how can i check bottle neck in my code while node is running?

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Finding bottlenecks in code is called Profiling and is interesting in many fields. There are many tools to do it, but none which work fairly automatically - they all require some fiddling with, so they are not necessarily _easier_ to do than printing current time and working backward, but they likely will tell you more. Perhaps you can use http://wiki.ros.org/roslaunch/Tutoria... as a start, and continue to search for tutorials on how to use tools like gprof to make your code high performant.

That said, accumulating 800 3D points into an (ever growing) storage 200 times per second sounds like a very compute heavy process. In particular, arrays can typically not be resized in any performant way. If you think you resize an array, it is more likely that you allocate another array of the new size and copy all data from the latest iteration into there. Copying data, by the way, is a very expensive process as well. I don't think you should expect to get all 200 scans accumulated every second.

So, what can be done in this situation? Think about your problem for a moment - what are you trying to do? Do you actually need 800 points in every scan? Perhaps some filtering can be done to reduce that number? Do you need 200 scans per second, or could you make a sufficiently good image with 100 or 50 scans? What about the accumulation - could you pre-allocate the memory that you need so that you don't have to resize arrays when live? Can this process be parallelized? Is ROS the right network of choice here, or can you get a faster connection by editing the source code to the driver? There are many avenues to explore, and I hope you find a good solution for your problem.