Outcome
By the end of this lesson, you will be able to explain what a managed database is and name the separate meters it runs on.
| Prerequisites | L1, L2 |
| Time | 8 minutes |
1. Concept
A database is an organised store of records that software can search and update quickly. Customer accounts, orders, stock levels: the facts an application needs to look up in a fraction of a second.
You could run a database yourself on a VM. You would install the software, take backups, apply security fixes and repair it when it breaks. Most teams prefer to rent a managed database instead: the provider runs the database software for you and handles backups, updates and recovery. It is like renting a flat with a building manager, rather than a bare room.
Two kinds you will meet
1. Instance-based databases. You choose a size, just like a VM, and the database runs on it all the time.
- AWS calls its main one RDS.
- Google Cloud calls it Cloud SQL.
- Azure offers Azure SQL Database and others.
2. Pay-per-request databases. There is no machine size to choose. You pay for each read and write, plus the data stored.
- AWS: DynamoDB.
- Google Cloud: Firestore.
- Azure: Cosmos DB.
(Several of these services also offer other pricing options. The split above is the simplest way to start.)
What the meters count
A managed database is not one charge. It is several of the meters you already know, bundled under one name.
For an instance-based database:
- Time, for the instance (the machine underneath), per hour it is running. Like a VM, it charges whether it is busy or idle.
- Storage, per GB-month for the space allocated to the data.
- Backups, per GB-month for copies kept beyond any free allowance.
- Often a standby copy in another zone, kept ready in case the main one fails. This roughly doubles the instance charge.
For a pay-per-request database:
- Requests, a tiny amount per read or write.
- Storage, per GB-month.
This means a database is usually one of the larger single items on a bill, because it combines compute and storage, often runs all the time and is often doubled for safety.
2. Worked example
One instance-based database for one month. Prices are illustrative.
| Item | Amount | Illustrative rate | Monthly cost |
|---|---|---|---|
| Database instance, on all month | 730 hours | $0.20 per hour | $146 |
| Standby copy in a second zone | 730 hours | $0.20 per hour | $146 |
| Storage allocated | 200 GB | $0.12 per GB-month | $24 |
| Extra backup storage | 100 GB | $0.10 per GB-month | $10 |
| Total | $326 |
The team thinks of this as “the database”. On the bill it shows up as four separate lines. The standby copy alone costs as much as the main database. That is often the right choice for a live customer system, and rarely needed for a test copy.
3. Hands-on (5 min: no account needed)
1. Open the Azure Pricing Calculator: azure.microsoft.com/pricing/calculator2. Search for and add "Azure SQL Database".3. Pick any region and a small size. Note the monthly estimate.4. Look at the storage and backup options in the same form and note that each has its own price.5. If the form offers a "zone redundant" or high-availability option, switch it on and note how the estimate changes.You should see a single “database” broken into several priced parts. The AWS Pricing Calculator (calculator.aws, add “Amazon RDS”) and the Google Cloud Pricing Calculator (add “Cloud SQL”) show the same pattern.
4. Knowledge check
Q1
What does “managed database” mean?
A. A database that only managers in the company are allowed to read
B. A database the provider runs for you, including backups and updates
C. A database stored on paper as a backup for the digital one
D. A database that is always free for small amounts of data
Show answer
Correct: B. “Managed” means the provider operates the database software, so your team does not have to patch, back up and repair it. It says nothing about who can read it, and it is not free.
Q2
An instance-based database sits almost unused overnight. What happens to its instance charge?
A. It stops until the next request arrives
B. It drops to the storage charge only
C. It switches to a per-request price automatically
D. It keeps charging per hour, the same as when busy
Show answer
Correct: D. The instance underneath is charged per hour it runs, like a VM, regardless of how busy it is. Only pay-per-request databases charge by activity.
Q3
Why does a database often show up as several lines on a bill?
A. It combines instance time, storage, backups and sometimes a standby copy
B. The provider splits the price to hide the real total from customers
C. Each person who uses the database gets a separate line
D. Every table inside the database is billed as its own item
Show answer
Correct: A. A managed database bundles several meters you already know: time, storage and backups, plus a standby copy if you choose one. The lines are not per user or per table.
5. Apply
When someone says “the database costs too much”, ask which part. The instance size? The standby copy? Storage that was allocated generously and never filled? Backups kept for years? Each has its own line and its own fix, and the answer is usually one of them, not all four.