使用多个数据库连接会导致死锁

Question

To resolve the issue mentioned here .

We are creating and using 2 same JDBC Singleton Connections(Regular, Proxy).

• But by doing so we are facing deadlock when we try to use both connections consecutively on same table for doing multiple inserts and updates.
• When this happens, I cannot run any queries from the DB tool (Aqua Data Studio) as well.
• My assumption is that it waits indefinitely for other connection to release lock.

Note: We are not dealing with multi-threading here.

Issue:

//  Auto Commit false
// Singelton
Connection connection = getConnection();  //same        

// Auto Commit true
// // Singelton
Connection proxyConnection= getConnection();  //same

PreparedStatement ps = null;

try{
   connection.setAutoCommit(false);

   //Step 1
   String sql = getQuery(); 
   ps = proxyConnection.prepareStatement(sql); 
   ps.executeUpdate();        
   .
   .
   //Step 2
   // if I don't execute this step everything works fine.  
   sql = getTransctionQuery();              
   ps = connection.prepareStatement(sql); 
   ps.executeUpdate();   

   .
   .
   //Step 3
   sql = getQuery(); 
   ps = proxyConnection.prepareStatement(sql);  
   ps.executeUpdate();  // this line never completes (if Step 2 runs)

}catch(){
   connection.rollback(); //Doesn’t rollback step 1 and understandably step 2.
}
finally{
   connection.close();  //cleanup code
   proxyConnection.close();
}

Question:

• How to resolve this issue?
• How to make sure different connections, though they are creating using same class loader, won't lock database/table.

Thanks

Answer 1

I'm no expert here but I used to have problems with Oracle DB when running a query and then forgetting to commit (or cancel). So I think that the fact that you didn't commit after step 2 locks the database for the next access.