RDS with multiAz enabled not deleting automated backups according to backup retention
Problem
My RDS instance's automated backups are not deleting after 1 day (the configured backup retention period). In my account I see 3 automated backups for the database. one backup for each of the past 3 days.
What I expected
My RDS instance to only have 1 automated backup at any given time. Because I've specified backup retention of 1 day it should delete the previous days backup right after creating a new backup.
My instance
- MultiAZ: enabled
- Engine: Postgres 14.3
- Backup Retention: 1 day
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Hi, It is expected for PITR requirements. Please see below explanation from RDS FAQs page.
https://aws.amazon.com/rds/faqs/ Q. Why do I have more automated DB snapshots than the number of days in the retention period for my DB instance?
A. It is normal to have 1 or 2 more automated DB snapshots than the number of days in your retention period. One extra automated snapshot is retained to ensure the ability to perform a point in time restore to any time during the retention period. For example, if your backup window is set to 1 day, you will require 2 automated snapshots to support restores to any within previous 24 hours. You may also see an additional automated snapshot as a new automated snapshot is always created before the oldest automated snapshot is deleted.
I just learned it can be far worse, than this.
In my case there 11 (Sic!) backups retained while the retention was set to 1 day.....
This happened since the machine concerned was an Acceptance machine that is often running for a few hours a day only (elastic!). Unfortunately the DB concerned was 800GB, which made these copies rather expensive!
Since then I learned that the 1 day retention period is actually a 24 hour retention where only the 'running' state hours are calculated........
As stated in the documentation [1], Backups can be retained longer than the backup retention period if a database has been stopped. RDS doesn't include time spent in the stopped state when the backup retention window is calculated.
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Thank you for the explanation and link. Do you know if we're charged for these extra backups?