On Wed, Jun 20, 2018 at 1:02 PM, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote:
> On 2018-Jun-20, Igor Korot wrote: > > > [quote] > > In order to create an event trigger, you must first create a function > > with the special return type event_trigger. This function need not > > (and may not) return a value; the return type serves merely as a > > signal that the function is to be invoked as an event trigger. > > [/quote] > > > > So, the function has to be created and compiled. > The section talking about C-language event triggers leads with: """ This section describes the low-level details of the interface to an event trigger function. This information is only needed when writing event trigger functions in C. If you are using a higher-level language then these details are handled for you. In most cases you should consider using a procedural language before writing your event triggers in C. The documentation of each procedural language explains how to write an event trigger in that language. """ In short, I agree that cursory reading of the main event trigger chapter could lead one to conclude that they are implemented in "C"; but all of the relevant information is available in the docs and correctly pointed too and accessible if one reads carefully or looks for it explicitly. I don't see how it can be much improved simply and there doesn't seem to be enough confusion (or use) to warrant significant effort in that area. > Event trigger functions can be written in plpgsql. You can use > pg_event_trigger_ddl_commands() in the ddl_command_end event to obtain a > few tidbits about the DDL that was just executed. > There are a number of examples of a pl/pgsql function returning an "event_trigger" pseudo-type: but I cannot locate an official statement that doing so is valid. I was expecting a paragraph at [1] but it is not there. Adding one and linking it to the overall event trigger chapter as well as the event trigger section of the pl/pgsql chapter seems warranted. [1] https://www.postgresql.org/docs/10/static/plpgsql-overview.html#PLPGSQL-ARGS-RESULTS David J.
