Snowflake Clustering: How To Use It To Enhance Query Performance

Snowflake Clustering: Improving query performance through data clustering.
May 29, 2024

Snowflake clustering is a technique that groups related rows in Snowflake tables into the same micro-partition to improve query performance. This organization of data allows Snowflake to avoid scanning unnecessary micro-partitions.

What is Snowflake Clustering?

Snowflake clustering involves physically grouping similar values of one or more columns together. Users can manually define the clustering key to control how Snowflake creates micro-partitions. Snowflake automatically clusters data into micro-partitions to allow for faster retrieval of frequently requested data.

CREATE TABLE my_table (
id INT,
event_date DATE,
event_type STRING,
CLUSTER BY (event_date, event_type);

This code snippet shows how to create a table with clustering keys defined. By clustering on event_date and event_type, related rows are grouped into the same micro-partitions, improving query performance.

What are the Benefits of Snowflake Clustering?

Snowflake clustering offers several benefits that enhance query performance and data management. These benefits include:

  • Improved Scan Efficiency: Clustering reduces the number of micro-partitions scanned during queries, leading to faster query execution times.
  • Better Column Compression: Clustering similar values together improves columnar compression, reducing storage costs.
  • Minimal Administration: Once clustering keys are defined, Snowflake automatically manages the clustering process, requiring minimal manual intervention.

How Does Snowflake Clustering Improve Query Performance?

Clustering in Snowflake is typically worth it on tables greater than 1 TB. Query performance is the best indicator of how well-clustered a table is. If queries on a table are performing as needed or expected, the table is likely well-clustered. If query performance degrades over time, the table is likely no longer well-clustered and may benefit from clustering.

  • Cluster columns that are most actively used in selective filters: Prioritize columns that are frequently used in WHERE clauses to improve scan efficiency.
  • Date-based queries: For fact tables involved in date-based queries, choose the date column as a clustering key.
  • Event type: For event tables, clustering by event type can improve performance for queries filtering by event type.

How to Implement Snowflake Clustering

1. Define Clustering Keys

To create a table with Snowflake clustering enabled, define clustering keys during the table's creation or alteration using the CREATE TABLE or ALTER TABLE commands.

ALTER TABLE my_table
CLUSTER BY (event_date, event_type);

This command alters an existing table to include clustering keys.

2. Insert Data into the Table

After defining clustering keys, insert data into the table. Snowflake automatically reorganizes data into micro-partitions based on the clustering keys defined for the table.

INSERT INTO my_table (id, event_date, event_type, ...)
VALUES (1, '2023-01-01', 'click', ...);

Data insertion triggers the clustering process, grouping related rows into micro-partitions for optimized query performance.

3. Evaluate Clustering Effectiveness

Evaluate how your table is clustered by looking at certain columns that your users will interface with. Use the SYSTEM$CLUSTERING_INFORMATION function to return clustering information, including average clustering depth.


This function helps monitor the clustering health of a large table and determine if it would benefit from explicitly defining a clustering key.

When Should You Use Snowflake Clustering?

Snowflake clustering is best suited for tables that meet specific criteria. Use clustering when:

  • Large Tables: The table contains at least 1,000 micro-partitions, indicating it holds multiple terabytes of data.
  • Frequent Queries: The table is queried frequently with many SELECT operations relative to UPDATE or DELETE operations.
  • Clustering Key Efficiency: A high percentage of queries can benefit from the same clustering key(s).
  • Infrequent Updates: The table is queried frequently but updated infrequently, making clustering more effective.
  • Filtered or Grouped Fields: The table has specific fields that are often filtered on or grouped by in queries.

Common Challenges and Solutions To Clustering

Discuss common challenges or errors that might occur while following the tutorial and provide solutions.

  • Degraded Query Performance: If query performance degrades over time, consider re-clustering the table by manually sorting rows on key table columns and re-inserting them.
  • High Clustering Costs: Clustering consumes credits, so it should only be used when queries will benefit substantially from it. Evaluate the cost-effectiveness before implementing clustering.
  • Frequent Updates: Clustering is most effective for tables that are queried frequently but updated infrequently. For tables with frequent updates, consider alternative optimization techniques.

Recap of Snowflake Clustering

Summarize the key takeaways from the tutorial and encourage the reader to apply what they've learned.

  • Improved Query Performance: Clustering groups related rows into micro-partitions, reducing the number of micro-partitions scanned during queries.
  • Automatic Clustering: Snowflake automatically reorganizes data based on defined clustering keys, requiring minimal administration.
  • Cost-Effective for Large Tables: Clustering is most beneficial for large tables with frequent queries and infrequent updates.

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