Cardinality Estimation for a Predicate on a COUNT Expression
Paul White takes you on an optimizer journey, exploring how SQL Server comes up with cardinality estimates for COUNT queries.
2017-05-17
3,222 reads
Cardinality Estimates
Bad Cardinality Estimates from SSMS Plans – Redux
Aaron Bertrand shares some insight about early changes to Plan Explorer that help to provide you with the most accurate information we can.
2016-04-04
2,780 reads
Fixing Gatekeeper Row Cardinality Estimate Issues
The Query Optimiser needs a good estimate of the number of rows likely to be returned by each physical operator in order to select the best query plan from the most likely alternatives. Sometimes these estimates can go so wildly wrong as to result in a very slow query. Joe Sack shows how it can happen with SQL Queries on a data warehouse with a star schema.
2012-12-10
1,163 reads
Blogs
How to Find Expensive Queries in Amazon Redshift
Slow-running queries can degrade your Redshift cluster’s performance and lead to increased costs. Identifying...
The Notification Trap: How Input Fatigue Is Killing Deep Work in Tech
By gbargsley
If you've been here before, you know this blog is usually about SQL Server,...
Designing a Storage Load Test for SQL Server
I’ve been doing storage load tests for SQL Server for a long time, both...
Forums
How Long is a Long I/O?
Comments posted to this topic are about the item How Long is a Long...
T-SQL Trigonometric Functions in SQL Server
Comments posted to this topic are about the item T-SQL Trigonometric Functions in SQL...
Half of All Engineers
Comments posted to this topic are about the item Half of All Engineers
Question of the Day
How Long is a Long I/O?
In SQL Server 2025, a long I/O is recorded in the error log with message 833. How long much an I/O request be outstanding before this message is written to the log?
See possible answers