PreparedStatement Synchronization Query

Question

Hi All,
I hope this is the right place to post this query (heh)! In a Java Webapp I have around 30 PreparedStatement(s) stored as global variables. As it is possible that some of the PreparedStatement(s) will be executed by multiple users concurrently from different pages (i.e. sections of the code), in addition to the usual synchronization tags I have volatile boolean values to check whether a PreparedStatement is currently in use to prevent concurrent execution. For example:
//  PreparedStatement is global, ResultSet is local.
synchronized(this) {
  while (flagRaised) {
     try {
       wait();
     } catch (InterruptedException e) {
       // do nothing.
   flagRaised = true;
   try {
     preparedStatement.setString(1, "Pears");
     localResultSet = preparedStatement.executeQuery();
   } catch (SQLException e) {
     // log the problem
   flagRaised = false;
   notifyAll();
}I believe that this is necessary for any "mutator" statements where I'm using "setXXXX", but if I had a statement that returned an entire table would I need to implement any additional synchronization code? For example could I simply have:
localResultSet = preparedStatement.executeQuery(); // where the PreparedStatement returns a table.with no synchronization/volatile variables?
Thanks in anticipation,
Simon

Answer 1

I fail to see why the above is necessary. Think of what you are doing: caching a PreparedStatement. Why?
PreparedStatement, out of the box with a decent JDBC driver, will cache the parsed SQL query. Further, most RDBMS will also perform their own native cachine of query plans. (I will leave out the considerations of RDBMS cached execution plans, though they are also valid to the discussion). You are adding a level of pooling above and beyond what the vendor offers. This might be necessary if your own system, but have you benchmarked this? Do you 'know' the middleware parse of a PreparedStatement is your actual scaling bottleheck. IMO, this is a rare situation.
Rather, understand what both your RDBMS and your JDBC driver's use of PreparedStatement already offer you. Premature optimization is the root of most software evil, at least according to Knuth. Sure you are not contributing to the same?
- Saish