The short answer as to what people normally do is that they use a
relational database for something like this.
I'm curious as to how you would have so many asset / user permissions that
you couldn't use a standard relational database to model them. Is this some
sort of multi-tenant system where you're providing some generalized asset
check-out mechanism to many, many customers? Even so, I'm not sure the
eventually consistent model wouldn't open you up to check-out collisions,
as you mention yourself.
Am I missing something about your example?
On Apr 20, 2010 9:47am, tsuraan <tsur...@gmail.com> wrote:
> Suppose I have a CF that holds some sort of assets that some users of
> my program have access to, and that some do not. In SQL-ish terms it
> would look something like this:
>
> TABLE Assets (
> asset_id serial primary key,
> ...
> );
>
> TABLE Users (
> user_id serial primary key,
> user_name text
> );
>
> TABLE Permissions (
> asset_id integer references(Assets),
> user_id integer references(Users)
> )
>
> Now, I can generate UUIDs for my asset keys without any trouble, so
> the serial that I have in my pseudo-SQL Assets table isn'ta problem.
> My problem is that I can't see a good way to model the relationship
> between user ids and assets. I see one way to do this, which has
> problems, and I think I sort of see a second way.
>
> The obvious way to do it is have the Assets CF have a SuperColumn that
> somehow enumerates the users allowed to see it, so when retrieving a
> specific Asset I can retrieve the users list and ensure that the user
> doing the request is allowed to see it. This has quite a few
> problems. The foremost is that Cassandra doesn't appear to have much
> for conflict resolution (at least I can't find any docs on it), so if
> two processes try to add permissions to the same Asset, it looks like
> one process will win and I have no idea what happens to the loser.
> Another problem is that Cassandra's SuperColumns don't appear to be
> ideal for storing lists of things; they store maps, which isn'ta
> terrible problem, but it feels like a bit of a mismatch in my design.
> A SuperColumn mapping from user_ids to an empty byte array seems like
> it should work pretty efficiently for checking whether a user has
> permissions on an Asset, but it also seems pretty evil.
>
> The other idea that I have is a seperate CF for AssetPermissions that
> somehow stores pairs of asset_ids and user_names. I don't know what
> I'd use for a key in that situation, so I haven't really gotten too
> far in seeing what else is broken with that idea. I think it would
> get around the race condition, but I don't know how to do it, and I'm
> not sure how efficient it could be.
>
> What do people normally use in this situation? I assume it's a pretty
> common problem, but I haven't see it in the various data modelling
> examples on the Wiki.
I'm wondering, is my question too vague, too specific, off topic for
this list, or answered in the docs somewhere that I missed?
