External (asynchronous) notifications of database updates

Hi List,

I have a(n external) system driven by data in a Postgres database. I am
looking for a functionality, which would asynchronously inform the
system of any updates into the database, so the system could reflect the
updates (without having to poll the database at regular basis).

I have been skimming through various Postres' replication tools,
becasuce replication needs the same functionality in general. All the
tools I've found are based on, yes, triggers. But I don't know how to
cope with transactions - strictly speaking with rollbacks:

As a row-level 'after insert/update/delete' trigger can create
an external notification of the change, it will not see the reverse
change if the current transaction is later rolled back.

I don't know how the various replication tools solve this - do you?

Thanks in advance for any piece of information, now I choose a terrible
hack - when I get a notification, I wait for 10 seconds and then read
the whole table... It works for me now, but might not work tomorrow.

Milan