Consider using Raven compare/exchange to ensure uniqueness

[JudahGabriel]

We're currently relying on unique doc IDs to ensure unique emails/usersnames.

That's fine for a single database, but may not work in a cluster. Thus, we should use Raven compare/exchange to ensure uniqueness.

If we do that, we probably will no longer need IdentityUsersByUserName.

[marcuslindblom]

Are you still considering to change this?

[JudahGabriel]

Yes. I'll see if I can make this happen this week.

[JudahGabriel]

Implemented. RavenDB.Identity v6, which is now on NuGet, uses compare/exchange to ensure email address uniqueness across clusters.

This has two side-effects, one good and one bad:

• The good: We no longer store 2 entities per user; IdentityUserByUserName is obsolete. You can safely delete this collection.
• The bad: If you were using a previous version of RavenDB.Identity and you're upgrading to v6 or later, you must call UserStore<AppUser>.MigrateToV6(docStore). Note that the method can take several minutes to run if you have thousands of users. Failure to do so will result in your users not being able to login. The MigrateToV6 method creates a compare/exchange value for each email address.