The document presents an overview of Global Unique Identifiers (GUIDs), detailing their generation, advantages, and disadvantages. GUIDs have a unique 16-byte size, can be generated offline, and are beneficial for identifying data from multiple sources; however, they lead to larger data sizes, slower performance on joins/updates, and increased index fragmentation. The presentation includes demos and resources for further exploration of GUIDs.

1. Unique Identifiers - GUIDs
Presentation by Aaron Buma
Development DBA

2. Session Overview
• Overview
• Generation
• Comparison and Non-Comparison Operations
• Advantages and Disadvantages

3. GUID Overview
• GUID – Global Unique Identifier
• Unique – 2^128 possible values
• A unique 16-byte number
• Can be auto-generated on a column
– IDENTITY and TIMESTAMP (2008-)/ROWVERSION(2008+)

4. GUID Generation
• On the fly:
• From a String (too long of string will be trimmed):
• Auto-Generate:

5. GUID Generation
• NEWID:
– A random 16 byte identifier
• NEWSEQUENTIALID:
– Can only be a DEFAULT when record is created

6. Comparison (and non) Operations
Can Use Can’t Use
=, !=, <> +, -, *, /
<, <=, >, >=
LIKE
BETWEEN
IS NULL and IS NOT NULL

7. GUIDs and ORDER BY
• When using “ORDER BY” on a GUID column, the data
is sorted on the last section of the GUID

8. DEMOS

9. Advantages of GUIDs
• Identifying data from multiple sources
– An advantage over IDENTITY
• Can be generated offline

10. Disadvantages of GUIDs
• Data Size: 4x larger than INT
– Slower and Larger Indexes
– Page Splits on Indexes (fragmentation)
• Slowest JOIN performance
• Slowest INSERT/UPDATE performance
• Slowest SORT performance

11. Disadvantages of GUIDs
• Adding/Removing GUIDs will cause fragmentation on
indexes if GUIDs are used for:
– Primary Keys
• GUIDs have least performance on JOINS, so not only is
JOINING on a GUID slow, but joining to a fragmented
index is even slower
– Clustering

12. Advantage vs Disadvantages
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13. Review
• Overview
• Generation
• Comparison and Non-Comparison Operations
• Advantages and Disadvantages
Presentation Recording, Slides and Scripts
– Available at:
http://www.aaronbuma.com/2015/10/guids/