Why Do MongoDB Documents with TTL Set to Expire in Go Not Always Delete Immediately?

MongoDB in Go: Automating Document Expiration after a Specified Duration

In MongoDB, documents can be automatically deleted after a specified number of seconds. This feature, known as Time to Live (TTL), is particularly useful for managing ephemeral data that should not be retained for an extended period.

Problem:

Implementing TTL in Go requires creating an index with the expireAfterSeconds option. However, users may encounter situations where inserted documents do not expire as expected.

Example Code and Issue:

<code class="go">// Sample code to set TTL index and insert documents
// May not always expire documents immediately</code>

In the example above, a TTL index is created for the "createdAt" field, setting it to expire documents after 1 second. However, it is possible that inserted documents remain persistent even beyond this specified duration.

Solution:

The potential delay in document expiration results from the asynchronous nature of MongoDB's TTL implementation. The TTL process runs as a background task that periodically scans for expired documents and removes them. This task runs every 60 seconds. Therefore, a document may remain present in the collection for up to 60 seconds after expiring. Additionally, under heavy database workloads, the removal operation may take longer.

Implications:

This behavior is intended to prevent performance degradation caused by continuous document deletion. It is important to consider these timing aspects when using TTL in applications. If immediate deletion is required, alternative mechanisms should be explored.

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