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feat: implement shuffling cache (#6030)
* feat: implement ShufflingCache * fix: get shuffling decision block at genesis state * chore: use flatMap()
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,193 @@ | ||
| import {toHexString} from "@chainsafe/ssz"; | ||
| import {CachedBeaconStateAllForks, EpochShuffling, getShufflingDecisionBlock} from "@lodestar/state-transition"; | ||
| import {Epoch, RootHex, ssz} from "@lodestar/types"; | ||
| import {MapDef, pruneSetToMax} from "@lodestar/utils"; | ||
| import {GENESIS_SLOT} from "@lodestar/params"; | ||
| import {Metrics} from "../metrics/metrics.js"; | ||
| import {computeAnchorCheckpoint} from "./initState.js"; | ||
|
|
||
| /** | ||
| * Same value to CheckpointBalancesCache, with the assumption that we don't have to use it for old epochs. In the worse case: | ||
| * - when loading state bytes from disk, we need to compute shuffling for all epochs (~1s as of Sep 2023) | ||
| * - don't have shuffling to verify attestations, need to do 1 epoch transition to add shuffling to this cache. This never happens | ||
| * with default chain option of maxSkipSlots = 32 | ||
| **/ | ||
| const MAX_EPOCHS = 4; | ||
|
|
||
| /** | ||
| * With default chain option of maxSkipSlots = 32, there should be no shuffling promise. If that happens a lot, it could blow up Lodestar, | ||
| * with MAX_EPOCHS = 4, only allow 2 promise at a time. Note that regen already bounds number of concurrent requests at 1 already. | ||
| */ | ||
| const MAX_PROMISES = 2; | ||
|
|
||
| enum CacheItemType { | ||
| shuffling, | ||
| promise, | ||
| } | ||
|
|
||
| type ShufflingCacheItem = { | ||
| type: CacheItemType.shuffling; | ||
| shuffling: EpochShuffling; | ||
| }; | ||
|
|
||
| type PromiseCacheItem = { | ||
| type: CacheItemType.promise; | ||
| promise: Promise<EpochShuffling>; | ||
| resolveFn: (shuffling: EpochShuffling) => void; | ||
| }; | ||
|
|
||
| type CacheItem = ShufflingCacheItem | PromiseCacheItem; | ||
|
|
||
| export type ShufflingCacheOpts = { | ||
| maxShufflingCacheEpochs?: number; | ||
| }; | ||
|
|
||
| /** | ||
| * A shuffling cache to help: | ||
| * - get committee quickly for attestation verification | ||
| * - if a shuffling is not available (which does not happen with default chain option of maxSkipSlots = 32), track a promise to make sure we don't compute the same shuffling twice | ||
| * - skip computing shuffling when loading state bytes from disk | ||
| */ | ||
| export class ShufflingCache { | ||
| /** LRU cache implemented as a map, pruned every time we add an item */ | ||
| private readonly itemsByDecisionRootByEpoch: MapDef<Epoch, Map<RootHex, CacheItem>> = new MapDef( | ||
| () => new Map<RootHex, CacheItem>() | ||
| ); | ||
|
|
||
| private readonly maxEpochs: number; | ||
|
|
||
| constructor( | ||
| private readonly metrics: Metrics | null = null, | ||
| opts: ShufflingCacheOpts = {} | ||
| ) { | ||
| if (metrics) { | ||
| metrics.shufflingCache.size.addCollect(() => | ||
| metrics.shufflingCache.size.set( | ||
| Array.from(this.itemsByDecisionRootByEpoch.values()).reduce((total, innerMap) => total + innerMap.size, 0) | ||
| ) | ||
| ); | ||
| } | ||
|
|
||
| this.maxEpochs = opts.maxShufflingCacheEpochs ?? MAX_EPOCHS; | ||
| } | ||
|
|
||
| /** | ||
| * Extract shuffling from state and add to cache | ||
| */ | ||
| processState(state: CachedBeaconStateAllForks, shufflingEpoch: Epoch): EpochShuffling { | ||
| const decisionBlockHex = getDecisionBlock(state, shufflingEpoch); | ||
| let shuffling: EpochShuffling; | ||
| switch (shufflingEpoch) { | ||
| case state.epochCtx.nextShuffling.epoch: | ||
| shuffling = state.epochCtx.nextShuffling; | ||
| break; | ||
| case state.epochCtx.currentShuffling.epoch: | ||
| shuffling = state.epochCtx.currentShuffling; | ||
| break; | ||
| case state.epochCtx.previousShuffling.epoch: | ||
| shuffling = state.epochCtx.previousShuffling; | ||
| break; | ||
| default: | ||
| throw new Error(`Shuffling not found from state ${state.slot} for epoch ${shufflingEpoch}`); | ||
| } | ||
|
|
||
| let cacheItem = this.itemsByDecisionRootByEpoch.getOrDefault(shufflingEpoch).get(decisionBlockHex); | ||
