SQL Plan Archives - Page 11 of 12

The Halloween Problem – Part 4

The Halloween Problem has a number of important consequences for SQL Server execution plans. In this final part of the series, we look at some of the tricks the optimizer uses to avoid adding an Eager Table Spool to every update query that might encounter the Halloween Problem.

Paul White ◆ February 20, 2013

15

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

4

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

4

The Halloween Problem – Part 1

Much has been written over the years about understanding and optimizing SELECT queries, but rather less about data modification. This series of posts looks at an issue that is specific to INSERT, UPDATE, DELETE and MERGE queries – the Halloween Problem.

Paul White ◆ February 13, 2013

9

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

5

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

8

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

14

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

27

The Benefits of Indexing Foreign Keys

Primary and foreign keys are fundamental characteristics of relational databases, as originally noted in E.F. Codd’s paper, “A Relational Model of Data for Large Shared Data Banks”, published in 1970. The quote often repeated is, "The key, the whole key, and nothing but the key, so help me Codd."

In this post, Erin Stellato (@erinstellato) discusses the benefits of adding indexes on top of declared referential constraints.

Erin Stellato ◆ November 20, 2012

16

Ten Common Threats to Execution Plan Quality

The quality of an execution plan is highly dependent on the accuracy of the estimated number of rows output by each plan operator. If the estimated number of rows is significantly skewed from the actual number of rows, this can have a significant impact on the quality of a query's execution plan. Poor plan quality can be responsible for excessive I/O, inflated CPU, memory pressure, decreased throughput and reduced overall concurrency.

Joe Sack ◆ November 13, 2012

11

Bad cardinality estimates coming from SSMS execution plans

I have a few people to thank for a recent update to Plan Explorer. Brooke Philpott (@Macromullet) and Greg Gonzalez (blog | @SQLsensei), of course, for R & D and for digging into the code and sorting it out. But also to Paul White for being persistent in helping us validate the fixes.

Aaron Bertrand ◆ November 2, 2012

0