SQL Performance Archives - Page 28 of 31

The Halloween Problem – Part 3

The MERGE statement (introduced in SQL Server 2008) allows us to perform a mixture of INSERT, UPDATE, and DELETE operations using a single declarative statement. The Halloween Protection issues for MERGE are, logically enough, mostly a combination of the requirements for the individual operations performed, but there are some important differences and a couple of optimizations that apply only to MERGE.

Paul White ◆ February 18, 2013

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The Halloween Problem – Part 2

In the first part of this series, we saw how the Halloween Problem applies to UPDATE queries. In this post, we will see how the same underlying issue can affect INSERT and DELETE statements.

Paul White ◆ February 15, 2013

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If you are using indexed views and MERGE, please read this!

Here is some information about an important MERGE "wrong results" bug, involving indexed views, that could be affecting the accuracy of your queries right now, and what options you have for working around the problem.

Aaron Bertrand ◆ February 6, 2013

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Trimming More Transaction Log Fat

In my previous post on streamlining the operations of the transaction log, I discussed two of the most common causes of extra log records being generated: dead weight from unused nonclustered indexes and page split operations (that cause index fragmentation). Assuming you’ve read that post, I mentioned that there are more subtle problems that can be detrimental to transaction log performance, and I’m going to cover these here.

Paul Randal ◆ January 22, 2013

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Generate a set or sequence without loops – part 3

Earlier in this series (Part 1 | Part 2) we talked about generating a series of numbers using various techniques. While interesting, and useful in some scenarios, a more practical application is to generate a series of contiguous dates; for example, a report that requires showing all the days of a month, even if some days had no transactions.

Aaron Bertrand ◆ January 18, 2013

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Generate a set or sequence without loops – part 2

In my previous post, I talked about ways to generate a sequence of contiguous numbers from 1 to 1,000. Now I'd like to talk about the next levels of scale: generating sets of 50,000 and 1,000,000 numbers.

Aaron Bertrand ◆ January 17, 2013

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Generate a set or sequence without loops – part 1

There are many use cases for generating a sequence of values in SQL Server. I'm not talking about a persisted IDENTITY column (or the new SEQUENCE in SQL Server 2012), but rather a transient set to be used only for the lifetime of a query. Or even the simplest cases – such as just appending a row number to each row in a resultset – which might involve adding a ROW_NUMBER() function to the query (or, better yet, in the presentation tier, which has to loop through the results row-by-row anyway).

Aaron Bertrand ◆ January 16, 2013

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Selecting a Processor for SQL Server 2012

Since Microsoft revamped the licensing model for SQL Server 2012, it is especially important to do some thoughtful analysis before you decide exactly which processor to use for a database server that will be running SQL Server 2012. The move to core-based licensing for SQL Server 2012 Enterprise Edition means that a careless decision about precisely what processor you will be running on can cost both a great deal of money and a great deal of performance and scalability.

Glenn Berry ◆ January 9, 2013

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Should I use NOT IN, OUTER APPLY, LEFT OUTER JOIN, EXCEPT, or NOT EXISTS?

SQL Sentry's Aaron Bertrand (@AaronBertrand) digs into the left anti semi join, comparing NOT IN, NOT EXISTS, OUTER APPLY, EXCEPT, and OUTER JOIN methods.

Aaron Bertrand ◆ December 27, 2012

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Trimming the Transaction Log Fat

In many SQL Server workloads, especially OLTP, the database’s transaction log can be a bottleneck that adds to the time it takes a transaction to complete. Most people assume that the I/O subsystem is the real bottleneck, with it not being able to keep up with the amount of transaction log being generated by the workload.

Paul Randal ◆ December 17, 2012

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TRANSACTION_MUTEX and Multi-Session Transaction Access

I recently encountered high TRANSACTION_MUTEX accumulated wait time on a client system. I couldn’t recall a case where I saw this wait type as near the top of the “high waits” list and I was curious about what factors could push this type of overall wait time.

The Books Online definition of TRANSACTION_MUTEX is that it "occurs during synchronization of access to a transaction by multiple batches." Not many areas within the SQL Server engine expose this type of functionality, so my investigation was narrowed down to the following technologies:

Joe Sack ◆ December 10, 2012

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