| if (cacheItem !== undefined) { | ||
| // update existing promise | ||
| if (isPromiseCacheItem(cacheItem)) { | ||
| // unblock consumers of this promise | ||
| cacheItem.resolveFn(shuffling); | ||
| // then update item type to shuffling | ||
| cacheItem = { | ||
| type: CacheItemType.shuffling, | ||
| shuffling, | ||
| }; | ||
| this.add(shufflingEpoch, decisionBlockHex, cacheItem); | ||
| // we updated type to CacheItemType.shuffling so the above fields are not used anyway | ||
| this.metrics?.shufflingCache.processStateUpdatePromise.inc(); | ||
| } else { | ||
| // ShufflingCacheItem, do nothing | ||
| this.metrics?.shufflingCache.processStateNoOp.inc(); | ||
| } | ||
| } else { | ||
| // not found, new shuffling | ||
| this.add(shufflingEpoch, decisionBlockHex, {type: CacheItemType.shuffling, shuffling}); | ||
| this.metrics?.shufflingCache.processStateInsertNew.inc(); | ||
| } | ||
|
|
||
| return shuffling; | ||
| } | ||
|
|
||
| /** | ||
| * Insert a promise to make sure we don't regen state for the same shuffling. | ||
| * Bound by MAX_SHUFFLING_PROMISE to make sure our node does not blow up. | ||
| */ | ||
| insertPromise(shufflingEpoch: Epoch, decisionRootHex: RootHex): void { | ||
| const promiseCount = Array.from(this.itemsByDecisionRootByEpoch.values()) | ||
| .flatMap((innerMap) => Array.from(innerMap.values())) | ||
| .filter((item) => isPromiseCacheItem(item)).length; | ||
| if (promiseCount >= MAX_PROMISES) { | ||
| throw new Error( | ||
| `Too many shuffling promises: ${promiseCount}, shufflingEpoch: ${shufflingEpoch}, decisionRootHex: ${decisionRootHex}` | ||
| ); | ||
| } | ||
| let resolveFn: ((shuffling: EpochShuffling) => void) | null = null; | ||
| const promise = new Promise<EpochShuffling>((resolve) => { | ||
| resolveFn = resolve; | ||
| }); | ||
| if (resolveFn === null) { | ||
| throw new Error("Promise Constructor was not executed immediately"); | ||
| } | ||
|
|
||
| const cacheItem: PromiseCacheItem = { | ||
| type: CacheItemType.promise, | ||
| promise, | ||
| resolveFn, | ||
| }; | ||
| this.add(shufflingEpoch, decisionRootHex, cacheItem); | ||
| this.metrics?.shufflingCache.insertPromiseCount.inc(); | ||
| } | ||
|
|
||
| /** | ||
| * Most of the time, this should return a shuffling immediately. | ||
| * If there's a promise, it means we are computing the same shuffling, so we wait for the promise to resolve. | ||
| * Return null if we don't have a shuffling for this epoch and dependentRootHex. | ||
| */ | ||
| async get(shufflingEpoch: Epoch, decisionRootHex: RootHex): Promise<EpochShuffling | null> { | ||
| const cacheItem = this.itemsByDecisionRootByEpoch.getOrDefault(shufflingEpoch).get(decisionRootHex); | ||
| if (cacheItem === undefined) { | ||
| return null; | ||
| } | ||
|
|
||
| if (isShufflingCacheItem(cacheItem)) { | ||
| return cacheItem.shuffling; | ||
| } else { | ||
| // promise | ||
| return cacheItem.promise; | ||
| } | ||
| } | ||
|
|
||
| private add(shufflingEpoch: Epoch, decisionBlock: RootHex, cacheItem: CacheItem): void { | ||
| this.itemsByDecisionRootByEpoch.getOrDefault(shufflingEpoch).set(decisionBlock, cacheItem); | ||
| pruneSetToMax(this.itemsByDecisionRootByEpoch, this.maxEpochs); | ||
| } | ||
| } | ||
|
|
||
| function isShufflingCacheItem(item: CacheItem): item is ShufflingCacheItem { | ||
| return item.type === CacheItemType.shuffling; | ||
| } | ||
|
|
||
| function isPromiseCacheItem(item: CacheItem): item is PromiseCacheItem { | ||
| return item.type === CacheItemType.promise; | ||
| } | ||
|
|
||
| /** | ||
| * Get the shuffling decision block root for the given epoch of given state | ||
| * - Special case close to genesis block, return the genesis block root | ||
| * - This is similar to forkchoice.getDependentRoot() function, otherwise we cannot get cached shuffing in attestation verification when syncing from genesis. | ||
| */ | ||
| function getDecisionBlock(state: CachedBeaconStateAllForks, epoch: Epoch): RootHex { | ||
| return state.slot > GENESIS_SLOT | ||
| ? getShufflingDecisionBlock(state, epoch) | ||
| : toHexString(ssz.phase0.BeaconBlockHeader.hashTreeRoot(computeAnchorCheckpoint(state.config, state).blockHeader)); | ||
| } |
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