Hypothetical indexes are leftovers from the Database Engine Tuning Advisor. They hold a name and statistics but no data. This post lists them, shows they cannot serve a query, and drops them in two steps: a list you read first, and a drop second.
How to Find Table Cardinality from the Execution Plan? – Interview Question of the Week #213
How to find table cardinality from the execution plan? I answer this health check question in two different ways, using a simple AdventureWorks query.
Update Statistics With FULLSCAN and MAXDOP in SQL Server
To update statistics with FULLSCAN in parallel, add MAXDOP to the statement. This post builds a table of 3 million rows, times the update with MAXDOP 1, the instance default and 8, and shows which statistics speed up and which do not.
SQL SERVER – Enabling Older Legacy Cardinality Estimation
Legacy Cardinality Estimation temporarily stabilized one customer memory-grant problem. A query waited on RESOURCE_SEMAPHORE while the instance became unresponsive.
SQL SERVER – Say No To Database Engine Tuning Advisor
I review Database Engine Tuning Advisor recommendations against the workload before applying them. That was the point behind my original opinion.
Does Parallel Threads Process Equal Rows? – Interview Question of the Week #211
Do parallel threads process equal rows? Usually no, and a simple AdventureWorks query with its actual execution plan proves it in a few seconds.
The Ascending Key Problem: Estimates for Today’s New Rows
Diagnose ascending key estimates with histogram boundaries, modification counts, and controlled comparisons before updating statistics.