I frequently need to see rowcounts and execution time for queries while they’re running. Maybe I’m troubleshooting a slow query that’s still executing, or I want to understand which operators are causing the slowdown before the query completes.
Last week at the PASS Summit I learned some little nuances about how this works that I’d missed.
This is the worst bug I’ve found in SQL Server to date. Previously, my top find was SQL Server Online Index Rebuild sometimes happens offline without warning. This one has taken top slot because it makes my life more difficult on a daily basis.
Background: SQL Server generates a query_hash for each query. This is stored in sys.query_store_query and it’s one of the primary ways you can identify what a query is across different Query Stores, or even the same Query Store over time, as surrogate query_id values get reset if Query Store is cleared or data ages on. The query_hash is a ‘Zobrist hash over the shape of the individual query, based on the bound (input) logical query tree. Query hints aren’t included as part of the hash.’ (Source)
I’m introducing a series of “learner’s guides”: overviews of a given topic, chock full of links and references. For this first post, the information is based on what I learned when I was part of the team at Brent Ozar Unlimited who put together the original First Responder Kit and built a related consulting practice using those tools.
I’ve just published a new SQLChallenge course, and I think it’s one of the best ones yet.
Your mission is to:
In the solution videos, I’ll step through multiple strategies to figure out which statement in the procedure is slowing it down the most – because in real life, you need to have a whole bag of tricks in different situations.
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.
This week’s ‘Dear SQL DBA’ question gets us down to the essentials: how to I tell if a transaction is hanging?
Psssttt – I have an updated blog post on this called the Learner’s Guide to SQL Server Performance Tuning
The SQL Server is slow, what should you do? I answer a reader question and share my strategy for performance troubleshooting.
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