Multiple instances of an application using same embedded database?
Hi all- I am writing an application that uses embedded Derby for holding data that the application collects/creates. It works great, I really like Derby. But, there's a problem: multiple application instances. The application can be launched multiple times and each instance can potentially create and retrieve data that would be stored/queried from Derby. The problem is that the second instance fails to run correctly because the database is locked by the first instance of the application. I can't create a Derby server, the application must be zero-setup and zero-config; the application handles initial database creation, making the tables, etc. I've looked and there doesn't seem to be any info on this. Is this even possible? If not, might anyone know what I might be able to use? The original version of the program used SQLite, which keeps the database in the single file. This was nice, but there isn't a pure Java way to get at a SQLite db, and besides, I like the additional functionality Derby gives me. Thanks for any info, Tacho
Re: Multiple instances of an application using same embedded database?
Have a look at the archives of this list. It has been discussed already that you can use server mode similarly to embedded. Your application may try first use existing database as client and if fails to connect it may start server. Actually your second application instance would benefit from accessing as client because of derby server cache. On Fri, Jun 5, 2009 at 10:51 PM, Ron Olson tachokni...@gmail.com wrote: Hi all- I am writing an application that uses embedded Derby for holding data that the application collects/creates. It works great, I really like Derby. But, there's a problem: multiple application instances. The application can be launched multiple times and each instance can potentially create and retrieve data that would be stored/queried from Derby. The problem is that the second instance fails to run correctly because the database is locked by the first instance of the application. I can't create a Derby server, the application must be zero-setup and zero-config; the application handles initial database creation, making the tables, etc. I've looked and there doesn't seem to be any info on this. Is this even possible? If not, might anyone know what I might be able to use? The original version of the program used SQLite, which keeps the database in the single file. This was nice, but there isn't a pure Java way to get at a SQLite db, and besides, I like the additional functionality Derby gives me. Thanks for any info, Tacho
Re: Multiple instances of an application using same embedded database?
On Fri, 2009-06-05 at 22:58 +0200, Peter Ondruška wrote: Have a look at the archives of this list. It has been discussed already that you can use server mode similarly to embedded. Your application may try first use existing database as client and if fails to connect it may start server. Hi, I guess you could have the application try to connect using the embedded driver first, and if that fails it could assume another application instance has already booted the Derby database. In that case, the second instance could fall back to connect using the client driver (localhost, custom port maybe). There are multiple issues with this; - various race conditions to handle (pausing, retry) - the first instance to boot the database must start the server (doing this programatically is easy) - failover and retry logic for handling the case where the first application shuts down before the second instance - even though we try to keep the embedded and client driver fully compatible, there may be small differences between them - you could theoretically make your application instances talk to each other, such that you can request that a Derby server is started by the first instance Depending on the usage pattern of the application, this may get complicated... Is it a possibility to boot/create different databases, or does each instance require access to the same data (i.e. from earlier sessions)? Cheers, -- Kristian Actually your second application instance would benefit from accessing as client because of derby server cache. On Fri, Jun 5, 2009 at 10:51 PM, Ron Olson tachokni...@gmail.com wrote: Hi all- I am writing an application that uses embedded Derby for holding data that the application collects/creates. It works great, I really like Derby. But, there's a problem: multiple application instances. The application can be launched multiple times and each instance can potentially create and retrieve data that would be stored/queried from Derby. The problem is that the second instance fails to run correctly because the database is locked by the first instance of the application. I can't create a Derby server, the application must be zero-setup and zero-config; the application handles initial database creation, making the tables, etc. I've looked and there doesn't seem to be any info on this. Is this even possible? If not, might anyone know what I might be able to use? The original version of the program used SQLite, which keeps the database in the single file. This was nice, but there isn't a pure Java way to get at a SQLite db, and besides, I like the additional functionality Derby gives me. Thanks for any info, Tacho
