New to a Large Project? This Is How I Decode Complex Databases

When you join a large-scale project:

• Multiple microservices
• Each service has its own database
• Each database has dozens of tables
• Each table has millions of rows

As a new developer or QA, the biggest struggle is:

"Where is the data coming from and how are things connected?"

Asking others every time slows you down and reduces confidence. So here is a step-by-step approach I use to understand the database on my own.

Step 1: Start From the Business Flow (Not Tables)

Ask yourself what is the core business flow? (order, payment, user, inventory, etc.)
Example:

• Order Service → order, order_items
• Payment Service → payments, transactions
• User Service → users, addresses

👉 This prevents random table jumping.

Step 2: Identify the "Anchor Table"

In every service, there is one main table.
Examples:

• orders
• users
• payments

This table usually:

Has id, status, created_at

DESC orders;
SELECT * FROM orders LIMIT 10;

Step 3: Use Naming Conventions to Detect Relationships

In microservice-based Database:

• Foreign keys are often not enforced
• Relationships are logical, not physical

Look for:

• order_id
• user_id
• payment_id

Example:


SELECT * FROM order_items WHERE order_id = ?;

👉 Column names tell the story even without FK constraints.

Step 4: Track Data Using Real IDs (Reverse Engineering)

Pick one real record and follow it everywhere.
Example flow:

• Get one order_id
  Search it in:

• payments

• order_items

• shipment

• audit tables

SELECT * FROM payments WHERE order_id = 123;

👉 This builds mental mapping very fast.

Step 5: Understand Status Columns Deeply

Status columns are more important than relationships.

SELECT DISTINCT status FROM orders;

👉 This explains 80% of production bugs.

Step 6: Read Application Code Just for Repositories/DAOs

You don't need full code understanding.
Just search for: Repository, SQL queries, JPA entities

Step 7: Draw Your Own Simple Diagram Or Maintain Notes

No fancy tools needed.
Just draw:
Table names
Arrows using *_id
Status flow

Also maintain a notes, create a small doc:
Table name, Purpose, Important columns

Even a rough diagram and notes gives huge clarity.

Large MySQL databases in microservice systems look scary at first.
But they are just well-organized business flows stored in tables.
Hope this will help you nd add some value in your life, follow for more😊