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Is it best practice to layout data with normalisation?

Discussion in 'Data Oriented Technology Stack' started by TMPxyz, Jul 14, 2019.

  1. TMPxyz

    TMPxyz

    Joined:
    Jul 20, 2012
    Posts:
    765
    I'm asking this question coz when reading the "Data-Oriented Design" book, it claims we should layout the data like in relational database and do normalisations.

    Now, if we only talk about the basic 1NF, which means every field of the data struct should have one and only one element (No NULL, No List). This clearly goes against the use of DynamicBuffer.

    1NF looks great for cache at first glance, but it seems to cause many other troubles elsewhere.

    For example: let's compare two schemes of data layout for representing a directed-graph:

    Non-1NF ( use list ): Every node is an Entity, and the node has links in dynamic buffer
    Code (CSharp):
    1. class N_Link{
    2.      float link_cost;
    3.      Entity to_node;
    4. }
    5.  
    6. class N_Node{
    7.      float node_cost;
    8.      List<N_Link> links; // <-- should be DynamicBuffer here, write List for simplicity
    9. }
    1NF (no list): Every Node & Link are Entity.
    Code (CSharp):
    1. class Link{
    2.      float link_cost;
    3.      Entity from_node;
    4.      Entity to_node;
    5. }
    6.  
    7. class Node{
    8.     float node_cost;
    9. }
    It's clear that with 1NF we could have more compact mem layout, but it would be troublesome if we want to find out all the links of a given node without auxiliary data struct like Dictionary.

    So, do you guys think it's a best practice to layout data like database? I'm kinda doubtful here.
     
  2. Ashkan_gc

    Ashkan_gc

    Joined:
    Aug 12, 2009
    Posts:
    917
    Exactly depends on the operations you'll do on the data. From a performance stand point, reducing any sort of dynamic/growing buffer is good but sometimes you need it to execute your algorithm efficiently and that's why dynamic buffer exists.

    The best practice in DOD is to lok at your data and the operations that you'll do on it (transformations which need to happen for it) and then design your data structures based on that. I'm afraid this is the main point of DOD which is against such a question like is it best practice to always layout data like X?

    There are two things which unity people focus less on but performance by default here means, default is high performance and linear access but it doesn't mean you should not diverge from it when you have to.
     
    TMPxyz likes this.