SQL Server GUIDS (Globally Unique Identifiers)
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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.
SQL Server GUIDS (Globally Unique Identifiers)
- 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
- 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/