FilterFactory Class

If you write a filter, you must also write a filter factory to produce filter instances. To do so, subclass the FilterFactory class.

Your subclass performs the initial validation and planning of the function execution and instantiates UDFilter objects on each host that will be filtering data.

Filter factories are singletons. Your subclass must be stateless, with no fields containing data. The subclass also must not modify any global variables.

FilterFactory Methods

The FilterFactory class defines the following methods. Your subclass must override the prepare() method. It may override the other methods.

Setting Up

Vertica calls plan() once on the initiator node, to perform the following tasks:

• Check any parameters that have been passed from the function call in the COPY statement and error messages if there are any issues. You read the parameters by getting a ParamReader object from the instance of ServerInterface passed into your plan() method.

• Store any information that the individual hosts need in order to filter data in the PlanContext instance passed as a parameter. For example, you could store details of the input format that the filter will read and output the format that the filter should produce. The plan() method runs only on the initiator node, and the prepare() method runs on each host reading from a data source. Therefore, this object is the only means of communication between them.

  You store data in the PlanContext by getting a ParamWriter object from the getWriter() method. You then write parameters by calling methods on the ParamWriter such as setString.

  Note: ParamWriter offers only the ability to store simple data types. For complex types, you need to serialize the data in some manner and store it as a string or long string.

Creating Filters

Vertica calls prepare() to create and initialize your filter. It calls this method once on each node that will perform filtering. Vertica automatically selects the best nodes to complete the work based on available resources. You cannot specify the nodes on which the work is done.

Defining Parameters

Implement getParameterTypes() to define the names and types of parameters that your filter uses. Vertica uses this information to warn callers about unknown or missing parameters. Vertica ignores unknown parameters and uses default values for missing parameters. While you should define the types and parameters for your function, you are not required to override this method.