Wednesday, 21 December 2016

Laws in Physics vs. in Computer Science

The laws of physics and nature are unchanged and we just have to discover them. It requires a lot of imagination and thorough study to fully explain and prove a law. A beautiful and rewarding effect is that later on we can predict certain phenomenon or simply what will happen next based on the laws. An example is the Fermat law that says that light always traverses the path that gives it the lowest running time. You can, for example, infer that because the atmosphere is denser than the vacuum, the light that comes to your eye from the Sun is curved and in reality when you watch a sunset, the Sun is already below the horizon, even though it is still visible.

On the other hand, there are no true and unchanged laws in computer science. The design of systems changes and the way it does can be surprising as every designer/human being has different preferences and can even change a commonly accepted "good design choices". An example is a mismatch between OS page size and DBMS page size, 4 KB and 8 KB respectively. The database can fetch 8 KB pages randomly, for example, because of the index-based scan. On the other hand, the OS notices that the application (DBMS in this case) starts from fetching 2 pages in a row (2x OS page of 4 KB - gives the 8 KB page fetched by the DBMS) and OS assumes that it must be a sequential scan of pages, so it additionally prefetches another 2x 4 KB pages (16 KB in total), the second 8 KBs in vain. The other 2 pages won't be read subsequently. Afterwards, DBMS goes to a totally different location to fetch another 8KB page.

The systems could have a built-in level of adjustment (probably built-in Machine Learning components) that could simulate the nature and automatically improve as the time progresses, for example changing the number of pages to 3 in a row to trigger sequential scan assumption in the OS. The computer environment should imitate better the natural environment.

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