backing up a db, jdbc, SQL syntax, etc...

Hello together!

I come up with a conglomerat of questions ;-)

o What do you think is the best way to backup the data stored in a
postgres db? Backing up the whole db-file, doing a dump into ascii files with
seperators or whater ever method else?

o Is there a maximum number of connections to the backend that could
run us into trouble if lot's of users who are connected via jdbc do not
close their applets?

o Do I have to take any speacial locking mechanism in SQL into account
for a high number (~500) of users. I only use SELECTs, UPDATEs, INSERTs and
NEXTVALUE from a sequence over jdbc. Problems with caches, memory/connection
...?

o Does anyone know how I can throw out (stop) a java applet completly out of the
java interpreter in a browser; so that all resources and memory are released.
In the moment this only happens when I kill the browser (netscape on linux)

Here some Q's which I posted some times ago in the novice-list but where
not answered and so are still open (for me, naturally :-) )

o Where is the difference between:

SELECT f.title, f.did, d.name FROM dist d, films f WHERE f.did=d.did;
and
SELECT films.title, films.did, dist.name FROM dist JOIN films
USING(did);

or a formulation with inner join? Don't the result in the same output?

If I'm not mistaken, why do I get a inner join not yet implemented
information, would a inner join have to be implemented in a different
way in the db-backend?

Greetings from Austria,

Georg Ritter

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student at department of physics
University of Innsbruck, Austria Georg(dot)Ritter(at)uibk(dot)ac(dot)at