Today while working on a ror project we run into an abrupt issue wiht transaction where even if the transaction was not being processed the id was increasing leading to a failure in a backgroud sidekiq worker this lead me to this stackover flow post

Post Which then led me in rabit hole that i have tried to pen to the best of my abilities below :->

PostgreSQL Sequences: Unexpected Increments?

Imagine you’re working with a PostgreSQL database, and you’ve set up a sequence to auto-increment primary keys for your Client model. Everything seems fine until you encounter a puzzling issue: the sequence value jumps up even when a client creation fails.

The Mystery Unveiled

In PostgreSQL, sequences are special objects used to generate unique identifiers, commonly for primary key fields. When you create a new record, PostgreSQL automatically fetches the next value from the sequence and assigns it to the primary key column.

Example Scenario

Let’s say your sequence currently stands at 262. You attempt to create a new client, but due to a unique constraint violation (perhaps someone manually set a primary key, which PostgreSQL sequences ignore), the creation fails. Oddly enough, upon rechecking the sequence, you find it’s incremented to 263, despite no new client being added to the database.

Why Does This Happen?

PostgreSQL’s sequence mechanism operates independently of transaction rollbacks. When you call nextval on a sequence (implicitly done when a new record is inserted), it advances the sequence whether or not the transaction succeeds or fails. This design ensures each session receives a unique sequence value, even if multiple sessions are running concurrently.

Consider the Consequences

This behavior can lead to unexpected scenarios if not handled carefully. For instance, if your application logic relies on sequential numbering for auditing or reporting purposes, gaps might appear if transactions fail after fetching a sequence value. These gaps are harmless but can be surprising if not anticipated.

Best Practices

To avoid issues:

• Avoid Manually Setting Primary Keys: Let PostgreSQL manage sequence values automatically.
• Handle Unique Constraints Gracefully: Ensure your application handles unique constraint violations gracefully to prevent unnecessary gaps in sequence usage.

Visualizing PostgreSQL Sequence Behavior

To illustrate, here’s a table summarizing how PostgreSQL sequences behave:

Conclusion

Understanding PostgreSQL sequences is crucial for maintaining data integrity and application reliability. While the behavior of sequence incrementation on failed transactions might seem counterintuitive at first, it ensures robustness and scalability in multi-session environments.

So, the next time you encounter an unexpected sequence increment in PostgreSQL, remember: it’s all part of PostgreSQL’s design to maintain transactional integrity and support concurrent operations seamlessly.

By grasping these nuances, you can navigate PostgreSQL’s sequence behavior more effectively, ensuring your applications perform reliably even under challenging conditions. Understanding these mechanics not only enhances your troubleshooting skills but also empowers you to design more resilient database architectures.