11Aug 2009 by Grant Fritchey 3 Comments

Some Statement Start Times!

SQL Server, T-SQL
I thought I had captured statement start times within the DMV sys.dm_exec_sessions. I was absolutely wrong. However, this has sparked a bit of discussion, as you can see in the link to my correction. John Vanda (I couldn't find a blog by him, but I think this is his LinkedIn profile), suggested possibly joining between the sys.dm_exec_requests and sys.dm_tran_active_transactions through the transaction_id available in the requests DMV. He ran a series of tests that showed it to be promising. I re-ran my original test, a few long-running statements within a batch; BACKUP, CHECKDB, etc.. This time I captured the transaction information along with the other DMV's. The results were interesting. Rather than pull together any particular set of data as I was testing, I just collected all three DMV's once…
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31Jul 2009 by Grant Fritchey 13 Comments

No really. When did this statement start?

SQL Server
I thought I had an interesting answer to the question. Unfortunately Adam Machanic, who has been working in this specific area quite a bit longer than I have, and, let's face it, is a bit smarter, pointed out (in the comments) the possibility that I didn't have this quite right. I ran all his tests and sure enough, it wasn't working the same way that I saw it work. First, I tried modifying his query so that it ran the SELECT statements from the DMV's between the operations, but this didn't change the results, start_time and last_request_start_time were the same. From a scientific stand-point, if no one can replicate your results, the experiment failed. So I went back and tried again. To be sure I got things right and wasn't, somehow,…
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28Jul 2009 by Grant Fritchey 7 Comments

When did this statement start?

SQL Server, T-SQL
UPDATE: This post is incorrect. Adam nailed it in the comments. I explain my mistake here. A question came up over at SQL Server Central where someone was wondering if it was possible to know when a given statement within a batch started. Immediately I thought, oh yeah, that's easy, use the sys.dm_exec_requests dynamic management view (DMV). Done. Wrong. The original poster pointed out that I had assumed that the values present in the DMV represented statement level values, but they show the batch. While the DMV shows a start_time, that time is the start of the current batch, not the statement within the batch. Now the question was, where else might I get this data? I next tried sys.dm_exec_sessions because it has the last_request_start_time value. Sure enough this worked. Don't…
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20Jul 2009 by Grant Fritchey No Comments

MS Field Engineer’s on Performance Troubleshooting

SQL Server, T-SQL
Do you want to get a glimpse into how the Microsoft Field Engineers would go about troubleshooting performance issues on your server? Then go and read this blog entry by Denzil Ribeiro. Not only is this an excellent how-to on troubleshooting performance problems, but Mr. Ribeiro provides multiple links that describe the concepts he's dealing with further, making it a great piece of documentation. The MS Field Engineer blog is not terribly active, but what gets posted there is worth reading. If you don't have it on your feed list, you should.
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17Jul 2009 by Grant Fritchey 15 Comments

Execution Plan Compile Termination

SQL Server, T-SQL
Recently I've been seeing a lot of people with bad execution plans, desperately trying to tune them, but they were unable to explain why they had such bad plans. More often than no these were larger queries, with a number of derived tables, CTE's, CROSS APPLY, etc. In most cases the statistics appeared to be fine (this is usually checked by comparing estimated & actual rows within the operations in the execution plan) and the plans themselves didn't look crazy, but the execution plans were flat out, not good. If you're looking at a plan and it doesn't make much sense, one option that most people don't check... SQL Server didn't have enough time to complete optimization. The optimizer is a pretty amazing bit of code. The scary volume of…
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26Jun 2009 by Grant Fritchey No Comments

Re-evaluating Execution Plans (again)

SQL Server, T-SQL
I keep thinking I've got a handle on the way execution plans are dealt with in SQL Server. I had a pretty simplistic view of things, there's the estimated plan which comes out of the optimizer and there's the actual plan which comes out of the data engine. The one shows the best guess for what will happen based on the query and the underlying statistics. The other shows what actually happened based on the query and the real data, load on the server, available memory, you get the idea. This model is easy to explain and understand. Too bad it's not quite the way things work. If you query the dynamic management function sys.dm_exec_query_plan, you can see a query plan. Once you drill down on the XML, or browse…
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17Jun 2009 by Grant Fritchey No Comments

Object Database Editorial

nHibernate, Object Relational Mapping, SQL Server
I never used to read editorials. Not in emails, magazines, newspapers, whatever. Now, I make it a point of always reading them. You can learn as much from an editorial as you can from the technical articles within, sometimes more. Tony Davis has just posted a guest-editorial over at SQL Server Central. Tony is normally the editor at Simple-Talk, where he also writes interesting editorials. This one is not to be missed. It makes a very clear, and concise case for why object databases have a fundamental flaw for most business needs (not all, not always, but a pretty hefty majority). It's worth a read.
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08Jun 2009 by Grant Fritchey No Comments

Microsoft SQL Server Premier Field Engineers

SQL Server, T-SQL
Joe Sack has started a new team blog for the Microsoft SQL Server Premier Field Engineers. If you don't know who they are, you should. The first post is just introductory, but this blog is likely to become a great resource. These are the guys that MS zip lines into tough situations with the expectations that they'll improve them. I'd strongly suspect these are fellows worth listening to.
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27May 2009 by Grant Fritchey 16 Comments

WHOOOP!

PASS, SQL Server, T-SQL
I just got the good word, I submitted an abstract for a spotlight session at the PASS Summit and it was accepted. Jazzed doesn't begin to describe it. If you're interested in hearing what I think about Best Practices for working with Execution Plans, please swing by.
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20May 2009 by Grant Fritchey 5 Comments

Odd TSQL Behavior

SQL Server, T-SQL
Before I describe this, let me thank Lynn Pettis over at SQL Server Central for coming up with the answer. This morning a developer walked up and asked me what would happen if he ran a query that looked like this: SELECT 1.SomeString I said that he'd get an error. No, he says, try it. So I try it and I get this: Somestring 1 Try it yourself. It works just fine. I'd never seen that before and didn't have a clue what it was. Thinking that Microsoft had supplied some new short hand to define aliases I ran this: SELECT 'dude'.dudette Which resulted in the error:   Msg 258, Level 15, State 1, Line 1 Cannot call methods on varchar.   Which is what I would have expected. I…
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