fix(distributor): Disable metadata topic writes (#17437)

Author: periklis

pkg/distributor/distributor.go

@@ -1269,7 +1269,7 @@ func (d *Distributor) sendStreamToKafka(ctx context.Context, stream KeyedStream,
 
 	entriesSize, structuredMetadataSize := calculateStreamSizes(stream.Stream)
 
-	if _, ok := skipMetadataHashes[stream.HashKeyNoShard]; !ok {
+	if _, ok := skipMetadataHashes[stream.HashKeyNoShard]; !ok && d.cfg.IngestLimitsEnabled {
 		// However, unlike stream records, the distributor writes stream metadata
 		// records to one of a fixed number of partitions, the size of which is
 		// determined ahead of time. It does not use a ring. The reason for this

pkg/distributor/distributor_test.go

@@ -2645,9 +2645,7 @@ func TestDistributor_SkipMetadataHashes(t *testing.T) {
 				}},
 			}},
 		},
-		// For now, metadata records are still written when
-		// limits are disabled in distributors.
-		expectedMetadataRecords: 1,
+		expectedMetadataRecords: 0,
 	}, {
 		name:                "limits are enabled",
 		ingestLimitsEnabled: true,