Different Execution Plans

Hi, I have a derived view expecting to run 2 base views parallely and do a join operation in denedo server with the base view results from source server. Even the execution plan in the derived view shows me the same but actual plan is different. On source server I can see that Join statement of both base views is being executed. Why is the projected execution plan different from actual execution plan.
user
26-04-2017 09:44:41 -0400

1 Answer

Hi, In Virtual DataPort Administration tool, you could view how a query is fetching data from its data source by two ways, * Query plan - It is a execution plan that Virtual DataPort used to run a query. Query plan gives you a view of the execution plan of the query but not the details of a specific execution. * Execution Plan - It specifies which sub-queries have to be executed in each data source and what transformation or combination operations will be required within Denodo. The execution of sub-queries in data sources takes place in parallel, improving performance. When I executed a derived view in Virtual DataPort, the join between two base view is delegated to the data source due to query optimization. In derived view the key aspect of query optimization is the execution strategy of the join operations involved in the query. The execution strategy for a join consists of method used to implement the join operation and the order in which the join input views are considered. Virtual DataPort supports the execution methods like Hash, Merge, Nested and Nested parallel. You could refer the section “Optimizing Join Operations” in [Virtual DataPort Administration Guide](https://community.denodo.com/docs/html/browse/6.0/vdp/administration/index). Hope this helps!
Denodo Team
03-05-2017 08:53:36 -0400
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