Query result reuse is a powerful performance optimization feature in Snowflake that automatically caches the results of executed queries. When an identical query is submitted, Snowflake can return the cached results instead of re-executing the query, significantly reducing compute costs and improvi…Query result reuse is a powerful performance optimization feature in Snowflake that automatically caches the results of executed queries. When an identical query is submitted, Snowflake can return the cached results instead of re-executing the query, significantly reducing compute costs and improving response times.
How It Works:
When a query is executed, Snowflake stores the result set in a persisted query result cache for 24 hours. If the same query is run again within this period, and certain conditions are met, Snowflake retrieves the cached results rather than processing the data again. This happens at no additional cost since no virtual warehouse resources are consumed.
Conditions for Result Reuse:
1. The query text must be exactly identical (including whitespace and case)
2. The underlying table data must not have changed (no DML operations)
3. The same role must be used
4. Micro-partitions accessed by the query must not have changed
5. Any functions in the query must be deterministic
6. The result cache must not have expired (24-hour limit)
Benefits:
- Reduced compute costs since warehouses do not need to spin up
- Faster query response times (sub-second in many cases)
- Improved user experience for repeated analytical queries
- No additional configuration required as it is enabled by default
Considerations:
Queries using non-deterministic functions like CURRENT_TIMESTAMP() or RANDOM() will not benefit from result reuse. Additionally, if underlying data changes frequently, cached results may become invalid quickly.
Management:
Result reuse is enabled by default at the account level. You can disable it at the session level using ALTER SESSION SET USE_CACHED_RESULT = FALSE if needed for testing or specific use cases.
This feature is particularly valuable for dashboards and reports where users frequently run similar queries, providing substantial cost savings and performance improvements in production environments.
Query Result Reuse in Snowflake
Why Query Result Reuse is Important
Query result reuse is a fundamental performance optimization feature in Snowflake that significantly reduces costs and improves query response times. When enabled, Snowflake can return results from previously executed queries in milliseconds rather than re-executing the entire query, saving both compute resources and time.
What is Query Result Reuse?
Query result reuse is a caching mechanism where Snowflake stores the results of queries for a period of 24 hours. When an identical query is submitted, Snowflake retrieves the cached results instead of re-running the query against the data. This feature is enabled by default and works automatically.
How Query Result Reuse Works
When a query is executed in Snowflake:
1. Snowflake first checks if an identical query has been run in the past 24 hours 2. If a match is found and the underlying data has not changed, the cached result is returned 3. No virtual warehouse is required to return cached results, meaning no compute costs are incurred 4. Results are returned almost instantaneously
Conditions for Query Result Reuse
For query results to be reused, several conditions must be met:
• The query text must be exactly the same (including whitespace and capitalization) • The underlying table data must not have changed (no DML operations) • The query must not include functions that return different results each time (like CURRENT_TIMESTAMP() or RANDOM()) • The result cache must not have expired (24-hour limit) • The user must have the necessary privileges on the underlying objects • Micro-partitions accessed by the query must not have changed
Key Features
• No warehouse required: Cached results are returned even if the warehouse is suspended • Cross-user sharing: Results can be shared across users who have access to the same data • Automatic: No configuration needed; it works by default • Cost-effective: Eliminates compute costs for repeated queries
Controlling Query Result Reuse
You can disable result caching at the session or account level using:
ALTER SESSION SET USE_CACHED_RESULT = FALSE;
Or at the account level:
ALTER ACCOUNT SET USE_CACHED_RESULT = FALSE;
Exam Tips: Answering Questions on Query Result Reuse
1. Remember the 24-hour cache duration - This is a commonly tested fact. Results are cached for exactly 24 hours.
2. Know that no warehouse is needed - A key benefit is that cached results can be returned even when the warehouse is suspended, resulting in zero compute costs.
3. Understand invalidation triggers - Any DML operation (INSERT, UPDATE, DELETE, MERGE) on underlying tables invalidates the cache for queries referencing those tables.
4. Be aware of non-deterministic functions - Queries using functions like CURRENT_DATE(), CURRENT_TIMESTAMP(), RANDOM(), or UUID_STRING() cannot leverage result caching because they produce different results each execution.
5. Query text matching is exact - Even minor differences in whitespace or case sensitivity will prevent cache hits.
6. Distinguish from other caching layers - Snowflake has multiple caching mechanisms. Query result cache is different from the local disk cache (SSD cache) on virtual warehouses and the remote disk cache (data cache).
7. Default behavior - Remember that query result reuse is ENABLED by default. Questions may ask about default settings.
8. Cross-user capability - Results can be reused across different users if they have appropriate access privileges to the data.
9. Session parameter name - The parameter USE_CACHED_RESULT controls this feature. Know how to enable or disable it.