Dear StackOverflowers,
I am in the process of writing an application that sorts a huge amount of integers from a binary file. I need to do it as quickly as possible and the main performance issue is the disk access time, since I make a multitude of reads it slows down the algorithm quite significantly.
The standard way of doing this would be to fill ~50% of the available memory with a buffered object of some sort (BufferedInputStream etc) then transfer the integers from the buffered object into an array of integers (which takes up the rest of free space) and sort the integers in the array. Save the sorted block back to disk, repeat the procedure until the whole file is split into sorted blocks and then merge the blocks together.
The strategy for sorting the blocks utilises only 50% of the memory available since the data is essentially duplicated (50% for the cache and 50% for the array while they store the same data).
I am hoping that I can optimise this phase of the algorithm (sorting the blocks) by writing my own buffered class that allows caching data straight into an int array, so that the array could take up all of the free space not just 50% of it, this would reduce the number of disk accesses in this phase by a factor of 2. The thing is I am not sure where to start.
EDIT:
Essentially I would like to find a way to fill up an array of integers by executing only one read on the file. Another constraint is the array has to use most of the free memory.
If any of the statements I made are wrong or at least seem to be please correct me,
any help appreciated,
Regards
You might want to look into the Java NIO libraries, specifically File Channels and Int Buffers.