Realm Releases - Core 6 and multiple SDK updates

Realm Database 6.0 is now GA, with a significant increase in performance and Frozen Objects for multithreading integration. In addition to this, we’ve updated the following SDK’s -

and in conjunction with the above, Realm Studio 3.11.0 is now also released -

Please see the individual release notes to learn more and let us know, in the comments, what you think!

Many thanks

The MongoDB Realm Team

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First impression after upgrading on iOS was a crash on startup :frowning:
Keychain returned unexpected status code: -25299 · Issue #6494 · realm/realm-swift · GitHub. But I hope that get’s resolved soon :wink: After commenting out the Sync related code, it works and it was trivial to upgrade from the previous update.

Codewize, I had to change one line of code on iOS and nothing on Android. Except for the initial crash on iOS, both apps seem to run fine!

What performance improvements are we talking about? Do you have any measurements on these?

Can’t wait to test out the freezed objects and to see what you have in store for the public beta of Atlas sync. I am not live with Realm Cloud and have decided to hold off on doing this until the beta.

@Simon_Persson thank you for giving it a try and reporting an issue. When it comes to performance there are few gains:

  • The new architecture makes it faster to lookup objects based on a primary key
  • iOS benchmarks show faster insertions, twice as fast sorting, and ten times faster deletions
  • Code simplifications yielded a ten percent reduction in total lines of code and a smaller library
  • Realm files are now much smaller when storing big blobs or large transactions.

We also have a blog post from a bit earlier Realm Core Database 6.0: A New Architecture and Frozen Objects | MongoDB


I was Waiting eagerly for release of Realm Database 6.0 for dotnet. But didn’t get any updates on dotnet sdk. Does this mean dotnet is not in priority list of MongoDB Realm.

@Paramjit_Singh We got delayed on dotnet but are actively working on it. We hope to release it in the next week as well.


@Simon_Persson Running our highly artificial performance tests for Realm Cocoa on an iPad Air and comparing 4.x and 5.0 gives:

(x axis is percentage of runtime, so the first one took 1.7% as long with core 6 as with core 5, and the last one took 120% as long)

Overall we expect apps which were previously bottlenecked on our object deletion or sort performance to be a lot faster, and for most other use-cases to be a bit faster overall.


Looking forward to the .Net release. Still about a week away @Ian_Ward?

@Dr_Charles_Roddie Unfortunately not, we had some staff shortages and are delayed. I am hoping we can get it out in June

+1 on .Net SDK
and a migration guide from Realm Cloud will be great.


Hi, is Realm 6.0 100% compatible with Realm Cloud or might there be some issues with upgrading cocoa clients from Realm Swift v 4.x ?

Still hopeful for a .NET update on this!


Hi, is there documentation somewhere that explains what these new releases are and what compatibility they have with older versions, including Realm Cloud ?

I just tried opening a 4.6 database with the Realm Swift 5.1.0 release and it fails with an error “Key already used”.

I also noticed in the release notes for 5.0.2 (I think it was) that this is not compatible with Realm Cloud (legacy?!).

If that is the case then is there a plan for migration off realm cloud and if so what does that look like?


Hi Duncan,
I believe the best current docs are the release notes. If something there is unclear please let us know. But here is the gist:
As mentioned in this post we have updated all SDK’s (except .NET, which is lacking a little) with a new major version of the database. They all support Realm Cloud and we will continue to make important bug fixes in those, but don’t expect new features.

All SDK’s that supports the new MongoDB Realm Cloud is versioned “10.0.0-beta-*”. They contain both new data types and new features.

As for migration support from Realm Cloud to MongoDB Realm Cloud, we are working on that during this beta phase and will provide this as soon as we can.

Let us know if anything is unclear.


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Thanks for the prompt response. OK so in theory the 5.1.0 cocoa release should be compatible with an existing 4.x database and we should be able to upgrade to 5.1.0 and continue to sync with the existing Realm Cloud service.

Assuming that is the case is there someone I can contact regarding an error when trying to open a 4.x database with v5.1.0 - I am seeing a “Key already used” error from Realm. Happy to send you a copy of the database itself to test if required.

Yes - Cocoa v5 is fully compatible with existing Realm Cloud. So if you have any issues upgrading, please create a bug report in a github issue.


Thanks, I’ve done that.

Can we Dot Net developers expect any fixed date for the Realm Dot Net release.

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FYI it seems the RealmSwift 5.2.0 build fixes that previous issue - and you will be pleased to know it all seems work perfectly on Apple Silicon to - I just used Xcode to add the RealmSwift package. Great job guys - it’s blazingly fast too.