Maximizing Ticket Allocation Efficiency with Redis Sorted Sets
Tags: redis, sortedset, priorityq, ticketingsystem
Published: 2023-06-03 09:20:29

I recently had the opportunity to work on building a ticketing allocation system. In this blog post, I would like to share my experience and discuss how the use of Redis sorted sets can be a valuable approach in achieving efficient ticket allocation.

## The Challenge
Assigning tickets to the right support employees based on various criteria, such as availability, workload, and ticket priorities, can greatly impact customer satisfaction and team efficiency. The goal is to design a system that can handle dynamic ticket allocation and ensure a fair distribution of tickets among employees.

## Sorted Sets to the Rescue
To address this challenge, one can turn to Redis, an in-memory data structure store, and leverage its sorted sets functionality. Sorted sets are a powerful data structure that allows for efficient sorting and retrieval of elements based on a score assigned to each element.

https://redis.io/docs/data-types/sorted-sets/

## Implementation
Here's a detailed overview of how you can utilize sorted sets to build the ticketing allocation system.

#### Storing Employee Availability
Store the availability status of employees using Redis sets.

#### Assigning Scores to Tickets
Determine the priority score of each ticket by devising a scoring mechanism based on various factors such as urgency, impact on customers, and SLA requirements. Customize the formula for calculating the score based on specific business needs. For example, a ticket with high priority and a short SLA might receive a higher score than a low-priority ticket with a longer SLA.

Redis sorted sets offer a powerful solution for sorting tickets based on multiple data points. By assigning float value scores to tickets, combining priority and turnaround time (TAT), sorting becomes efficient. For example, the priority score of 1.0 and TAT score of 0.1324 can be combined as 1.1324.

#### Creating Sorted Sets for Tickets and Employee Queues
You can utilize Redis sorted sets for storing the tickets and maintaining employee queues based on the number of tickets assigned. Each support employee is added in an employee queue (redis sorted set) where the number of tickets assigned serves as the score of each member. This allows for efficient retrieval of employees with the least number of tickets.

#### Allocating Tickets
Tickets can be allocated to employees either in real-time, as soon as the ticket is raised, or periodically. In the case of real-time assignment, tickets are assigned to the employee who has been assigned the least number of tickets, which is a constant time operation (0(1)) in sorted sets as employees are always sorted based on the number of tickets assigned to them.

For tickets that are in queues due to employees being unavailable, they can be assigned to employees based on ticket priority. This ensures that employees with fewer assigned tickets are always assigned first, maintaining a fair distribution of the workload.

#### Updating Scores, Availability, and Employee Queues
As tickets are assigned to employees, you can remove tickets from the sorted sets. Additionally, you can update the employee queues by incrementing the number of tickets assigned to the respective employee in the employee sorted set.

## Understanding Time Complexities

Redis sorted sets offer excellent time complexities that contribute to the efficiency of the ticket allocation system:

- **Adding a ticket to the sorted set**: With Redis, adding a ticket to the sorted set has a time complexity of `O(log N)`, where N is the number of elements in the sorted set. This operation can be achieved using the `ZADD` command, which allows you to add a ticket to the sorted set with its priority score.

- **Fetching a range of tickets based on priority**: Retrieving a range of tickets from the sorted set based on priority has a time complexity of `O(log N + M)`, where N is the number of elements in the sorted set and M is the number of tickets in the requested range. This can be done using the `ZRANGEBYSCORE` command, which returns a range of tickets based on their priority scores. `ZRANGE` can be used to fetch tickets based on their positions in the sorted set.

- **Pushing a ticket to an employee queue (sorted set)**: `O(log N)` This operation can be accomplished using the `ZADD` command, similar to adding a ticket to the main sorted set.

- **Updating employee availability (Redis sets)**: Updating the availability of employees, stored in Redis sets, has a constant time complexity of `O(1)`. You can update the availability status of an employee using the `SADD` or `SREM` commands to add or remove the employee from the availability set.


## Benefits of this Approach

- **Scaling with Increasing Ticket Volume**: As the number of tickets in the system grows into the thousands or millions, Redis sorted sets continue to provide efficient performance for fetching and sorting tickets based on priority. The logarithmic time complexity ensures that the system can handle the increasing volume of tickets without sacrificing responsiveness.

- **Real-Time Ticket Updates**: In a dynamic environment where ticket priorities frequently change, the ticket allocation system powered by Redis allows for real-time updates of ticket scores. This enables immediate adjustments to ticket positions within the sorted set, ensuring that the most critical tickets are always readily accessible for assignment to employees.

- **Concurrent Ticket Assignments**: In scenarios where multiple employees are simultaneously fetching tickets for assignment, Redis sorted sets handle concurrent access gracefully. The built-in atomicity of Redis commands guarantees that each employee retrieves a consistent and accurate range of tickets based on priority, without conflicts or interference.

- **Efficient Load Distribution**: With the ability to assign tickets based on priority scores, Redis sorted sets ensure an equitable distribution of workload among available employees. Critical tickets are promptly allocated to the most appropriate employees, preventing any single employee from being overwhelmed. This load distribution mechanism optimizes team productivity and enhances customer satisfaction.

- **High-Speed Ticket Retrieval**: Redis excels at delivering lightning-fast response times, even as the number of tickets and employees increases. The efficient time complexities of Redis sorted sets enable sub-millisecond retrieval of tickets based on priority, allowing for rapid allocation decisions and minimizing any potential delays in ticket handling.


## Conclusion
Utilizing Redis sorted sets for both ticket storage and employee queues offers a powerful and efficient approach to building a ticketing allocation system. The combination of fast retrieval, fair workload distribution, real-time updates, and scalability makes this implementation highly effective in managing and assigning tickets based on priority and employee availability.