FileStore 'no idx present' warning spam under high WorkQueue throughput

[styler]

Observed behavior

Under high-throughput WorkQueue workloads with frequent message acknowledgements, the filestore enters a state where it continuously logs warnings:

Cache lookup detected no cache: no idx present

This causes:

• Massive warning spam in logs
• High CPU usage
• High disk usage

The issue only resolves after server restart. No memory pressure observed.

Expected behavior

The server should handle high-throughput WorkQueue workloads without entering a degraded state that requires restart to recover.

Server and client version

nats-server v2.12.2

Host environment

Linux, observed in Kubernetes pods

Steps to reproduce

1. Create a stream with WorkQueue retention policy
2. Produce messages at high throughput
3. Consume and acknowledge messages at high rate
4. After running for some time, observe the warning spam begins

[neilalexander]

Can you please provide the stream info?

[styler]

For sure

                Subjects: viewer-deployment-revenue-daily-queue.>
                Replicas: 3
                 Storage: File
       Placement Cluster: core

Options:

               Retention: WorkQueue
         Acknowledgments: true
          Discard Policy: Old
        Duplicate Window: 2m0s
              Direct Get: true
    Allows Batch Publish: false
         Allows Counters: false
       Allows Msg Delete: true
  Allows Per-Message TTL: false
            Allows Purge: true
        Allows Schedules: false
          Allows Rollups: false

Limits:

        Maximum Messages: unlimited
     Maximum Per Subject: unlimited
           Maximum Bytes: unlimited
             Maximum Age: unlimited
    Maximum Message Size: unlimited
       Maximum Consumers: unlimited

Cluster Information:

                    Name: core
           Cluster Group: S-R3F-i8vXZMbL
                  Leader: core-nats-0 (19h54m20s)
                 Replica: core-nats-1, current, seen 34ms ago
                 Replica: core-nats-2, current, seen 34ms ago

State:

            Host Version: 2.12.2
      Required API Level: 0 hosted at level 2
                Messages: 76,481
                   Bytes: 24 MiB
          First Sequence: 52,524,393 @ 2025-12-09 02:32:17
           Last Sequence: 52,611,882 @ 2025-12-09 10:12:00
        Deleted Messages: 11,009
        Active Consumers: 1
      Number of Subjects: 1