From 5bf4f26319d4b522dcb7c08cb2f2dbfc65a8aeb7 Mon Sep 17 00:00:00 2001
From: lodekeeper <lodekeeper@users.noreply.github.com>
Date: Thu, 4 Jun 2026 18:00:11 +0000
Subject: [PATCH] fix(beacon-node): publish only subscribed columns from
 reconstruction
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Mirror the getBlobsV2 path in getDataColumnSidecarsFromExecution and align
with Lighthouse/Prysm by publishing only sampled (custody + sampling)
columns after matrix recovery, instead of cross-seeding every recovered
column to non-subscribed subnets.

Per consensus-specs PR #4657, eager fanout for non-custody columns floods
the network with duplicates because the sender lacks visibility into which
peers already saw the message via the topic mesh. A node custodying 65
columns ends up publishing at least 64 (63 non-custody + 1 missing custody)
columns every reconstruction, which is more outbound bandwidth than a
supernode.

Refs: https://github.com/ethereum/consensus-specs/pull/4657

🤖 Generated with AI assistance
---
 packages/beacon-node/src/util/dataColumns.ts | 29 ++++++++++++--------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/packages/beacon-node/src/util/dataColumns.ts b/packages/beacon-node/src/util/dataColumns.ts
index 98a1aa52ba05..3e79a44639ce 100644
--- a/packages/beacon-node/src/util/dataColumns.ts
+++ b/packages/beacon-node/src/util/dataColumns.ts
@@ -470,15 +470,17 @@ export async function recoverDataColumnSidecars(
     return DataColumnReconstructionCode.SuccessLate;
   }
 
-  // Once the node obtains a column through reconstruction,
-  // the node MUST expose the new column as if it had received it over the network.
-  // If the node is subscribed to the subnet corresponding to the column,
-  // it MUST send the reconstructed DataColumnSidecar to its topic mesh neighbors.
-  // If instead the node is not subscribed to the corresponding subnet,
-  // it SHOULD still expose the availability of the DataColumnSidecar as part of the gossip emission process.
-  // After exposing the reconstructed DataColumnSidecar to the network,
-  // the node MAY delete the DataColumnSidecar if it is not part of the node's custody requirement.
-  const sidecarsToPublish = [];
+  // Per consensus-specs PR #4657, only publish reconstructed columns the node is
+  // subscribed to (custody + sampling). Eagerly cross-seeding non-subscribed
+  // columns floods the network with duplicates because the sender has no
+  // visibility into which peers already saw the message via the topic mesh.
+  // This matches the getBlobsV2 path in `getDataColumnSidecarsFromExecution` and
+  // aligns with Lighthouse/Prysm. Capture missing sampled indices before adding
+  // any reconstructed columns so they are not filtered out by the subsequent
+  // `addColumn` calls.
+  const missingSampledColumns = new Set(input.getMissingSampledColumnMeta().missing);
+  const sidecarsReconstructed: DataColumnSidecar[] = [];
+  const sidecarsToPublish: DataColumnSidecar[] = [];
   for (const columnSidecar of fullSidecars) {
     if (!input.hasColumn(columnSidecar.index)) {
       if (input instanceof PayloadEnvelopeInput) {
@@ -501,11 +503,14 @@ export async function recoverDataColumnSidecars(
           source: BlockInputSource.recovery,
         });
       }
-      sidecarsToPublish.push(columnSidecar);
+      sidecarsReconstructed.push(columnSidecar);
+      if (missingSampledColumns.has(columnSidecar.index)) {
+        sidecarsToPublish.push(columnSidecar);
+      }
     }
   }
-  metrics?.peerDas.reconstructedColumns.inc(sidecarsToPublish.length);
-  metrics?.dataColumns.bySource.inc({source: BlockInputSource.recovery}, sidecarsToPublish.length);
+  metrics?.peerDas.reconstructedColumns.inc(sidecarsReconstructed.length);
+  metrics?.dataColumns.bySource.inc({source: BlockInputSource.recovery}, sidecarsReconstructed.length);
   emitter.emit(ChainEvent.publishDataColumns, sidecarsToPublish);
   // TODO: Can we record dataColumns.sentPeersPerSubnet metric somehow
   return DataColumnReconstructionCode.SuccessResolved;