Parallel query was once considered mandatory for many data warehouses simply because in the past (say, in 1995), data warehouses were rare and typically had a very small, focused user base. Today in 2010, data warehouses are literally everywhere and support user communities that are as large as those found for many transactional systems. This means that you might not have sufficient free resources at any given point in time to enable parallel query on these systems. This doesn’t mean parallel execute is not useful in this case—it just might be more of a DBA tool, as we’ll see in the section “Parallel DDL,” rather than a parallel query tool.
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