The Query Capture Facility, or QCF, provides a method to capture and store the steps from any query plan in a set of predefined relational tables called the query capture database, or QCD.
You create your QCD databases using the procedures described in Sizing a Query Capture Database .
QCD Information Source
The principal source of the captured information in QCD is the white tree produced by the Optimizer, the same data structure used to produce EXPLAIN reports (the current implementation of QCD does not represent all the information reported by EXPLAIN). The white tree represents the output of the final stage of optimization performed by the Optimizer.
QCD Physical Model
In the physical implementation of QCD databases, text columns that may contain names are explicitly defined as Unicode for proper handling of any Teradata-supported character set.
The table SeqNumber feeds the values of the artificial sequential number columns defined for QCD attributes.
See Query Capture Database for information about physical capacity planning for your QCDs.
Applications of QCF and QCD
- QCD can store all query plans for customer queries. You can then compare and contrast queries as a function of software release, hardware platform, and hardware configuration.
- You can generate detailed analyses of captured query steps using standard SQL DML statements and third party query management tools by asking such questions as the following:
- "How many spool files does this query use?"
- "Did this query plan use a product join?"
- "How many of the steps performed by this query were done in parallel?"