private void destroySubscription(final long subscriptionId) {
    final Subscription removed = subscriptions.remove(subscriptionId);
    if (removed != null) {
      unsubscribeCounter.labels(removed.getSubscriptionType().getCode()).inc();
    }
  }
The SubscriptionManager is responsible for managing subscriptions and sending messages to the
clients that have an active subscription.
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/websocket/subscription/SubscriptionManager.java