db4o Indexing problem - Not Working? Poor performance?

Question

Hi there,

I'm attempting to use db4o as the back-end for my new website.

I've set things up, as I thought sensible, and have inserted about 5k records (of only one object type, with about 7 primitive fields).

As per some blog posts I've read, I've setup the properties as non-automatic properties, and tried to set indexes on the private members exposed by the public properties.

Query performance is really bad, with what should be a simple indexed lookup taking upto 3/4 seconds.

My implementation is a follows: My 'Server' is a static singleton, only opened once per application instance.

Db4oFactory.Configure().ObjectClass(typeof(MyObject)).ObjectField("_Id").Indexed(true);
server = Db4oClientServer.OpenServer("DatabseName", 0);

then, to query:

using (var ooDB = server.OpenClient())
{
    var movieFound = (from MyObject m in ooDB
                    where m.Id == IdToFind
                    select m).FirstOrDefault();
}

With my object as:

public class MyObject
{
    protected string _Id;
    public string Id 
    { 
        get { return _Id; } 
        set { _Id = value; } 
    }
}

The Object's Id is a string.

What am I doing wrong!

Cheers, Dave

Answer 1

I haven't used db4o for a while, but what strikes me here is that you query the property and create an index on the backing field. Unless db4o manages to understand the relationship (it might, but I doubt it for now) it's going to revive every stored instance to access the property and evaluate your query..

Can you link to the posts that asked for this kind of setup for the indices?

Answer 2

This is a case of an unlucky combination of the old API (version 7.4, still here for compatibility) and new API (version 7.12). The configuration isn't used, so no index is created.

The method call 'Db4oFactory.Configure()' belongs to the older API. It is only used when you create an ObjectContainer with the old API: 'Db4oFactory.OpenServer()'. This global configuration has some potential problem. So I would avoid it.

Now I recommend to use the new API. There you have to pass the configuration explicit. Also the configuration interface is more clean. Especially is the client/server configuration separated. Use 'Db4oClientServer.NewServerConfiguration()' to create a new configuration. And then pass it to 'Db4oClientServer.OpenServer'. So in your case this would be:

        IServerConfiguration cfg = Db4oClientServer.NewServerConfiguration();
        cfg.Common.ObjectClass(typeof(MyObject)).ObjectField("_Id").Indexed(true);

        IObjectServer server = Db4oClientServer.OpenServer(cfg, "DatabseName.db4o", 0);