Data Synchronization

Out-of-the-box Data Sync that goes hand-in-hand with the ObjectBox database. Easily share data across devices - seamless, bi-directional, selective data flows become easy with ObjectBox.

If you haven't tried out ObjectBox DB yet, get started here.

Welcome to the official documentation for ObjectBox Sync. We're thrilled to see your interest in our data synchronization solution and would like to ask you to sign up for early access here.

In a nutshell, here are the three steps to start with ObjectBox Sync:

  1. Set up your data model using one of the ObjectBox Sync Client language bindings (Java, Dart, Swift, C, ...) to get a data model JSON file.

  2. Start the server using the data model file.

  3. Point your sync client to the server URL to start syncing.

Please use the navigation on the left for more detailed information.

Sync Architecture

Sync Concepts

Typically you interact with your local ObjectBox database. It does not matter if the device is online or offline. You get and put objects using the regular ObjectBox APIs. If you are interested in details how that is done, please refer to the language binding of your choice: Java/Kotlin, Swift, Go, C++, Dart/Flutter (beta), Python (alpha).

The same APIs apply to synced objects, e.g. you use the same put call on a synced object as you would do for any (non-synced) object. Under the hood however, ObjectBox will synchronize those objects to their destination device, e.g. some server. Thus, those objects will become available outside of originating device.

Online, Offline, šŸ¤·

When you write applications with ObjectBox Sync, you usually do not bother if the device is online or offline. It does not matter. You work with the objects that you have at hand and let ObjectBox Sync "do its thing". But what is that exactly?

So, let's look a bit behind the scenes. Whenever you change data (on sync-enabled types), ObjectBox tracks these changes and stores them safely in an outgoing queue. In the background, ObjectBox Sync tries to connect to the data synchronization destination (Sync server). If the connection was successfully established, the outgoing queue is "processed". This means that enqueued data is send, and once the sync destination acknowledges the receipt, that piece of data can be safely removed from the queue.

When disconnected, Sync clients will periodically try to reconnect in the background. By default, this is done using increasing backoff intervals. While details may change, the backoffs should stay similar to this sequence [seconds]: 0.5, 1, 2, 4, 8, 15, 30, 30, 60. This resembles pretty much an exponential backoff, but also ensures not to delay a (re-)connection attempt for longer than one minute.

Delta synchronization

When you look at typical REST applications, a often used pattern is that clients request all data from the server. This happens regardless of any previous interaction; often because it's a simple approach and avoids caching (of course you are aware of the 3 hard problems in software: cache invalidation and off-by-one errors). Needless to say that this is not the most resource efficient setup as it involves redundant data processing and sub-optimal network traffic.

ObjectBox Sync does not follow the request-response paradigm. Instead, it pushes changes. This has several advantages like significantly reducing traffic while using less computing resources. Also, this enables "real-time" data updates out of the box.


ObjectBox Sync exchanges messages over the network. You do not interact with messages directly, but it is good to remember that; e.g you may see some message related charts in Sync statistics.

WebSockets is the standard protocol ObjectBox Sync uses to exchange messages. It borrows some advantages from HTTP for the handshake (e.g. usually plays nice with firewalls), while providing TCP-like properties. Thus and unlike HTTP, WebSockets enables fast two-way push communication. It also scales nicely: we have tested with hundreds of thousands concurrent clients connected to a single ObjectBox Sync server.

While WebSockets is a great match for ObjectBox Sync for most cases, we are not strictly bound to it. Internally, we have a network abstraction layer, which allows us to quickly adapt to special networking requirements like supporting LoRaWAN or other non-IP based protocols. Reach out to us if you are interested.

Robust data synchronization

Sync is tightly integrated with the ObjectBox database. In ObjectBox, when you put objects this always happens inside a database transaction. This is great to ensure that your data is always consistent. A cool thing about ObjectBox Sync is that it uses the same database transaction for meta data used by synchronization. Thus, that though level of consistency, which databases offer extends to Sync. Sync meta data can not diverge from the actual data.

OK, this may sound a bit abstract, so let's look at an example. Let's say device A is constantly computing data based on a never ending stream of sensor data. Also that computed data is synced to a edge gateway B. Now at any point in time, device A suddenly looses power. Don't worry, your data is safe and consistent. Transactions ensure that the state on device A is consistent with what will be synchronized to gateway B. ObjectBox takes care of all that; no matter if A and B were connected to each other or whatever the synchronization state was at the point when the power went out. Once device A boots up again, ObjectBox will synchronize data to gateway B from the point it was interrupted.

Future Sync

Our vision of providing data where it's needed when it's needed goes way beyond what we already have implemented. Contact us and be part of that exciting journey. We will listen to where you want to go; let us provide the infrastructure so you can focus on your core product.

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