Time Travel retention periods in Snowflake - Step-by-Step Execution

Process Flow - Time Travel retention periods

Set Retention Period

↓

Data Changes Occur

↓

Time Travel Window Active?

No→Data Older Than Retention Removed

Yes↓

Query Historical Data Within Window

↓

Return Data Snapshot

This flow shows how Snowflake keeps data snapshots for a set retention period, allowing queries on past data within that window.

Execution Sample

Snowflake

ALTER TABLE my_table SET DATA_RETENTION_TIME_IN_DAYS = 3;
-- Insert data
INSERT INTO my_table VALUES (1, 'A');
-- Update data
UPDATE my_table SET col2 = 'B' WHERE col1 = 1;
-- Query historical data
SELECT * FROM my_table AT (OFFSET => -1);

This code sets a 3-day retention, modifies data, and queries the previous version using Time Travel.

Process Table

Step	Action	Retention Period (days)	Data State	Query Result
1	Set retention period	3	No data	No output
2	Insert row (1, 'A')	3	Row inserted	Row (1, 'A') visible
3	Update row col2='B'	3	Row updated to (1, 'B')	Current row (1, 'B') visible
4	Query at offset -1 (before update)	3	Row updated	Row (1, 'A') returned
5	Wait 4 days (exceed retention)	3	Data older than 3 days removed	Historical query fails or returns current data

💡 After 3 days, historical data older than retention period is removed, so Time Travel cannot access it.

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 5
DATA_RETENTION_TIME_IN_DAYS	1 (default)	3	3	3
DATA_STATE	Empty	Row (1, 'A')	Row (1, 'B')	Row (1, 'B')
HISTORICAL_DATA_AVAILABLE	No	Yes (1 day old)	Yes (updated)	No (older than 3 days)

Key Moments - 3 Insights

Why can't we query data older than the retention period?

Because Snowflake removes historical data beyond the retention period, as shown in step 5 of the execution_table where data older than 3 days is deleted.

Does updating data reset the retention period?

No, the retention period is fixed when set. Updates create new versions but do not extend retention, as seen in steps 3 and 4.

What happens if we query historical data within the retention period?

Snowflake returns the data snapshot from that time, demonstrated in step 4 where querying at offset -1 returns the previous row version.

Visual Quiz - 3 Questions

Look at the execution_table, what is the data state after step 3?

A Row (1, 'A')

B Row (1, 'B')

C No data

D Historical data removed

💡 Hint

Check the 'Data State' column for step 3 in the execution_table.

At which step does historical data become unavailable due to retention period expiry?

A Step 2

B Step 3

C Step 5

D Step 4

💡 Hint

Look for when data older than retention is removed in the execution_table.

If the retention period was set to 1 day instead of 3, how would step 4's query result change?

A It would fail or return current data if more than 1 day passed

B It would still return the previous version

C It would return no data at all

D It would return data from 3 days ago

💡 Hint

Refer to the 'Retention Period' and 'Query Result' columns in the execution_table.

Concept Snapshot

Snowflake Time Travel lets you query past data versions.
Set retention period (default 1 day, max 90 days).
Data changes are kept for that period.
Queries with AT or OFFSET access snapshots.
After retention, old data is removed and inaccessible.

Full Transcript

This visual execution shows how Snowflake's Time Travel retention period controls how long historical data is kept. First, you set the retention period, for example 3 days. When data is inserted or updated, Snowflake keeps snapshots for that time. You can query previous versions within the retention window using special syntax. After the retention period passes, Snowflake removes old data snapshots, so querying older data fails or returns current data. The execution table traces each step: setting retention, inserting data, updating data, querying historical data, and data removal after retention expires. Variables track retention days, data state, and availability of historical data. Key moments clarify why data older than retention is unavailable, that updates don't reset retention, and how queries return snapshots within the window. The quiz tests understanding of data state changes, when data becomes unavailable, and effects of changing retention period. The snapshot summarizes the core idea: Time Travel keeps data snapshots for a set time, enabling queries on past data until retention expires.

Practice

1. What does the Time Travel retention period in Snowflake control?

easy

A. How long you can access previous versions of data

B. How long data is stored in the cloud

C. The speed of query execution

D. The number of users who can access a table

Solution

1. Step 1: Understand Time Travel feature

   Time Travel allows you to see and restore past versions of your data.

2. Step 2: Identify what retention period controls

   The retention period sets how many days you can access these past versions.

