static void logResponse(Level level, HttpResponse response, HttpRequest request, int attempt) {
        if (log.isLoggable(level))
            log.log(level, "Status code " + response.code() +
                           " (" + (response.body() == null ? "no body" : new String(response.body(), UTF_8)) +
                           ") on attempt " + attempt + " at " + request);
    }
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