Server[ ] might not yet be synced successfully. We will…

Error message

Server[%s] might not yet be synced successfully. We will continue to retry that in the background.

What it means

HttpServerInventoryView.serverInventoryInitialized logs a warning listing servers that had not completed at least one successful inventory sync when initialization completed. It means the view's server list is incomplete and it will keep retrying those servers in the background.

Solutions

Verify the listed servers are running and reachable on their druid.host:port from this node
Check the historicals' logs for errors serving /druid-internal/v1/listSorting... inventory endpoints
Fix network/DNS/firewall issues between the coordinator/broker and the historicals
Confirm druid.serverview.* http timeouts are adequate for large segment counts; restart the view holder after fixing connectivity

Example fix

// before
druid.host=10.0.0.5:8083 // unreachable internal IP
// after
druid.host=cluster-internal-5.druid.svc:8083 // resolvable, routable from coordinators/brokers

Defensive patterns

Strategy: retry

Validate before calling

// probe server reachability before startup completion
boolean healthy = ping(serverHost, serverPort, timeoutMs);

Try / catch

// rely on built-in background retry; monitor logs
await at most N seconds, then re-check uninitialized servers and alert if still unsynced

Prevention

Ensure historicals are up before brokers/coordinators finish initialization
Use resolvable, routable druid.host values
Open firewall paths for inventory HTTP endpoints
Increase server inventory HTTP timeouts for large clusters

When it happens

Trigger: serverInventoryInitialized fired while some historicals never returned a successful segment inventory fetch (unreachable, slow, or misconfigured servers).

Common situations: Historicals down or still starting during broker/coordinator startup, network/firewall blocking the inventory HTTP endpoints, wrong druid.host settings, transient network partitions.

Understand the failure class

Background: 'Something went wrong' / 'Request failed (500)' / 'HTTP error! status: 404' — what failed HTTP requests actually mean and how to find the real cause — this error's family across 28 libraries.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/e45b515175b7b5c4. Report an issue: GitHub.

Appendix: source

Thrown at server/src/main/java/org/apache/druid/client/HttpServerInventoryView.java:406

      try {
        Thread.sleep(5000);
      }
      catch (InterruptedException ex) {
        throw new RE(ex, "Interrupted while waiting for queryable server initial successful sync.");
      }

      log.info("Waiting for [%d] servers to sync successfully.", uninitializedServers.size());
      uninitializedServers.removeIf(
          serverHolder -> serverHolder.isSyncedSuccessfullyAtleastOnce()
                          || serverHolder.isStopped()
      );
    }

    if (uninitializedServers.isEmpty()) {
      log.info("All servers have been synced successfully at least once.");
    } else {
      for (DruidServerHolder server : uninitializedServers) {
        log.warn(
            "Server[%s] might not yet be synced successfully. We will continue to retry that in the background.",
            server.druidServer.getName()
        );
      }
    }

    log.info("Invoking segment view initialized callbacks.");
    runSegmentCallbacks(SegmentCallback::segmentViewInitialized);
  }

  private void updateFinalPredicate()
  {
    finalPredicate = Predicates.or(defaultFilter, Predicates.or(segmentPredicates.values()));
  }

  @VisibleForTesting
  void serverAdded(DruidServer server)
  {

View on GitHub (pinned to 9b90983fd2)