Indexing in Azure Synapse Dedicated SQL Pool Explained – Columnstore, Heap, Clustered & Rebuild Tips
📘 Introduction
Indexes in Azure Synapse Dedicated SQL Pool play a crucial role in optimizing query performance and storage. Synapse supports multiple types of indexes depending on your workload type—batch analytics, lookups, or staging data.
This blog covers:
- Clustered Columnstore Index
- Heap Tables
- Clustered Index
- Nonclustered Index
- Index Rebuild Tips
🔹 1. Clustered Columnstore Index (Default & Best for Analytics)
Best suited for large, analytical workloads. This index compresses data and improves performance. It's the default if no index is specified.
CREATE TABLE dbo.SalesFact_Columnstore
(
SaleID INT,
CustomerID INT,
Amount FLOAT,
SaleDate DATE
)
WITH (
CLUSTERED COLUMNSTORE INDEX,
DISTRIBUTION = HASH(CustomerID)
);
🔹 2. Heap Table (No Index)
No indexes are applied. Ideal for fast loading in staging or transient tables where performance tuning is not required yet.
CREATE TABLE dbo.SalesFact_Heap
(
SaleID INT,
CustomerID INT,
Amount FLOAT,
SaleDate DATE
)
WITH (
HEAP,
DISTRIBUTION = ROUND_ROBIN
);
🔹 3. Clustered Index (Rowstore)
Stores data in a sorted row-based format. Best for small dimension or lookup tables and selective filters.
CREATE TABLE dbo.Customer_Detail
(
CustomerID INT NOT NULL,
FullName NVARCHAR(100),
Region NVARCHAR(50)
)
WITH (
CLUSTERED INDEX (CustomerID),
DISTRIBUTION = HASH(CustomerID)
);
🔹 4. Nonclustered Index
Creates a separate index on one or more columns for faster lookups. Use selectively as each index adds overhead.
CREATE INDEX idx_Region ON dbo.Customer_Detail(Region);
🔄 5. Rebuilding Indexes (Especially for Columnstore)
Rebuilding restores compression and performance. Ideal for maintenance schedules, especially after heavy loads or updates.
-- Rebuild all indexes on a table
ALTER INDEX ALL ON dbo.SalesFact_Columnstore REBUILD;
-- Rebuild a specific partition (if partitioned)
-- ALTER INDEX ALL ON dbo.SalesFact_Columnstore REBUILD PARTITION = 1;
-- Optional compression setting
-- ALTER INDEX ALL ON dbo.SalesFact_Columnstore
-- REBUILD PARTITION = 1 WITH (DATA_COMPRESSION = COLUMNSTORE);
✅ Best Practices
- Use CLUSTERED COLUMNSTORE for large fact tables and analytics.
- Use HEAP for fast, staging loads or temporary tables.
- Use CLUSTERED INDEX for small dimension or lookup tables.
- Use NONCLUSTERED INDEX for tuning specific query filters.
- Rebuild indexes regularly to maintain performance.
⚠️ Note: Index rebuilds are offline operations — schedule them during maintenance windows.
📺 Watch the Video Tutorial
📚 Credit: Content created with the help of ChatGPT and Gemini.