Clustered Indexes

Derik Hammer looks at the power of clustered indexes:

The data in a clustered index is logically sorted but does not guarantee that it will be physically sorted. The physical sorting is simply a common misconception. In fact, the rows on a given page are not sorted even though all rows contained on that page will be appropriate to its place in the logical sort order. Also, the pages on disk are not guaranteed to be sorted by the logical key either.

The most likely time where you will have a clustered index that is physically sorted is immediately after an index rebuild operation. If you are trying to optimize for sequential reads, setting a fill factor to leave free space on your pages will help limit how often you have pages physically out of order at the expense of disk space.

Derik also discusses four qualities for a good clustered index.  My preferred acronym is NUSE (Narrow, Unique, Static, Ever-increasing); Derik uses slightly different terms.

Related Posts

Generating Index Drop And Create Statements

Drew Furgiuele says “Game over, man, game over!” to indexes: The premise is simple: it will generate a series of DROP and then CREATE INDEX commands for every index. The process is a little more complex in practice, but at a high level it: Creates a special schema to house a temporary object, Creates a […]

Read More

Index That Column Or Include It?

Jeanne Combrinck lays out her recommendations on whether to make a particular column part of an index or have it be an included column: The original question we wanted to answer was whether we would see a performance difference when a query used the index with all columns in the key, versus the index with […]

Read More

Categories

June 2016
MTWTFSS
« May Jul »
 12345
6789101112
13141516171819
20212223242526
27282930