public void await() {
        try {
            while (inflight.get() > 0) Thread.sleep(10);
            resettableCluster.sync();
        }
        catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
Retries throttled requests (429), adjusting the target inflight count, and server unavailable (503).
vespa-feed-client/src/main/java/ai/vespa/feed/client/impl/HttpRequestStrategy.java