How-To get consecutive id with RavenDb default id generator
Solution 1:
This is by design - new HiLo keys are generated whenever you create a DocumentStore instance, so the gaps you are seeing are the unused ids from the other session.
Why do you care for consecutive ids?
This may be a good read on the subject, too: http://groups.google.com/group/ravendb/browse_thread/thread/3dbcacbc8b366ff8/
Solution 2:
From the RavenDb documents, you're after the Identity strategy.
RavenDB also supports the notion of Identity, for example if you need IDs to be consecutive. By creating a string Id property in your entity, and setting it to a value ending with a slash (/), you can tell RavenDB to use that as a key perfix for your entity. That prefix followed by the next available integer ID for it will be your entity's ID after you call SaveChanges().
eg.
var foo = new Foo();
foo.Id = "foo/"; // <-- this will use the Identity strategy, not HiLo.
session.Store(foo);
session.SaveChanges();