Amazon DynamoDB Time to Live (TTL) for .NET Developers - A Complete Guide

Managing data efficiently is crucial for building high-performance and cost-effective .NET applications. Amazon DynamoDB Time to Live (TTL) is a powerful feature that simplifies data lifecycle management by automatically expiring and deleting outdated records from your database. Whether you’re managing session data, cleaning up temporary records, or optimizing storage costs, TTL can significantly enhance your database operations. In this article, we’ll explore how TTL works, why it’s essential for .NET developers, and how to implement it in your applications.

What is Amazon DynamoDB Time to Live (TTL)?

Amazon DynamoDB Time to Live (TTL) is a built-in feature that automatically removes expired items from a DynamoDB table. It enables developers to define an expiration timestamp for individual items, ensuring outdated or irrelevant data is deleted without manual intervention. This helps reduce storage costs, optimize database performance, and streamline data management processes.

TTL isn’t a keyword / feature that is exclusive to DynamoDB, rather it is commonly adapted in systems that need to automatically wipe out temporary data, without you having to run a job that periodically flushes them out.

With TTL in DDB, you designate a specific attribute in your table to store the expiration timestamp in Unix epoch format. Once an item reaches its expiration time, DynamoDB flags it for deletion. The deletion process is handled asynchronously, ensuring minimal impact on table performance.

TTL is especially useful for managing temporary data, such as session tokens, caching records, or logs. It eliminates the need for custom scripts or batch jobs to purge outdated records, making it a reliable and efficient way to manage data lifecycles in applications.

Also, automated deletion using TTL attracts no additional costs.

Why Use TTL in Your .NET DDB Implementations?

Amazon DynamoDB Time to Live (TTL) offers several benefits that make it an essential feature for .NET applications requiring efficient data management. Here’s why you should consider using TTL:

1. Automated Data Expiration

• TTL eliminates the need for manual scripts or background jobs to remove outdated data, saving development time and reducing operational complexity.

2. Cost Optimization

• By automatically deleting expired items, TTL helps reduce storage costs, especially for applications dealing with high data volumes or temporary records.

3. Improved Performance

• Keeping your database free from stale or unnecessary data ensures faster query execution and better overall performance.

4. Simplified Lifecycle Management

• TTL is ideal for handling scenarios like expiring session tokens, cleaning up temporary files, or removing old log entries in a hassle-free way.

5. Ease of Integration

• TTL integrates seamlessly with .NET applications, enabling developers to set expiration attributes programmatically, making it a powerful yet simple tool for efficient database management.

Common Use Cases for DynamoDB TTL

Amazon DynamoDB Time to Live (TTL) is highly versatile and suits various data management scenarios. Here are some common use cases where TTL proves invaluable:

1. Session Management

• Automatically expire user sessions, authentication tokens, or temporary access credentials after a specified time, enhancing security and reducing manual cleanup.

2. Cache Expiration

• Use TTL to remove stale or outdated cache entries from your database, ensuring users always receive the most up-to-date data.

3. Log and Event Cleanup

• Efficiently manage large volumes of logs, audit trails, or event data by setting expiration times to retain only relevant information.

4. Temporary Data Storage

• Handle short-lived data, such as one-time passcodes (OTPs), temporary user preferences, or ephemeral messages, without needing extra purging scripts.

5. Data Retention Policies

• Enforce compliance with data retention policies by automatically deleting records after their mandated lifecycle ends.

6. Shopping Cart Abandonment

• Remove inactive or abandoned shopping cart data after a predefined period to optimize database usage.

By leveraging TTL, .NET developers can automate these tasks, improve efficiency, and maintain cleaner, more cost-effective databases.

How It Works?

You can enable Time to Live (TTL) on any DynamoDB table to automatically manage the lifecycle of your data. Here’s a step-by-step breakdown of how to set it up and make DynamoDB respect TTL:

1. Enable TTL on the Table:

• Start by enabling TTL on the desired DynamoDB table. In the AWS Management Console, under the Time to Live section, specify the attribute that will hold the expiration timestamp for each item. This attribute will store a Unix epoch timestamp (in seconds) representing when the item should expire.

2. Create and Configure the TTL Attribute:

• You need to designate a specific attribute in your table (e.g., ttl) for storing the TTL value. This attribute should hold a timestamp in Unix epoch format (i.e., the number of seconds since January 1, 1970). DynamoDB will use this attribute to determine when to expire and delete the item.

3. Add Expiration Timestamp on Item Creation:

• When your application creates or updates a record in the DynamoDB table, include the expiration timestamp in the TTL attribute. This timestamp should represent the future point in time when the item will expire. For example, if you want an item to expire in 24 hours, you would add an expiration timestamp corresponding to that 24-hour mark (e.g., current time + 24 hours in seconds).

