improve method seekBlock

[jasonwee]

TODO if big loop over big file pointer, may not be efficient, consider jump to the nearest file block. https://github.com/Opentracker/luceneOnCassandra/blob/master/src/main/java/org/apache/lucene/cassandra/FileDescriptorUtils.java

long jumpBlocksSize = 0;

long newWhichBlock = filePointer / descriptor.getBlockSize();  
if ( newWhichBlock > 0) {
        System.out.println("using new seek");
        int start = (int) --newWhichBlock;
        jumpBlocksSize = descriptor.getBlockSize() * start;
        System.out.println("start " + start + " jumpBlocksSize " + jumpBlocksSize);
        for (int i = start; i <= descriptor.getBlocks().size(); i++) {
            System.out.println("loop " + i);
            FileBlock fb = descriptor.getBlocks().get(i);
            jumpBlocksSize += fb.getDataLength();
            if (filePointer < jumpBlocksSize) {
                fb.setBlockOffset(jumpBlocksSize - fb.getDataLength());
                fb.setDataPosition((int) (filePointer - fb.getBlockOffset()));
                System.out.println("hit and return block " + fb.getBlockNumber());
                return fb;
            }
    }
}