2 000 000 documents in one xml file

I new to exist db. But i need to test performance on 2 000 000 generated objects.
I generated these objects and put it in one xml file.

every object looks like that

<objectn>
   <prop1>value</prop1>
   ...
   <prop10>value</prop10>
</objectn>

The query that gets all objects took 5-6 sec.
But the query holds on endlessly that receives objects by some properties or just to get the first object.
1GB memory granted to exist db on server.

Help please what i do wrong?