PostgreSQL 8.3 introduced a couple of new features that improves the processing of functions and makes plpgsql
functions easier to write. These are as follows:
- The new ROWS and COST declarations for a function. These can be used for any PostgreSQL function written in any language. These declarations
allow the function designer to dictate to the planner how many records to expect and provide a hint as to how expensive a function call is. COST is measured in CPU cycles. A higher COST number means more costly.
For example a high cost function called in an AND where condition will not be called
if any of the less costly functions result in a false evaluation. The number of ROWs as well as COST will give the planner a better idea of
which strategy to use.
- RETURN QUERY functionality was introduced as well and only applies to plpgsql written functions.
This is both an easier as well as a more efficient way of returning query results in plpgsql functions.
Hubert Lubazeuwski provides an example of this in set returning functions in 8.3.
We shall provide yet another example of this.
- Server configuration parameters can now be set on a per-function basis. This is useful say in cases where you know a function will need a lot of work_mem, but you don't want to
give all queries accessing the database that greater level of worker memory or you are doing something that index scan just works much better than sequential scan and you want to
change the planners default behavior only for this function.
- Scrollable Cursors in PL/pgSQL - this is documented in Declaring Cursor Variables
- Plan Invalidation - Merlin Moncure covers this in PostgreSQL 8.3 Features: Plan Invalidation so we won't bother giving
another example of this. Basic point to take away from this is that in procedures where you have stale plans floating dependent on tables being dropped by a function, those plans will
be automagically deleted so you don't have ghost plans breaking your function.
