Обсуждение: Client-Side triggers possible?

Hi,

Is there any way to get clients notified about data-changes without polling?

What I would need would be a client-side equivalent to triggers, e.g.
if one client inserts into a table all other interrested clients
should somehow get notified.

Thank you in advance, Clemens

Clemens Eisserer <linuxhippy@gmail.com> wrote:

> Is there any way to get clients notified about data-changes
> without polling?
>
> What I would need would be a client-side equivalent to triggers,
> e.g. if one client inserts into a table all other interrested
> clients should somehow get notified.

If you funnel all access through a client-side framework, yes you
can do that.  This, however, has very little to do with the database
which lies behind such a framework -- so a list for a particular
database product may not be the best place to ask this question.

Be warned that incoming programmers will tend to feel constrained by
having to go through your framework rather than using their favorite
tools and techniques.  Don't try this unless you have managers who
are willing to hold the line on this.  For that matter, make sure
that the benefits outweigh the disadvantages -- there are trade offs
here.

-Kevin

Micka wrote:
> you should take a look at that :
>
> http://jdbc.postgresql.org/documentation/83/listennotify.html

I wonder why you didn't suggest
http://jdbc.postgresql.org/documentation/head/listennotify.html

Isn't it best to give links to the /current/ docs?

(And not to top-post?)

--
Lew
Ceci n'est pas une pipe.

Hi,

> you should take a look at that :
> http://jdbc.postgresql.org/documentation/83/listennotify.html

Thanks that was exactly what I was looking for :)
Unfourtunatly there's still polling required, it seems the jdbc driver
has to issue requests in order to get the notifications.

> If you funnel all access through a client-side framework, yes you
> can do that.  This, however, has very little to do with the database
> which lies behind such a framework -- so a list for a particular
> database product may not be the best place to ask this question.

Listen/Notify was what I was looking for, and it is provided by
postgresql and its jdbc driver, so I couldn't have asked at a better
place.

I "only" need this for a university project where we have to solve the
same solution one time with a tuple spaced middleware and one time
using convetional technologies like RMI or databases.
I wouldn't go down that router otherwise ;)

Thanks a lot, Clemens

Micka wrote:
> you should take a look at that :
http://jdbc.postgresql.org/documentation/head/listennotify.html

which tells us
> A key limitation of the JDBC driver is that it cannot receive
> asynchronous notifications and must poll the backend to check
> if any notifications were issued.

thus not fulfilling the OP's criterion that there be no polling:

Clemens Eisserer wrote:
>> Is there any way to get clients notified about data-changes
>> without polling?
>>
>> What I would need would be a client-side equivalent to triggers,
>> e.g. [sic] if one client inserts into a table all other interrested
>> clients should somehow get notified.

--
Lew
Ceci n'est pas une pipe.

On 12/28/2010 02:27 AM, Clemens Eisserer wrote:
> Hi,
>
>> you should take a look at that :
>> http://jdbc.postgresql.org/documentation/83/listennotify.html
>
> Thanks that was exactly what I was looking for :)
> Unfourtunatly there's still polling required, it seems the jdbc driver
> has to issue requests in order to get the notifications.

Actually, in newer versions it doesn't have to poll the server. You can
test to see if there are notifications ready to receive and process them
on a timer loop. You're still polling, but only locally within the JVM;
you're not creating any new network activity.

This does *NOT* work if you're using an SSL socket, though, so you have
to be prepared to fall back to issuing "SELECT 1;" or the like for
server-side polling if you can't use client-side-only polling.

--
Craig Ringer