Java - DB2 性能改进

Question

We have a SELECT statement which will take approx. 3 secs to execute. We are calling this DB2 query inside a nested While loop.

Ex:

While(hashmap1.hasNext()){ while(hashmap2.hasNext()){ SQL Query } }

Problem is, the outer While loop will execute approx. 1200 times and inner While loop will execute 200 times. Which means the SQL will be called 1200*200 = 240,000 times. Approx. each iteration of Outer While loop will take 150 secs. So, 1200 * 150 secs = 50 hrs.

We can afford only around 12-15hrs of time, before we kick off the next process.

Is there any way to do this process quickly? Any new technology which can help us in fetching these records faster from DB2.

Any help would be highly appreciated.

Note: We already looked into all possible ways to cut down the no.of iterations.

Answer 1

Sounds to me like you're trying to use the middle tier for something that the database itself is better suited for. It's a classic "N+1" query problem.

I'd rewrite this logic to execute entirely on the database as a properly indexed JOIN. That'll not only cut down on all that network back and forth, but it'll bring the database optimizer to bear and save you the expense of bringing all that data to the middle tier for processing.