Database Administration (MOSC)

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NOT NULL to NULL - Why so much IO?

edited May 14, 2014 9:11AM in Database Administration (MOSC) 17 commentsAnswered

I have a 1.2 TB table - not partitioned - with a column that was added wrongly by a vendor as NOT NULL. This is in 11.2.0.4.2.

Why does changing that to NULL require the database to read every single row (apparently more than once)? There is no index on this column and there are no referential constraints on it.

Shouldn't that just be a dictionary change?

Thanks,

Bryan

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