Data Source Configuration Properties

The source configuration of a JDBC data source represents the capabilities of the underlying database. That is, it stores a list of the SQL operations and functions this database supports, the comparison operators it supports, etc. The Execution Engine uses this information to build the queries it executes in a database, with the goal of pushing down to the data source as much processing as possible, to optimize response times and minimize traffic through the network. Each database adapter defines a default source configuration. The default source configuration is different for each adapter because the capabilities of let us say Oracle, are different than the capabilities of SQL Server.

It is an uncommon that you need to modify the source configuration of a data source since the default options are tailored to the database you are connecting to. However, you can do so with this command:

ALTER DATASOURCE JDBC "<data source name>"
          [ <source configuration property>
        [ , <source configuration property> ]* ]

The page Data Source Configuration Properties of the VQL Guide lists all the properties you can modify in the source configuration of a data source. In addition to using the command ALTER DATASOURCE JDBC, you can use Design Studio to modify some these properties of the source configuration:

  • Allow literal as parameter. If yes, it indicates that the source allows the literals to be indicated as parameters of the prepared statement created to execute the view. If no, the Server generates the query with the literals in it.

  • Block size. It indicates the amount of data that the data source reads or writes in a single random I/O operation.

  • Multi block read count. It indicates how many consecutive blocks a database reads on a single I/O operation.

    The section Data Source I/O Parameters explains how the cost-based optimizer uses the parameters Block size and Multi block read count.

Only for JDBC data sources with the database adapter Generic:

  • Delegate aggregate functions list. List of aggregation functions that can be delegated.

  • Delegate scalar functions list. List of scalar functions that can be delegated.

  • Delegate operators list. List of operators that can be delegated. The default list has the following operators: =, <>, <, <=, >, >=, between, exists, in, is false, is null, is not null, is true, like and notin.

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