Hello Brad,
I don't have a good solution for you, but a few suggestions.
Is checking if there are any active transactions good enough?
This can by done by querying syscs_diag.transaction_table.
If there are no transactions, can you freeze the database (stops
updates, not selects I believe) or just take down the network server?
The update could then be made by reconnecting from the update tool with
the embedded driver. When done, bring the network server back up.
Far from perfect, but will it do for you?
Another option is taking exclusive locks on "crucial" tables in your
application, but this might not be feasible with your application.
Further, I don't know how well your clients handle connection failures
or timeouts/deadlocks.
If not nothing of the above is helpful, and nobody else chimes in with
suggestions, I think you have to go for an application specific solution
and/or file a feature request in Jira. Getting the current connection
count sounds like a useful feature.
(https://issues.apache.org/jira/browse/DERBY)
In the scenario of getting info from/about the server, would JMX be an
option for you?
--
Kristian
Brad Moore wrote:
Thanks for your response. I think I need to clarify a couple of things
though.
We are not using Access as the front end, we were using it for the
database and now that has been converted to Derby. The front end is
written in another language that can connect to the database using ODBC
or JDBC. Moving to Postgre now is not possible with the timelines that
we have, and the fact that the conversion to Derby is nearly completed now.
Unfortunately the way our program works I can not just upgrade the
database behind the scenes without our users being aware of it. Our
program is a product that we sell and our clients install on their
servers and client machines. I do not have access to their computers to
do the database upgrades. We use a third party installer app that we
can create scripts in to perform the upgrades (Indigo Rose TrueUpdate).
TrueUpdate is able to check a script on our web server to determine if
there is an upgrade available. If there is an upgrade available it
informs the user and asks them if they want to upgrade or not. If they
choose to upgrade then it runs our scripts which includes upgrading the
database as well as the front end application.
The main reason I need to ensure that everyone is out of the database
while the database upgrade is being performed is because I could be
adding/dropping columns or tables in the upgrade and I don't want the
previous version's front end application accessing a partly or fully
upgraded database. If all of the users are disconnected from the
database while the database upgrade is performed then the next time they
try to connect to the database the application checks to make sure that
the front end application version matches the back end database version,
and if it doesn't it forces them to upgrade their front end application
so that the front end and back end is always in sync.
This has worked very well for us for several years using this method
with the Access database, but I don't know how to ensure that all of the
users our logged out of the Derby database. I'm starting to think I may
have to add a table to the database that tracks who has logged in and
when, and when they have logged out. There could be issues with this
however, where if the user shuts down their computer without logging out
of the application the table would still have a record in it saying that
they are currently logged in when they are not.
Any other suggestions?
Thanks,
Brad
> From: [EMAIL PROTECTED]
> To: derby-user@db.apache.org
> Subject: Re: Methods for upgrading database and application
> Date: Tue, 12 Feb 2008 12:23:53 +0200
>
>
>
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> ----- Original Message -----
> From: Brad Moore
> To: Derby Discussion
> Sent: Tuesday, February 12, 2008 2:51 AM
> Subject: Methods for upgrading database and application
>
>
> Hi,
>
> I am currently working on converting our client/server application
from an
> MS Access database to using Derby. We have approximately 40 sites
that use
> our software and each one can have from 1 to 10 client computers that
> connect to the central database.
>
> The latest issue I have come across is how to handle the application and
> database upgrades at our client sites.
>
> Our current process is automated and works like this:
> 1. Check on our website to see if there is a new release available
> 2. If there is a new release available, download the new client
> application and the scripts to upgrade the database
> 3. Determine if anyone is currently connected to the database prior to
> performing the upgrade so we are not altering tables while someone is
doing
> work.
> 4. If anyone is connected to the database we abort the upgrade and
> inform the user that they should make sure all other users are
disconnected
> before performing the upgrade.
> 5. If there are no users connected to the database then we rename the
> Access file so that no users can connect to the database while we're
> performing the upgrade.
> 6. Perform the database upgrade.
> 7. Rename the Access database file back to it's original name so it is
> available for use again.
> 8. Upgrade the client application files.
>
> =======================================================
> Brad MS Access is the best prototyping tool in the world, and the worst
> database
> I vaguely remember writing tons of code to make it user friendly,
getting
> around exclusive locks
> and other stuff
>
> It sounds like a big system you have there, and I think you should
also look
> at big
> systems like Postgres
>
> I say this becaus I'm not sure of Derby's ODBC support, I dont know
if there
> is an official
> driver... and coming from MS I think you "better" make sure that
works well.
>
> On Postgres using MS Access as a frontend works, I not sure thats
Derby's
> thing....
>
> Coming from MS Access, I think you thinking small... on these big dB's
> things like worrying about
> users in the dB before you start routing maintenance... is done for you.
> Setting flags that say... when all the users are finished, lock down the
> dB... are just flags
>
> Also in most area's now the bigger dB's are MS friendly (Run Setup) but
> can also do linux
>
> Anyway
> Derby is a great dB... and its hard to classify them... but making an
> application that needs
> embedded dB (Derby is great), making an Accounting application where a
> networked dB
> just falls out of the JRE... Derby and Sun make it easy..
>
> Aim at sitting in your control tower... and just doing it all, no more
> download, and users banging their head.
> The user mustnt even know you in the dB and changing stuff...
> Running 10 branch offices.... do you homework is all I wanted to say....
>
> =======================================================
>
> Currently we are able to determine if anyone is connected to the Access
> database by just trying to rename the .mdb file. If this fails then the
> database is in use. I have been unable to find a good way to
determine if
> there are any users currently connected to the Derby database. I have
found
> mentions of calling NetworkServerControl runtimeinfo and looking at the
> Active Sessions, but I don't know of a way to call that function and
return
> the Active Sessions results to the installer program that I am using
(Indigo
> Rose TrueUpdate).
>
> Is there any other method for determining the number of users that are
> currently connected to a Derby database?
>
> Also, is there a way to lock the database so that no users can
connect to it
> while the upgrade is being performed?
>
> Is there anyone else that has a similar type of situation, and how
did you
> handle it?
>
>
> Thanks,
>
> Brad
>
