> ## Documentation Index
> Fetch the complete documentation index at: https://docs.smcps.net/llms.txt
> Use this file to discover all available pages before exploring further.

# Queue Management

> Redis-backed query queue for concurrent execution control per connection

SMKRV MCP Studio uses a Redis-backed queue to control concurrent query execution per database connection. This prevents overwhelming databases with too many simultaneous queries.

## Overview

When an MCP client calls a tool that executes a SQL query:

1. The tool requests a query slot for its bound connection
2. If a slot is available (under `max_concurrent_queries`), the query executes immediately
3. If all slots are taken, the query is placed in a FIFO queue
4. When a running query completes, the next queued query is released
5. If a queued query waits longer than `queue_timeout_seconds`, it is rejected

## Per-Connection Settings

Configure queue settings in the connection editor: go to **Connections**, open a connection, and scroll to the **Queue** section. Each connection has independent settings:

| Setting                  | Range   | Default | Description                            |
| ------------------------ | ------- | ------- | -------------------------------------- |
| `max_concurrent_queries` | 1-200   | 5       | Maximum queries running simultaneously |
| `queue_timeout_seconds`  | 1-300   | 30      | Maximum wait time in the queue         |
| `queue_enabled`          | boolean | true    | Whether queueing is active             |

### Choosing Values

* **Small databases or shared hosts**: Keep `max_concurrent_queries` low (2-5)
* **Dedicated database servers**: Increase to 20-50 depending on capacity
* **Long-running analytical queries**: Increase `queue_timeout_seconds` to 120-300
* **Quick OLTP queries**: Keep timeout at 10-30 seconds

## Queue Monitor

The **Queue Monitor** tab on the Server page displays real-time metrics:

| Metric         | Description                                          |
| -------------- | ---------------------------------------------------- |
| Active Queries | Number of queries currently executing per connection |
| Queued Queries | Number of queries waiting in the queue               |
| Total Executed | Cumulative query count per connection                |

## Fallback Behavior

When Redis is unavailable, MCP Studio falls back to in-memory concurrency control:

| Feature             | Redis Mode        | Fallback Mode    |
| ------------------- | ----------------- | ---------------- |
| Concurrency control | Distributed       | Per-process only |
| Queue persistence   | Survives restarts | Lost on restart  |
| Metrics             | Full              | Limited          |

## Troubleshooting

### Queries Timing Out in Queue

* Increase `queue_timeout_seconds`
* Increase `max_concurrent_queries` if the database can handle more load
* Check for long-running queries holding slots

### Redis Connection Failed

5-container docker-compose setup:

```bash theme={null}
docker compose ps redis
docker compose logs redis
docker compose exec redis redis-cli -a "${REDIS_PASSWORD}" ping
```

All-in-one Docker Hub image:

```bash theme={null}
docker exec mcp-studio supervisorctl status redis
docker logs mcp-studio
docker exec mcp-studio redis-cli -a "${REDIS_PASSWORD}" ping
```

### Queue Not Limiting Queries

* Verify `queue_enabled` is `true` on the connection
* Confirm Redis is connected (check the indicator on the Server page)

***

## See Also

<CardGroup cols={2}>
  <Card title="Connections" icon="database" href="/user-guide/connections">
    Configure queue settings per connection
  </Card>

  <Card title="Deployment" icon="rocket" href="/user-guide/deployment">
    Deploy the MCP server that uses the query queue
  </Card>

  <Card title="Configuration" icon="gear" href="/configuration">
    Redis and queue environment variables
  </Card>

  <Card title="Troubleshooting" icon="bug" href="/troubleshooting">
    Redis connection issues and debugging tips
  </Card>
</CardGroup>