GUID clustered indexes vs. RID

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GUID clustered indexes vs. RID

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WayneS SSC Guru Points: 95460 More actions · Answer 1

I just read through this thread, and what I found interesting was what was missing (or, I just failed to see it...)

The keys in a clustered index are used in all non-clustered indexes (and if there isn't a clustered index, the hidden "Row ID" column (mentioned above) is used) to provide a lookup path back to the row. This means that in addition to a GUID column, the 16 bytes it takes up in storage space is also used in all non-clustered indexes. An integer identity column only uses 4 bytes. So, using an integer uses only 1/4 the space in the table, and saves 12 bytes * # rows * # non-clustered indexes. The space savings can really add up.

Wayne
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Johan Bijnens SSC Guru Points: 135369 More actions · Answer 2

WayneS (10/16/2010)
I just read through this thread, and what I found interesting was what was missing (or, I just failed to see it...)
The keys in a clustered index are used in all non-clustered indexes (and if there isn't a clustered index, the hidden "Row ID" column (mentioned above) is used) to provide a lookup path back to the row. This means that in addition to a GUID column, the 16 bytes it takes up in storage space is also used in all non-clustered indexes. An integer identity column only uses 4 bytes. So, using an integer uses only 1/4 the space in the table, and saves 12 bytes * # rows * # non-clustered indexes. The space savings can really add up.

That is indeed an extra negative side effect. ( caused by the way sqlserver implemented clustering indexes )

Johan

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Rob Schripsema SSCertifiable Points: 7469 More actions · Answer 3

WayneS (10/16/2010)
I just read through this thread, and what I found interesting was what was missing (or, I just failed to see it...)
The keys in a clustered index are used in all non-clustered indexes (and if there isn't a clustered index, the hidden "Row ID" column (mentioned above) is used) to provide a lookup path back to the row. This means that in addition to a GUID column, the 16 bytes it takes up in storage space is also used in all non-clustered indexes. An integer identity column only uses 4 bytes. So, using an integer uses only 1/4 the space in the table, and saves 12 bytes * # rows * # non-clustered indexes. The space savings can really add up.

Yes, a very good point. Hadn't thought of that.

Rob Schripsema
Propack, Inc.