In this blog post, we will delve into the world of SQL Server ColumnStore Indexes and how we can use Extended Events to gain insights into their behavior. If you have been working with ColumnStore Indexes or are interested in learning more about them, this article is for you.

ColumnStore Indexes are a powerful feature in SQL Server that can significantly improve query performance for large data sets. They store data in a columnar format, allowing for efficient compression and query execution. However, understanding how ColumnStore Indexes work and identifying any performance issues can be challenging.

Traditionally, SQL Server Profiler has been a popular tool for capturing and analyzing query execution events. However, when it comes to ColumnStore Indexes, Profiler falls short as it does not provide specific events related to their behavior. This is where Extended Events come into play.

Extended Events is a lightweight performance monitoring system in SQL Server that allows you to capture and analyze events at a granular level. It provides a wide range of events and actions that can be used to monitor various aspects of SQL Server, including ColumnStore Indexes.

Let’s take a look at some of the key Extended Events that can help us understand and troubleshoot ColumnStore Indexes:

• Query Execution – batch_hash_table_build_bailout: This event occurs when the batch operation to build a hash table encounters a low memory condition and switches to row mode operation. By capturing this event, we can identify performance issues caused by low memory conditions.
• Storage Engine related events: These events provide insights into how the storage engine behaves with ColumnStore Indexes. Some of the events include column_store_object_pool_hit, column_store_object_pool_miss, column_store_segment_eliminate, column_store_rowgroup_readahead_issued, and column_store_rowgroup_read_issued. Monitoring these events can help us understand the efficiency of the storage engine and identify any potential bottlenecks.
• Expression Services – expression_compile_stop_batch_processing: This event occurs when an expression is not natively supported in batch processing mode and a wrapper of row-by-row evaluation is used. By capturing this event, we can identify any performance impact caused by expressions that require row-by-row evaluation.

These are just a few examples of the many Extended Events available for monitoring ColumnStore Indexes. By leveraging Extended Events, DBAs and developers can gain valuable insights into the behavior of ColumnStore Indexes and optimize their performance.

In future blog posts, we will explore memory-related components and dive deeper into the storage aspects of ColumnStore Indexes. Stay tuned for more in-depth discussions on this topic.

If you have any experience using Extended Events for monitoring ColumnStore Indexes or have any specific use cases to share, please let us know in the comments below. We would love to hear from you!

Meanwhile, if you’re interested in learning more about how Extended Events can help with finding long-running queries, check out this blog post.