I am looking for a way of doing an efficient caching system for an ES.

all update are made in memory (but only requiered/active parts of the DB are loaded) and periodically the cache is saved to the DB, the problem I found is that how to efficiently cache components of my entities without explode memory and keep an extremly fast acces to component based on their entity ID ?
for now I got something like the following :

use native array for memory storing
  => String componentLabel[];
  => Point3D componentLocation[];

and use an hastable to get entity index in natives arrays :
 => Hashtable<Integer,Integer> entityIDtoNativeArrayIndex;

I only use one hastable that give me the index of the entity for each possible components, I was wondering if anybody have a better idea ?  one problem I could face later will be that :
- memory used for an entity with only one component will be always equals to the size of all componenets.
- a new componenent will make a big memory grow (for all active entity it will exist an entry).

any (simple..) idea to compact this structure (wich is basically a 2D array with size equals to activeEntity*nbComponent) in an efficient manner  ?


EDIT:

what I need is to be able to get a list of all entity having a component of type "XXX" while still being able to faslty access some other component of those entities.

something that may look like :

where havingAppearance & havingPhysics may overlap

first :

an entity classe :


and an entity native array :


some components natives array :


with each component having a properties entityIndex on a supperclass



so I can get all entity with a given component by just reading the component native array, and access any other component faslty


sounds pretty efficient, the only thing more I would requiere is an Entity class that dont always use an int per possible components...

EDIT: typos

so finally end with something that I am satisfy with, will not explain details as it is internally very similar to the previous post :

one native array for all components :


an entity array and a fast index acces Hastable


the new point is that I added an EntityManager that is responsible of adding new entity and/or components, every component added to an entity is added by the entitymanager every new entity is added by the entity manager, this enable good integrity and nivce looking code and good eficiency,
code looks like :


than later



and still able to threat componnents as blocks for systems or DB saving with cross access to other components of the current entity



the EntityManager is responsible to maintain coherence between component & entity, all storage (component/entity) is made in native arrays, the Entity class is only usefull to enable cross component access and fast entity loading (in DB it give for an entity all components it use => direct DB modifcation are then inded not alowed to keep DB integrity).

I understand what you mean and have similar feeling than you, it would have been a lot easier (faster) to make something more specific but I really wanted to find something more generic to let 'more open ways for the futur'

this is for an online game : MMO and we can say in a certain manner MMORPG (even if there wont be any magic, potion, dwarf or such...)


EDIT: the slower part is to get an entity by its ID (use of the hashtable) but it should not be used a lot, all other acces are direct acces : all component keep a direct link to its entity and all entity keep a direct link to each of its components

thanks as I said above it is not a bottlneck but if you can point me a link to this one and if it make a significant improvment it will be nice anyway