[SQL] concurrency problem

[sathish kumar shanmugavelu]

Dear group,
    Let me explain my issue.
       We use
              Database      - postgresql-8.1
              JDBC Driver  - postgresql-8.1-407.jdbc3.jar
              Java             - jdk1.5
              The default transaction isolation level is - Read Committed
              Auto Commit is false
    In our application we used a single connection object. We open the connection in the MDI form and close it only when the MDI closes , simply when the application closes.
    I give a insert statment like
             INSERT INTO rcp_patient_visit_monitor (
                   entry_no, patient_id, visit_date, is_newpatient, visit_type, is_medical,
                   is_review, is_labtest, is_scan, is_scopy, is_xray, weight, height)
                   VALUES ((SELECT coalesce(max(entry_no)+1, 1) FROM rcp_patient_visit_monitor),?,current_timestamp,?,?,?,?,?,?,?,?,?,?)
      
    The point to note here is the select statement which gets the max entry_no and adds one to it and save the new value. entry_no is the primary key of the above table.
   
   Now i run the same program (different instance) from two systems, save the form simultaneously, only one entry is saved, in the other system the error says - duplicate key violates.

   If i use the transaction level - Serializable - again one entry is saved. Only on closing this application (closing the connection) the application running in other system is getting saved.
 
   If i lock the table and create a transaction - by sending the commands
         con.createStatement().executeUpdate("begin");
         con.createStatement().executeUpdate("lock table rcp_patient_visit_monitor");
         int rows = psSave.executeUpdate();
         con.createStatement().executeUpdate("commit");
  
   The form in one system is saved, in another system an error says - ' Deadlock detected  .....'
  
    When i test the above said commands in dbvisualizer from two different systems , it works, but here it does not. why.
  
    how to solve this concurrency problem.

Thanks in advance,
--
Sathish Kumar.S
SpireTEK