When does a Snapshot Transaction Really Begin?
Category:
isolation-levels
, sql-server
They say, “never read the comments” on the internet, but I’m lucky to get lots of interesting points and questions in my comments.
Category: sql-server
When does physical reads include read-ahead reads in SQL Server?
Category:
query-performance
, sql-server
SQL Server has more than one way to pull pages in from disk for your queries. SQL Server can do a physical read of an 8KB page, or an extent of 8 of those 8KB pages.
Top 5 Misleading SQL Server Performance Counters
Perfmon counters are an excellent tool for monitoring and sometimes troubleshooting Microsoft SQL Server. But some counters can get you into trouble, because they don’t mean what many people think. Learn what to look out for in the world of widely-used perfmon counters.
Database Mirroring Counters Missing from Perfmon?
Category:
monitoring-troubleshooting
, sql-server
Collecting perfmon counters from SQL Server databases where you are using database mirroring is a little tricky
The counters won’t behave “normally” until after you set up mirroring for a database.
Finding Queries that Cause Wait Stats in SQL Server
Category:
monitoring-troubleshooting
, sql-server
You’ve got some troubling wait stats in SQL Server. How can you tell which queries are causing those waits?
Learn the pros and cons of different techniques to track down the cause of both common and tricky waits in SQL Server, including CXPACKET, PAGEIOLATCH, LCK, RESOURCE_SEMAPHORE, and THREADPOOL waits.
When a Nonclustered Index and Statistics Make a Query Slower
Nonclustered indexes are awesome in SQL Server: they can get you huge performance gains.
But we can’t always create the perfect index for every query. And sometimes when SQL Server finds an index that isn’t quite perfect and decides to use it, it might make your query slower instead of faster.
Removing Query Hints with Plan Guides (Dear SQL DBA Episode 43)
If you need to add, remove, or replace hints from ad-hoc queries where you can’t change the code, plan guides can help. See a demo of removing a query hint from parameterized TSQL run from an application, and get tips on how to make your plan guides work in SQL Server.