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fix: bound SeenPayloadEnvelopeInput cache size to prevent OOM #9489

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fix: bound SeenPayloadEnvelopeInput cache size to prevent OOM #9489

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8f42a36
fix: bound `SeenPayloadEnvelopeInput` cache size to prevent OOM
nflaig Jun 9, 2026
e5274f2
fix: exclude just-inserted entry from `SeenPayloadEnvelopeInput` pruning
nflaig Jun 9, 2026
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33 changes: 33 additions & 0 deletions packages/beacon-node/src/chain/seenCache/seenPayloadEnvelopeInput.ts
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Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
import {ChainForkConfig} from "@lodestar/config";
import {CheckpointWithHex, IForkChoice, ProtoBlock} from "@lodestar/fork-choice";
import {SLOTS_PER_EPOCH} from "@lodestar/params";
import {computeStartSlotAtEpoch} from "@lodestar/state-transition";
import {RootHex} from "@lodestar/types";
import {Logger} from "@lodestar/utils";
import {Metrics} from "../../metrics/metrics.js";
import {MAX_LOOK_AHEAD_EPOCHS} from "../../sync/constants.js";
import {IClock} from "../../util/clock.js";
import {SerializedCache} from "../../util/serializedCache.js";
import {isDaOutOfRange} from "../blocks/blockInput/index.js";
Expand All @@ -24,6 +26,13 @@ export type SeenPayloadEnvelopeInputModules = {
logger?: Logger;
};

// Upper bound on the cache, enforced on every insertion. pruneFinalized / pruneBelowParent are both
// dormant during catch-up (no finality; prepareNextSlot bails once the head is far behind the clock),
// so without an insert-time cap the cache grows unbounded and OOMs the node
// (see https://github.com/ChainSafe/lodestar/issues/9073). Same size as SeenBlockInput's
// MAX_BLOCK_INPUT_CACHE_SIZE.
const MAX_PAYLOAD_ENVELOPE_INPUT_CACHE_SIZE = (MAX_LOOK_AHEAD_EPOCHS + 1) * SLOTS_PER_EPOCH;

/**
* Cache for tracking PayloadEnvelopeInput instances, keyed by beacon block root.
*
Expand Down Expand Up @@ -116,6 +125,7 @@ export class SeenPayloadEnvelopeInput {
root: props.blockRootHex,
daOutOfRange,
});
this.pruneToMaxSize(props.blockRootHex);
return input;
}

Expand All @@ -137,6 +147,7 @@ export class SeenPayloadEnvelopeInput {
root: props.blockRootHex,
daOutOfRange,
});
this.pruneToMaxSize(props.blockRootHex);
return input;
}

Expand Down Expand Up @@ -167,6 +178,28 @@ export class SeenPayloadEnvelopeInput {
}
}

/**
* Enforce the size cap by evicting the lowest-slot entry (oldest / furthest behind the head).
* Called on every insertion so the cache is at most one over the cap. `excludeRoot` is never
* evicted, so an add can't remove itself when it is the lowest slot (e.g. an older block in a reorg).
*/
private pruneToMaxSize(excludeRoot?: RootHex): void {

@nflaig nflaig Jun 9, 2026

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@lodekeeper can you confirm whether this exclude root is even needed, in what scenario can this be relevant with our current code?

@lodekeeper lodekeeper Jun 9, 2026

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Walked the 5 add / addFromBid call sites for the scenario where the just-inserted entry's slot is the strict minimum in the cache (the only case where excludeRoot actually fires):

Caller Slot of insert Hits excludeRoot?
chain.ts:445 (addFromBid at init) anchor block slot No — cache is empty at init, no eviction can fire
gossipHandlers.ts:191 (gossip block) gossip-window slot Yes, but only when finalized_slot < head - 96 (stalled finality) AND the block is on a non-canonical fork at a slot lower than every cache entry — validateGossipBlock lets that range through
downloadByRange.ts:214 (range sync seed) batch epoch slot Yes for out-of-order batch completion (Codex P1) — but excludeRoot only protects the single entry being added in this call; sibling adds earlier in the same batch can still get evicted by the next add. Partial coverage.
downloadByRoot.ts:119 (parent root sync) parent slot Yes for deep-reorg / fork-recovery where the parent is significantly older than head, edge case
api/impl/beacon/blocks/index.ts:116 (publish API) near-head slot No — validator-published blocks are at or near current slot

So it's reachable but only in three narrow regimes: stalled-finality gossip on a low-slot non-canonical fork, out-of-order range-sync batches, and deep-reorg parent fetches.

One extra wrinkle worth flagging: even when excludeRoot fires, the protection only lasts until the next add() call — that next add doesn't know to exclude the previous entry, so it becomes the new lowest and gets evicted. So excludeRoot is at most a 1-tick reprieve. For the gossip case in particular, the gap between gossipHandlers.ts:191 (block add) and the matching envelope lookup at gossipHandlers.ts:1141 (PAYLOAD_ENVELOPE_INPUT_MISSING throw) can easily span several other gossip adds in a busy network, in which case excludeRoot doesn't actually save the lookup.