3. Final Answer:

   How long you can access previous versions of data -> Option A

4. Quick Check:

   Retention period = access duration for past data [OK]

Hint: Retention period means how long past data is accessible [OK]

Common Mistakes:

• Confusing retention with storage duration
• Thinking it controls query speed
• Assuming it limits user access

2. Which SQL command correctly sets the Time Travel retention period to 7 days for a table named sales_data?

easy

A. ALTER TABLE sales_data SET RETENTION_DAYS = 7;

B. ALTER TABLE sales_data SET DATA_RETENTION_TIME_IN_DAYS = 7;

C. UPDATE TABLE sales_data SET DATA_RETENTION_TIME_IN_DAYS = 7;

D. ALTER TABLE sales_data DATA_RETENTION = 7;

Solution

1. Step 1: Recall correct syntax for setting retention

   The correct command uses ALTER TABLE with SET DATA_RETENTION_TIME_IN_DAYS.

2. Step 2: Match syntax with options

   ALTER TABLE sales_data SET DATA_RETENTION_TIME_IN_DAYS = 7; matches the exact syntax; others use incorrect keywords or commands.

3. Final Answer:

   ALTER TABLE sales_data SET DATA_RETENTION_TIME_IN_DAYS = 7; -> Option B

4. Quick Check:

   Use ALTER TABLE ... SET DATA_RETENTION_TIME_IN_DAYS [OK]

Hint: Use ALTER TABLE ... SET DATA_RETENTION_TIME_IN_DAYS [OK]

Common Mistakes:

• Using UPDATE instead of ALTER TABLE
• Wrong keyword like RETENTION_DAYS
• Missing SET keyword

3. Given a table with a Time Travel retention period of 3 days, what happens if you try to query data from 5 days ago using Time Travel?

medium

A. You get an error because data older than 3 days is not available

B. You get the data from 5 days ago without issues

C. The query runs but returns empty results

D. The retention period automatically extends to 5 days

Solution

1. Step 1: Understand retention period limit

   Retention period limits how far back you can access data versions.

2. Step 2: Apply to 5 days query with 3 days retention

   Since 5 days is beyond 3 days retention, data is unavailable and causes an error.

3. Final Answer:

   You get an error because data older than 3 days is not available -> Option A

4. Quick Check:

   Query beyond retention period = error [OK]

Hint: Cannot access data older than retention days [OK]

Common Mistakes:

• Assuming data is always available
• Thinking query returns empty instead of error
• Believing retention auto-extends

4. You tried to set the Time Travel retention period to 100 days on a table, but Snowflake returned an error. What is the most likely cause?

medium

A. You need to restart the Snowflake service

B. Syntax error in the ALTER TABLE command

C. Table does not support Time Travel

D. Retention period exceeds the maximum allowed limit

Solution

1. Step 1: Know Snowflake retention limits

   Snowflake limits Time Travel retention to a maximum (usually 1 to 90 days depending on edition).

2. Step 2: Check if 100 days exceeds limit

   100 days is beyond typical max, causing an error.

3. Final Answer:

   Retention period exceeds the maximum allowed limit -> Option D

4. Quick Check:

   Retention > max limit causes error [OK]

Hint: Check max retention days allowed before setting [OK]

Common Mistakes:

• Assuming syntax error without checking limits
• Thinking table lacks Time Travel support
• Believing service restart fixes retention errors

5. A company wants to keep Time Travel data for 14 days but minimize storage costs. Which approach best balances these needs?

hard

A. Set DATA_RETENTION_TIME_IN_DAYS to 30 to avoid data loss

B. Set DATA_RETENTION_TIME_IN_DAYS to 1 and rely on backups for older data

C. Set DATA_RETENTION_TIME_IN_DAYS to 14 and regularly purge old data

D. Disable Time Travel and keep manual snapshots

Solution

1. Step 1: Understand retention vs storage cost

   Longer retention means more storage cost; shorter retention saves cost but limits recovery.

2. Step 2: Evaluate options for 14-day retention and cost balance

   Setting retention to 14 days meets recovery needs; purging old data helps control storage.

3. Final Answer:

   Set DATA_RETENTION_TIME_IN_DAYS to 14 and regularly purge old data -> Option C

4. Quick Check:

   Retention matches need + purge controls cost [OK]

Hint: Match retention days to need, purge to save cost [OK]

Common Mistakes:

• Setting retention too low losing data
• Setting retention too high increasing cost
• Disabling Time Travel losing recovery benefits