UNION ALL views for faster loads [CR 619105]

In Chapter 4, “Managing System Resources > Using UNION ALL views for faster load,” a new paragraph should be inserted after the first paragraph, so the section begins:

“UNION ALL views can be used to improve load performance where it is too expensive to maintain secondary indexes for all rows in a table. Sybase IQ lets you split the data into several separate base tables (for example, by date). You load data into these smaller tables. You then join the tables back together into a logical whole by means of a UNION ALL view, which you can then query.

This strategy can improve load performance, but may negatively impact the performance of some types of queries. Most types of queries have roughly similar performance against a single base table or against a UNION ALL view over smaller base tables, as long as the view definition satisfies all the constraints described in “Optimizing queries that reference UNION ALL views.” However, some types of queries, especially those involving DISTINCT or involving joins with multiple join columns, may perform significantly slower against a UNION ALL view than against a single large base table. Before choosing to use this strategy, determine whether the improvements in load performance are worth the degradation in query performance for your application.”