4. Automatic Expiration Process:

• Once you’ve configured TTL and set the expiration time for records, DynamoDB will automatically check the TTL attribute against the current time. If the timestamp has passed, DynamoDB will mark the item as expired. The expiration process is handled asynchronously and does not block your application’s operations.

5. Preview TTL Mode (Optional):

• In the Preview TTL mode, expired items are not deleted immediately but are flagged as expired. This allows you to test and monitor the TTL functionality without actually removing items from the table. You can inspect expired items to verify that the TTL logic is working as expected.

6. Automatic Deletion:

• After TTL is fully enabled, DynamoDB automatically deletes expired items during its background cleanup process. The deletion happens with minimal impact on performance, as it’s managed internally by DynamoDB. Deleted items are removed permanently and cannot be recovered.

Technical Considerations:

• Granularity: The TTL attribute is checked once every 24 hours by DynamoDB, meaning the deletion of expired items might not be immediate but will happen within that time frame.
• Data Type: The TTL attribute must be of type Number and store the expiration time in Unix epoch format (seconds).
• Consistent Read Behavior: Items marked as expired are not immediately deleted; they can still be read until DynamoDB removes them. Expired items are only eventually deleted.
• Cost: Enabling TTL does not incur any additional costs, but if your table experiences significant data churn, the deletion process can help reduce storage costs over time.

With TTL, you can easily manage time-sensitive data, such as session tokens, logs, or cached data, and ensure that records are automatically cleaned up after they are no longer needed, reducing the need for manual data management.

Configuring Amazon DynamoDB TTL

There are numerous ways to configure Time To Live (TTL) for your Amazon DynamoDB table.

Using AWS Management Console

AWS Management Console is the easiest way to configure your TTL. Open up the Table in DynamoDB, and go to Additional Settings. Here, scroll down till you see Time to Live (TTL). Give an appropriate attribute name, and click on Turn on.

Using CLI

You can also run the following command on your CLI to configure DDB TTL.

aws dynamodb update-time-to-live --table-name audits --time-to-live-specification "Enabled=true, AttributeName=ttl"

Setting TTL via .NET

For this demonstration, I am going to re-use the domain models I created for my previous article. Here we will be working on an endpoint that can create Audit logs and push the data to the audits dynamodb table.

app.MapPost("/audits", async (CreateAuditDto auditDto, IDynamoDBContext context) =>
{
    var audit = new Audit(auditDto.ProductId, auditDto.Action);

    // 10 Seconds from now
    var expirationTime = DateTime.Now.AddSeconds(10);
    audit.TTL = ((DateTimeOffset)expirationTime).ToUnixTimeSeconds();

    await context.SaveAsync(audit);
    return Results.Ok();
});

In the above code, I have set the TTL to 10 seconds, which means that the record will be eligible for deletion within 10 seconds of creation. Ideally, this would be for a few days. But for demonstration purposes I have set it to 10 seconds.

I ran the WebAPI, and posted some random data to the /audits endpoint.

As you can see, the ttl field is now set for the newly created record.

Preview Time to Live

Amazon DynamoDB has this cool Previw TTL feature, which can let you know the records that are eligible for deletion for a defined EPOCH timestamp.

Points to remember about TTL Attribute

• TTL Deletion happens automatically.
• This does not incur any additional costs.
• TTL can take longer than the set expiration. Design your application to be fail safe without relying on this completely.
• TTL should be in UNIX EPOCH format.
• Enabling TTL can take upto a few hours for a new table. But most of the time, it should be enabled in a couple of minutes. Larger tables might take some time depending on the partition / item count.
• DDB usually deletes the expired records in a couple of days, depending on the size of the table. For me it took under an hour to delete the expired data.
• Be careful while querying data from TTL enabled tables. You might have to add query filters that can exclude already expired records, so that it’s TTL value isn’t altered using the new operation. Use TTL wisely.

Conclusion

Amazon DynamoDB’s Time to Live (TTL) feature is a valuable tool for .NET developers looking to efficiently manage data lifecycle, optimize storage costs, and improve performance. By automatically expiring and deleting outdated records, TTL reduces the need for manual intervention and ensures that your database remains clean and efficient. Whether you are managing session data, logs, or temporary records, TTL provides a hassle-free way to automate data cleanup, saving time and resources.

As you integrate TTL into your .NET applications, remember to carefully configure the TTL attribute and ensure that it aligns with your data retention policies. While TTL’s background deletion process is efficient, it’s important to account for the eventual deletion timing and avoid relying solely on TTL for real-time data management. By using TTL effectively, you can streamline your data handling and focus on building high-performance, cost-effective applications.

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