Iterating a ResultSet using the JDBC for Oracle takes a lot of time about 16s?

Question

while( result_set.next() )
{
  ...
}

I have use System.nanoTime() and calculated the time, for each iteration the time taken is in mil

Answer 1

Try to change ResultSet fetch size. By default, Oracle JDBC driver receives the result set only 10 rows at a time from the database cursor. It may not significantly improve performance but there arent many other options to make driver work faster.

Answer 2

I have set up a table with 4000 rows and 10 columns with 10 characters each and made a simple performance test using the following approach (RealTimeCounter is a class which measures the real time between start() and stop()):

List<String> myResult = new ArrayList<>();
ResultSet rs = s.executeQuery("SELECT * FROM Performance");

RealTimeCounter rtc = new RealTimeCounter();
rtc.start();
while(rs.next()) {
    myResult.add(rs.getString(1));
}
rtc.stop();
System.out.println(rtc);

Results:

• Default fetch size: execution time is approx. 20 sec
• fetch size = 100: execution time is approx 2.2 sec
• fetch size = 500: execution time is approx 450 msec
• fetch size = 2000: execution time is approx 120 msec
• fetch size = 4000: execution time is approx 50 msec
• fetch size = 4001: execution time is approx 10 msec (!!)

So, the fetch size does have a significant impact on the execution speed.

---

Note that, on the other hand, the fetch size has some impact on memory consumption. Interestingly enough, a quick analysis using Runtime.getRuntime().freeMemory(); before and after the above code showed that the impact is much less than I would expect, though. The numbers I got are:

• Default fetch size: 665k
• fetch size = 100: 665k
• fetch size = 500: 665k
• fetch size = 2000: 743k
• fetch size = 4000: 821k
• fetch size = 4001: 861k