Compare the structure of two snapshots

Comparing structure shows what changed in a table between two snapshots, such as added columns, a new partitioning, or a jump in the record count. It does not read the rows, so it is fast and a good first check before you compare data.

Prerequisites

• Your role includes time_machine:metadata_diff. The portal_admin, data_engineer, and data_analyst roles have it.
• You can read the table in Data Security.
• The table has at least 2 snapshots.

Choose the order of the snapshots

You pick two snapshots: Snapshot A and Snapshot B. Time Machine treats A as "before" and B as "after", and calculates every change as B minus A. It does not sort them by time for you.

Pick the older snapshot as A and the newer one as B. If you swap them, the numbers are still right, but they read backwards. A table that grew by 500 records shows as -500.

Compare the structure

1. Open the Time Machine tab of the table.
2. Select the older snapshot in Snapshot A.
3. Select the newer snapshot in Snapshot B. It must be different from A.
4. Select Compare.

Read the result

The result has six sections.

Section	What it compares
Snapshot	The two snapshots: ID, time, and kind of write.
Schema	Columns added, removed, or changed in type.
Partition	How the table is split into partitions.
Properties	The technical settings of the table.
Files	The number and size of data files.
Records	The number of records, and the change from A to B.

A section can show Not available with a reason. For example, the partition layout of an old snapshot may no longer be stored. This is not an error. The other sections are still correct.

If something goes wrong

Situation	What it means	What to do
The snapshot pair is not valid	You picked the same snapshot twice, or one of them does not exist.	Pick two different snapshots from the timeline.
Access denied	Your role or your data access does not allow it.	Ask your administrator for time_machine:metadata_diff or for access to the table.

Next steps

• Compare the data of two snapshots.