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Denodo 6 "Create base view from query" vs Denodo 5.5 "Create base view from query"

Hi, In Denodo 5.5, when I create a base view from a query Denodo doesn't seem to ever delegate that query to the data source, even when I include a restrictive where clause... and thus the query takes a long time to run. In Denodo 6, it appears the default behavior is to wrap the query from the base view in a subquery and to then delegate it to the data source (the "Delegate Sub Query" Source Configuration seems to control this). Thus, in Denodo 6, I've noticed that Denodo is able to take the same query it receives from my client application and run much much faster. So, here is my question: In Denodo 5.5, I've always told developers "Never use 'create base view from query' because of performance implications". However, in Denodo 6, because of the subquery delegation, what should I tell my developers? "Avoid using 'create base view from query', but it might be okay to use it from time to time"? Thanks~!
12-07-2016 16:22:06 -0400

1 Answer

Hi! The “Delegate as Subquery” option already existed in Denodo 5.5. In Denodo 6.0 version this check is enabled by default. Regarding the “Create base view from query” best practices, my recommendation is to avoid creating base views using this option if you can create the base view graphically. Views created from queries limit the query optimization that VDP applies like removing unnecessary join branches, changing the join method, recording the joins, etc. In addition, in those kind of views, the indexes, primary keys and statistics cannot be imported from the source. In short, I would use the “Create base view from query” option as the last alternative in situations like very complex and tunned SQL queries or to execute a store procedure of the source database and get its results. Hope this helps!
Denodo Team
13-07-2016 09:15:00 -0400
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