Functions that return collections of rows are known as table functions. They can be used like database tables in the FROM clause of a query or in the SELECT list of a query as a column name.
A regular table function creates an entire collection before returning it to the requesting query. But the performance of table functions can be improved by the implementation of pipelining and parallelization, giving the following benefits:
- Pipelining allows rows to be passed out of table functions as they are produced, rather than waiting for whole collections to be produced before the results are returned. The outcome is a reduction in the time taken for the first rows to be produced and a reduction in the total amount of memory consumed by the table function.
- Parallel enabling table functions allows their workload to be split between multiple slave processes, which may result in faster execution.
