKey` malloc overhead | ~16 B | 0 B | ~16 B |
| `WithdrawalCredentials` slice header | 24 B | 0 B | 24 B |
| `WithdrawalCredentials` backing array | 32 B | 32 B (inline) | 0 B |
| `WithdrawalCredentials` malloc overhead | ~16 B | 0 B | ~16 B |
| `EffectiveBalance` (uint64) | 8 B | 8 B | 0 B |
| `Slashed` (bool + padding) | 8 B | 8 B | 0 B |
| `ActivationEligibilityEpoch` | 8 B | 8 B | 0 B |
| `ActivationEpoch` | 8 B | 8 B | 0 B |
| `ExitEpoch` | 8 B | 8 B | 0 B |
| `WithdrawableEpoch` | 8 B | 8 B | 0 B |
| `unknownFields` ([]byte header) | 24 B | 0 B | 24 B |
| `sizeCache` (int32 + padding) | 8 B | 0 B | 8 B |
| Struct malloc overhead | ~16 B | 0 B | ~16 B |
| **Total** | **~264 B** | **128 B** | **~136 B (52%)** |
We waste `~136 B` per validator.
With a total of `2,229,313` validators (mainnet), it represents `~290
MB`.
Storing `CompactValidator` instead of `*ethpb.Validator` also reduces
the garbage collection pressure.
The following graph represents, for a Hoodi supernode (200 validators
managed):
1. The heap memory usage (`go_memstats_alloc_bytes`) without this PR
(`ref`) and with this PR (`current`)
2. `1.`, but averaged over the latest four hours.
3. The diff of the graphs in `2`. (The bigger, the better)
> [!NOTE]
> The improvement is, after stabilisation, **~300MB-450MB**,
representing **~8%-11%**.
>
> <img width="1028" height="917" alt="image"
src="https://github.com/user-attachments/assets/9179d9b1-bc50-4248-9f47-82a7646d58ab"
/>
>
> For some reasons, the gain is higher than initialy expected.
**For the reviewers:**
This PR should be reviewed commit by commit:
Commits 1 and 2 are independent and unrelated to this PR
Commit 3 is an oversight of:
- https://github.com/OffchainLabs/prysm/pull/16420
Commit 4 implements the `CompactValidator`
Commit 5 uses the `CompactValidator`. The key change is:
```go
// MultiValueValidators is a multi-value slice of compact validators.
type MultiValueValidators = multi_value_slice.Slice[stateutil.CompactValidator]
```
**Acknowledgements**
- [x] I have read
[CONTRIBUTING.md](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md).
- [x] I have included a uniquely named [changelog fragment
file](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md#maintaining-changelogmd).
- [x] I have added a description with sufficient context for reviewers
to understand this PR.
- [x] I have tested that my changes work as expected and I added a
testing plan to the PR description (if applicable).
---------
Co-authored-by: Bastin <43618253+Inspector-Butters@users.noreply.github.com>
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