2. Understanding Ingres Star Architecture : Query Optimizer
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Query Optimizer
Ingres uses a query optimizer to develop sophisticated query execution strategies. The optimizer makes use of the following kinds of information:
Table size
Number of rows in a table
Data-related information such as the amount of duplication in data values within a column and distribution of data values
Network costing factor
Ingres Star maintains statistical data in a catalog named iistatistics, and data about the distribution of data in a table named iihistograms.
Ingres Star supports a distributed query optimizer to choose the most efficient access or query plan between different databases and between different nodes.
When developing the query plan, Ingres Star has the ability to move data rows from one site to another in order to maximize processing resources while minimizing data movement.
Ingres Star can analyze line cost factors between nodes and remote-node CPU processing performance and choose whether and where to transfer data for optimum performance.
For additional information on the Ingres query optimizer, see the Database Administrator Guide. The detailed steps for viewing query plans can be found in the online help.