Flavio Palumbo wrote:
Hi Stanley,
thanks for your responses ;-))
I looked the links you provided but I think my scenario is different.
I still don't quite understand the scenario.
Let's say there are 3 workstations (A, B and C) and one server (X).
I think you have a directory/disk on X that is shared between all
workstations.
If you want to access a shared database from A, B and C at the same
time, the most common solution would be to start the Derby network
server on X, and have the applications on the workstations connect with
the client driver (org.apache.derby.jdbc.ClientDriver).
This would require some management of server X, including
starting/stopping the Derby network server when the machine is
started/shutdown. The Derby network server would always be running as
long as X is running.
*If* Derby were able to operate efficiently and correct when the
database files are stored on a network drive, you would have to handle
the logic of determining if and where the Derby network server is
started. Doing this might require knowledge of all possible clients, a
well-known location to post this information, or maybe a peer-to-peer
architecture.
Maybe I'm a bit dense, but can you please explain why the centralized
server approach won't work for you?
I wrote a stand alone application (like a VB .exe, not WEB) that is shared
on a local network because the directory where the jars resides is shared
for all the network users ; inside this directory is defined a derby
database with 2 user tables, and I'd like that the access to these tables
was shared for all the users that concurrently run the application.
The first time I tried to use the embedded driver, but this way doesn't
share the database ; thus I tried to implement the network server making it
start every time a user starts the application but in this way I found the
problem mentioned in earlier mails.
I think a right way could be start the server once, in a separate jvm, when
the first time the application is called and then let it up and running
until the PC is shut down.
What you think about this ??
Here I'm confused again. Do you want to share data between multiple
machines, or only between multiple applications on a single machine?
Another problem is that I don't know how start the server from inside the
application in a separate jvm.
Could you give some other hints or code snippet ??
You could check if you can connect on specified port. If not, you assume
the server is down, and that you are responsible for starting it. I'm
sure someone know how to start the server as a separate process/JVM, but
let us first make sure that is what you want to do :)
Regards,
--
Kristian
Thanks a lot
Flavio
-----Messaggio originale-----
Da: Stanley Bradbury [mailto:[EMAIL PROTECTED]
Inviato: lunedì 31 luglio 2006 21.15
A: Derby Discussion
Oggetto: Re: R: connection strange behavior
Flavio Palumbo wrote:
Hi all,
sorry for the long delay of this response but I spent a little
holiday ;-))
Could you please provide some code examples ?? specially when you say :
"Usually it is done by defining a global datasource that is started when
the server starts. Then by setting the property
derby.drda.startNetworkServer to true in the JVM arguments that are set
at Server startup the Network Server will also start. It is recommended
that he Network Server be started and shutdown when the server starts
and shutdowns and also that a security manager be used to secure the
environment."
Thanks a lot.
Flavio
Flavio Palumbo wrote:
Hi,
thanks everybody for the suggestions provided ;-))
Now I try to explane my goal :
- I have an application shared in a local network environment (one jar
file
where every client in the network can double
click and start it in a new jvm)
- when the application starts, I'd like to start
(automatically) the derby
network server
- every client opens a new connection to the server
- when the client finishes its work, it closes its own connection, shut
down
its instance of the application and closes
its jvm
- the last client closes the server
- note that the shared derby DB is in a network shared directory
to achieve the aim explaned above I wrote a test case where I
do something
different : every time the application starts,
it starts a new instance of the network server and a new
connection. I did
this cause I don't know how to start the network server only once (when
the
first client starts the application) and also don't know how to be
informed
when the last
client closes the application.
This kind of test seems to work ; if I open the application in two
different
shells of my PC (two jvm) I can read and write into the same
table of the
same db, thus it seems to be shared as I desire.
But following the tests I encountered some impredictable errors (not
always
the same error, data seems to be lost, strange exceptions ...)
making me
think maybe this is not the right way :-((
Thanks for any suggestion
Flavio
=== SNIP ========
Hi -
Ouch, You are correct when you say:
" (not always the same error, data seems to be lost, strange exceptions
...) making me think maybe this is not the right way "
Strange exceptions and data loss is what happens when database I/O is
performed across a network. Your configuration is causing
these problems:
" - note that the shared derby DB is in a network shared directory "
The disks must be local to the machine running the Derby engine.
A centralized server architecture will handle this. Start your server
and the Network server on the machine where the database files reside
and have the applications connect either to the server via whatever
protocols it supports or via the Network Server using the client
driver. How you set this up depend on the server you are using.
Usually it is done by defining a global datasource that is started when
the server starts. Then by setting the property
derby.drda.startNetworkServer to true in the JVM arguments that are set
at Server startup the Network Server will also start. It is recommended
that he Network Server be started and shutdown when the server starts
and shutdowns and also that a security manager be used to secure the
environment.
HTH
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I'm not sure of the architecture you are using. My response assumed
that you were using an Application Server like Geronimo, Tomcat , etc.
These each have their own methods for defining Global datasources. You
can find writeups that contain instructions on doing this under 'Product
Writeups' on the Apache Derby Resources page:
http://db.apache.org/derby/integrate/index.html#products
If you are writing your own Server and want to add datasource
functionality to it you might want to use the system that Tomcat uses:
|commons-dbcp| (http://jakarta.apache.org/commons/dbcp/).
Is this what you needed ??
-----------------------------------------------------------
Il presente messaggio non costituisce un impegno contrattuale tra SILMA S.r.l.
ed il destinatario.
Le opinioni ivi espresse sono quelle dell'autore.
SILMA S.r.l. non assume alcuna responsabilita riguardo al contenuto del
presente messaggio.
Il messaggio è destinato esclusivamente al destinatario.
Il contenuto e gli allegati sono da considerarsi di natura confidenziale
Nel caso abbiate ricevuto il presente messaggio per errore siete pregati di
comunicarlo
alla casella [EMAIL PROTECTED]
