Parallel UDRs

The parallel database query (PDQ) feature executes a single query with multiple threads in parallel. Another feature, table fragmentation, allows you to store the parts of a table on different disks. PDQ delivers maximum performance benefits when the data that is being queried is in fragmented tables.

PDQ features allow the database server to distribute the work for one aspect of an SQL statement among several processors. For example, if an SQL statement requires a scan of several parts of a table that reside on different disks, multiple scans can occur simultaneously.

A PDQ is a query that the database server processes with PDQ techniques when the optimizer chooses parallel execution. When the database server processes a query with PDQ, it first divides the query into subplans. The database server then allocates the subplans to a number of threads that process the subplans in parallel. Because each subplan represents a smaller amount of processing time when compared to the original query and because each subplan is processed simultaneously with all other subplans, the database server can drastically reduce the time that is required to process the query.

For more information about the PDQ feature, refer to the HCL OneDB™ Administrator's Guide. For more information about the performance implications of PDQ, refer to the HCL OneDB Performance Guide.