CDC vs Snapshot Comparison: Which Should You Use?
Both approaches tell you what changed. They differ in speed, setup and what they can see.
Log-based CDC reads the database's transaction log. It sees every change as it happens, including a row that was updated twice, and it can stream to a warehouse or queue. It needs access to the database, setup and an engineer to run it.
Snapshot comparison takes two copies of the data and finds the differences between them. It needs no access to the source system, only the two files. It sees the net change between the two moments, so a row that was changed and changed back shows nothing, and two updates between snapshots show as one. That is fine for a daily check, an audit or a migration test.
Use log-based CDC when you need near real-time data in another system. Use a snapshot comparison when you only have exports, when you need a one-off answer, or when you want to check that a CDC pipeline or an incremental load did what you expected: compare the source export with the target export and look for rows that are missing or different.
For files, Data Comparison does the snapshot version. Load the two exports, choose the key and read the inserts, updates and deletes. It reads CSV and Excel files, so convert Parquet or JSON to CSV first. Everything runs in your browser and nothing is uploaded.
Related tool pages
- Compare Two CSV Files: Compare two CSV or Excel files by a key column and see added, removed and changed rows. Free, runs in your browser.
- Compare Two Excel Files: Compare two Excel (.xlsx) files by a key column and see every added, removed and changed row and cell. Free, and your files stay in your browser.
- CSV Diff Tool: Find the differences between two CSV files online: which rows were added, removed or changed, cell by cell. Free, in your browser.
- CDC for CSV and Excel Files (Change Data Capture): Change data capture for files: compare two CSV or Excel snapshots and list inserts, updates and deletes by key. Free, private, runs in your browser.
- Detect Changes Between Two CSV Files: Find new, deleted and edited rows between two CSV files, cell by cell, matched by a key column. Free, and your files stay in your browser.
- Find New, Updated and Deleted Rows Between Two Files: List the new, updated and deleted rows between two CSV or Excel files by key and download the differences. Free and private.
How to use the Data Comparison: step by step
- Export the source and the target, or yesterday and today.
- Open Data Comparison and load both.
- Choose the key column.
- Review missing, new and different rows.
When to use the Data Comparison
- Verify that a CDC pipeline loaded everything
- Check a daily extract against the last one
- Test an incremental load
- Audit a migration
Example
Input: before.csv + after.csv, key = id
Output: Added 3 · Removed 2 · Changed 5
Frequently asked questions
Can I use it for change data capture (CDC)?
For files, yes. Load yesterday's snapshot and today's, choose the key, and the added rows are the inserts, the changed rows are the updates and the removed rows are the deletes. It is a snapshot comparison, not log-based CDC: it does not read database logs or stream changes live.
How do I find new, updated and deleted rows between two files?
Load both files, choose a key column such as id, and read the three lists: added (new), changed (updated, with the old and new value of each cell) and removed (deleted).
Can the files be different formats?
Yes. A can be a CSV and B an Excel file. Columns are matched by name. JSON and Parquet files are not supported here, so convert them to CSV first.
Can Data Comparison do change data capture (CDC)?
It does the snapshot version of CDC for files. Compare the earlier and the latest export by key: added rows are inserts, changed rows are updates and removed rows are deletes. It does not read database logs or run in real time.
Tip: To test a pipeline, compare the source export with the target export. Rows that are missing or different point to the problem.