🟢 What is CDC?
CDC is a feature in databases that records every change—when a row is added, updated, or deleted.
Think of it like a CCTV camera for your database.
Whenever data changes, CDC quietly writes a note about it.
💡 Why is it useful?
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You can send only new changes to another system (like a data warehouse) instead of copying everything.
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You can trigger actions when data changes (e.g., send an email when an order ships).
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It helps with auditing (who changed what and when).
⚙️ How it works (step by step)
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Turn it on
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An admin tells the database: “Watch this table for changes.”
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Database watches the transaction log
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Every insert, update, or delete is already recorded in the database log.
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CDC reads that log.
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Change table created
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CDC puts details of each change into a special table (e.g.,
cdc.Orders_CT). -
This table shows:
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What kind of change happened (insert/update/delete)
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Old and new values
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The time of the change.
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Your app reads the changes
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Your app or ETL job asks: “Give me all changes since last time.”
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It processes those and remembers the last point it read.
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🧠 Simple Example
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You have an Orders table.
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You update order #5’s status to “Shipped.”
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CDC writes a row into its change table:
“Order #5 changed from Pending → Shipped at 10:32 AM.”
✅ Good Things
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No triggers needed: It uses the existing transaction log.
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Fast: Only new changes are read.
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Real-time: You see changes almost immediately.
⚠️ Things to keep in mind
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Change tables can grow big—set cleanup rules.
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Only users with permission should read CDC data.
🏁 Quick Summary
CDC = Automatic change tracker for your database.
It watches every insert, update, or delete and stores those details in a special table, so other apps can easily know exactly what changed without scanning everything.
