Are Bad Statistics Making My Query Slow? (Dear SQL DBA Episode 39)

An important query is suddenly slow. Is it because statistics are out of date? This is tricky to figure out, and updating statistics right away can make troubleshooting even harder. Learn how to use query execution plans to get to the heart of the question and find out if stats are really your problem, or if it’s something else.

In this 35 minute episode:

• 00:39 SQL Server 2017 Announced
• 01:10 New video from Microsoft’s Joe Sack demonstrating Adaptive Query Processing
• 03:05 This week’s question: Are bad stats making my query slow?
• 05:26 Demo of finding plan in cache and analyzing stats begins
• 28:17 What to do when stats ARE the problem

Code samples are at the bottom of the page

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Columnstore Index Returns Zero Rows... Which is One Row

I’ve never claimed to be great at math, but until recently I thought I knew how to count to one. Zero… one. That’s what we learned in kindergarten.

Apparently SQL Server didn’t go to kindergarten.

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What is that Garbage in my Execution Plan? (Dear SQL DBA Episode 27)

Today I was working on some code samples for a user question, and I hit a weird roadblock.

There was a bunch of garbage in my execution plan that I couldn’t explain. And by ‘garbage’, I mean a nested loop to a whole branch of code that I hadn’t asked SQL Server to run – and a warning about an implicit conversion possibly causing problems with the quality of my execution plan.

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Parallelism and tempdb data file usage in SQL Server

I’m sometimes asked if the number of CPU cores used by a query determines the number of tempdb files that the query can use.

Good news: even a single threaded query can use multiple tempdb data files.

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Columnstore Indexes and Computed Columns in SQL Server 2016

You can’t do everything with a columnstore index – but SQL Server’s optimizer can get pretty creative so it can use a columnstore index in ways you might not expect.

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Why is My Query Faster the Second Time it Runs? (Dear SQL DBA Episode 23)

Today’s question is about why a query might be slow at first, then fast the next time you run it.

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Estimated vs. Actual Number of Rows in Nested Loop Operators

This is one of those little details that confused me a ton when I was first working with execution plans.

One problem with learning to work with plans is that there’s just SO MUCH to look at. And it’s a bit spread out. So, even when looking at a single tooltip, things can be confusing.

Let’s talk about the nested loop operator, who can be particularly weird to understand.

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