Verdict: defensible to keep — costs almost nothing, plugs the immediate self-eviction path that the unit test exercises. But fair to drop too if you'd rather simplify; the OOM scenario this PR addresses (sequential catch-up) never enters the excludeRoot branch since adds are always at the high end of the slot range. If we drop it I'd suggest a brief comment on pruneToMaxSize noting that a single low-slot insert can be self-evicting, so callers shouldn't assume add() always succeeds.

If you want a stronger guarantee for the gossip-block → envelope path specifically, the real fix is either (a) skip-prune on add and prune at a clock-tick boundary, or (b) the local seed-map fallback in cacheByRangeResponses Codex suggested — both follow-up scope.

while (this.payloadInputs.size > MAX_PAYLOAD_ENVELOPE_INPUT_CACHE_SIZE) {
let lowest: PayloadEnvelopeInput | undefined;
for (const input of this.payloadInputs.values()) {
if (input.blockRootHex === excludeRoot) continue;
if (lowest === undefined || input.slot < lowest.slot) lowest = input;
}
if (lowest === undefined) break;
this.evictPayloadInput(lowest);
this.logger?.debug("SeenPayloadEnvelopeInput.pruneToMaxSize evicted entry", {
slot: lowest.slot,
root: lowest.blockRootHex,
maxSize: MAX_PAYLOAD_ENVELOPE_INPUT_CACHE_SIZE,
});
}
}

private evictPayloadInput(payloadInput: PayloadEnvelopeInput): void {
this.serializedCache.delete(payloadInput.getSerializedCacheKeys());
this.payloadInputs.delete(payloadInput.blockRootHex);
Expand Down
40 changes: 39 additions & 1 deletion packages/beacon-node/test/unit/chain/seenCache/seenPayloadEnvelopeInput.test.ts
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Original file line number Diff line number Diff line change
@@ -1,11 +1,12 @@
import {beforeEach, describe, expect, it, vi} from "vitest";
import {ExecutionStatus, IForkChoice, PayloadStatus, ProtoBlock} from "@lodestar/fork-choice";
import {testLogger} from "@lodestar/logger/test-utils";
import {ForkName} from "@lodestar/params";
import {ForkName, SLOTS_PER_EPOCH} from "@lodestar/params";
import {DataAvailabilityStatus} from "@lodestar/state-transition";
import {RootHex} from "@lodestar/types";
import {ChainEventEmitter} from "../../../../src/chain/emitter.js";
import {SeenPayloadEnvelopeInput} from "../../../../src/chain/seenCache/seenPayloadEnvelopeInput.js";
import {MAX_LOOK_AHEAD_EPOCHS} from "../../../../src/sync/constants.js";
import {SerializedCache} from "../../../../src/util/serializedCache.js";
import {getMockedClock} from "../../../mocks/clock.js";
import {config, generateBlock} from "../../../utils/blocksAndData.js";
Expand Down Expand Up @@ -96,6 +97,43 @@ describe("SeenPayloadEnvelopeInput", () => {
expect(cache.get(rootHex)).toBeDefined();
});

it("pruneToMaxSize bounds the cache on insertion, evicting the lowest-slot entries", () => {
// pruneFinalized / pruneBelowParent never run here, so the insertion-time cap is the only bound
const maxSize = (MAX_LOOK_AHEAD_EPOCHS + 1) * SLOTS_PER_EPOCH;
const overflow = 5;

const rootHexBySlot = new Map<number, string>();
for (let slot = 1; slot <= maxSize + overflow; slot++) {
rootHexBySlot.set(slot, addPayloadInput(slot));
}

// never grows past the cap despite no finality-based pruning
expect(cache.size()).toBe(maxSize);

// the oldest (lowest-slot) entries are evicted ...
for (let slot = 1; slot <= overflow; slot++) {
expect(cache.get(rootHexBySlot.get(slot) as string)).toBeUndefined();
}
// ... and the most recent window is retained
for (let slot = overflow + 1; slot <= maxSize + overflow; slot++) {
expect(cache.get(rootHexBySlot.get(slot) as string)).toBeDefined();
}
});

it("excludes the just-inserted entry from pruning even when it is the lowest slot", () => {
const maxSize = (MAX_LOOK_AHEAD_EPOCHS + 1) * SLOTS_PER_EPOCH;
const prevLowest = addPayloadInput(101);
for (let slot = 102; slot < 101 + maxSize; slot++) addPayloadInput(slot);
expect(cache.size()).toBe(maxSize);

// adding an older block (lowest slot) while at cap must not evict itself; the previous lowest
// (slot 101) is evicted instead. Guards the reorg / older-fork case.
const older = addPayloadInput(1);
expect(cache.size()).toBe(maxSize);
expect(cache.get(older)).toBeDefined();
expect(cache.get(prevLowest)).toBeUndefined();
});

it("add returns the existing entry on duplicate root", () => {
const {block, rootHex} = generateBlock({forkName: ForkName.gloas, slot: 1});
const props = {
Expand Down
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