Can you have two connections to database

Question

I am running two java programs which access the same database. One runs forever, and keeps the same connection up. The other program, lets say does a simple update, but it stalls and will never do the update. If I kill the first programs connection, then the second program can do the update. I am using the jdbc thin client. Is there a way I can have these both run and not stall?

Answer 1

The short answer is, yes.
There are two general approaches to the problem. The first approach is to use various locking, commit and rollback techniques. The basic premise is that if program A runs into a problem, the database drops A and reverts back to the previous state before responding to program B. This is highly dependent upon the database you're actually using, and probably beyond the scope of this forum.
The second approach is to code your programs with a philosophy of "get in, do it, get out" as quickly as possible. In other words, do NOT leave a database connection open if you can avoid it.
Essentially your program makes a connection, does a select query, copies the results into a data structure you define, and exits. Then you're free to play with the results as you see fit. When the time comes to do an update, you make the connection, perform the update, then immediately exit. If you need to test it, make another connection, do a select on that record, copy it, close the connection, then compare the copy with what you anticipate.
There is the added benefit that whenever you close the connection, most databases will then do whatever commits need to be done, and release any deadlocks that may be in place.
Your problem isn't really that your database cannot do two connections - its the fact that your database does not want to let two separate people make changes to the same table at the same time. There's an obvious reason for it and we can go into more detail if you want.
But essentially, if you do each transaction as quickly as possible, and let the database clean up after each transaction, you will avoid most, if not all of the problems you're experiencing.
Don't worry about the overhead of creating and closing connections. If it does become a problem, you can always use a "Connection Pool" (search for it on the forums if you want to know more). You just don't want to be in a position where the database is saying "I can't give you the info you want because I don't know if this other program is going to change any of it before giving control back to me."