When a message comes in to the master index application, values from the message are used as criteria for the blocking query used for matching. Several queries are created depending on the number of blocks that are defined. If the incoming message contains common default values, the query could result in an inordinate number of possible matches being returned from the master index database for the match process. You can reduce this overhead by excluding known invalid values from blocking query fields, thereby reducing the number of non-matching query results.
As an example, a blocking filter for the Phone field excludes the value “9999999999” and the blocking query contains a block on the FirstName and Phone fields. If an incoming record contains “9999999999” in the Phone field, the blocking query returns no matching records for that specific block of the query. Note that records containing the excluded value might be returned by other blocks in the query that do not include the Phone field.