On Feb 5, 2009, at 6:08 AM, Greg Stark wrote:
On Wed, Feb 4, 2009 at 6:42 PM, Simon Riggs <simon@xxxxxxxxxxxxxxx>
wrote:
As A.M. says elsewhere, it would be good to have a trigger that
fired a
NOTIFY that was picked up by a scheduled job that LISTENs every 10
minutes for certain events.
We need a place for code that is *not* directly initiated by a user's
actions, yet works as part of a closed loop system.
Can't you do this today in about three lines of your favourite
scripting language?
I used to do this in perl on Oracle and that was without anything like
LISTEN/NOTIFY to optimize it. Web pages just inserted a record and
went on about their business while a worker daemon scanned for new
records and generated notification mails.
The problem with trying to push everything into the database is that
it ends up sucking your entire application into the database. That
limits your choice of languages and tools, and also creates a huge
bottleneck.
In addition to the other response, one should also take security
scenarios into consideration. If role X installs an event handler
(timed or via notify), I would expect the callback to be run as that
role X. This is currently impossible to safely do from outside the
database because SET SESSION AUTHORIZATION can be trivially revoked
with RESET SESSION AUTHORIZATION. Also, LISTEN/NOTIFY really need to
allow for additional user info to be attached (it's on the TODO list)
and they have further security problems because they are global
broadcasts. I would expect an integrated event dispatch mechanism to
handle the complexity of security as well as what to do in case of
rollback.
So, no, this is not something can be slapped together from outside the
db.
Cheers,
M
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