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Re: Some questions on GSOC project User Defined Event


Hi, Savita!

On Mar 08, Savita Agrawal wrote:
> what is the difference between a trigger and user defined event?

A main difference: a trigger is automatially run by DBMS when something
happens. User defined event - you need to wait for it, it's more
procedural programming.

> In postgres there is a clear distintion between trigger and event
> trigger. Triggers are activated when DML statements are executed whereas
> event triggers are activated when DDL statements are executed.

No, that's unrelated.

> But in soliddb (from which our post in JIRA page is inspired), it
> seems like user defined events can be activated for DML statements.
> What is it that can't be done with triggers and can be done with user
> defined event?

Waiting for something to happen. You cannot wait with a trigger.

> Why is the restriction that events can only be posted and received by
> stored procedures only?

I'd say, events can be posted from anywhere, not only a stored
procedure. But received - yes, only there, because we don't support
compund statements outside of a stored routine yet.