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Tuesday, July 15, 2008 2:03 PM

Partitioned Tables in SQL Server 2008

In this post , I introduced how SQL Server 2005 implements query plans on partitioned tables. If you've read that post or used partitioned tables, you may recall that SQL Server 2005 uses a constant scan operator to enumerate the list of partition ids
Posted by craigfr | 2 Comments
Thursday, May 15, 2008 9:39 AM

Query Processing Presentation

Last week, I had the opportunity to talk to the New England SQL Server Users Group . I would like to thank the group for inviting me, Adam Machanic for organizing the event, and Red Gate for sponsoring it. My talk was an introduction to query processing,
Posted by craigfr | 0 Comments
Attachment(s): QPTalk.pdf
Wednesday, May 09, 2007 7:57 AM

Repeatable Read Isolation Level

In my last two posts, I showed how queries running at read committed isolation level may generate unexpected results in the presence of concurrent updates. Many but not all of these results can be avoided by running at repeatable read isolation level.
Posted by craigfr | 1 Comments
Wednesday, April 25, 2007 9:59 AM

Read Committed Isolation Level

SQL Server 2000 supports four different isolation levels: read uncommitted (or nolock), read committed, repeatable read, and serializable. SQL Server 2005 adds two new isolation levels: read committed snapshot and snapshot. These isolation levels determine
Posted by craigfr | 5 Comments
Monday, November 27, 2006 11:56 AM

Introduction to Partitioned Tables

In this post, I’m going to take a look at how query plans involving partitioned tables work. Note that there is a big difference between partitioned tables (available only in SQL Server 2005) and partitioned views (available both in SQL Server 2000 and
Posted by craigfr | 1 Comments
Wednesday, November 01, 2006 9:16 PM

Parallel Scan

In this post, I’m going to take a look at how SQL Server parallelizes scans. The scan operator is one of the few operators that is parallel “aware.” Most operators neither need to know nor care whether they are executing in parallel; the scan is an exception.
Posted by craigfr | 3 Comments
Wednesday, October 18, 2006 9:54 AM

Index Union

I was planning to continue writing about parallelism this week (and I will continue another time in another post), but I received an interesting question and chose to write about it instead. Let’s begin by considering the following query: create table
Posted by craigfr | 0 Comments
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Thursday, July 13, 2006 1:12 PM

Index Examples and Tradeoffs

The optimizer must choose an appropriate “access path” to read data from each table referenced in a query. The optimizer considers many factors when deciding which index to use, whether to do a scan or a seek, and whether to do a bookmark lookup. These
Posted by craigfr | 2 Comments
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Friday, July 07, 2006 1:36 PM

Seek Predicates

Before SQL Server can perform an index seek, it must determine whether the keys of the index are suitable for evaluating a predicate in the query. Single column indexes Single column indexes are fairly straightforward. SQL Server can use single column
Posted by craigfr | 4 Comments
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Friday, June 30, 2006 1:05 PM

Bookmark Lookup

In my last post, I explained how SQL Server can use an index to efficiently locate rows that qualify for a predicate. When deciding whether to use an index, SQL Server considers several factors. These factors include checking whether the index covers
Posted by craigfr | 9 Comments
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Monday, June 26, 2006 2:40 PM

Scans vs. Seeks

Scans and seeks are the iterators that SQL Server uses to read data from tables and indexes. These iterators are among the most fundamental ones that we support. They appear in nearly every query plan. What is the difference between a scan and a seek?
Posted by craigfr | 2 Comments
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