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Handle Sync Errors and Timeouts - .NET SDK

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  • Set the Client Log Level
  • Customize the Logging Function
  • Handle Timeouts

Device Sync represents errors via SessionExceptions. In addition to the standard exception properties, you have access to an ErrorCode that contains information about the type of the error and allows you to have strongly typed handling logic.

config.OnSessionError = (session, sessionException) =>
switch (sessionException.ErrorCode)
// See
// for a list of all error codes
case ErrorCode.BadQuery:


Additional Exception Information

For security reasons, App Services may send only a minimal amount of information about an exception, but the server-side logs will contain more details. In these cases, the HelpLink property on the exception contains a link to the associated log entry.


For a list of common Device Sync errors and how to handle them, refer to Sync Errors in the App Services Device Sync documentation.

To control which messages are logged by the client logger, use LogLevel:

Logger.LogLevel = LogLevel.Debug;


To diagnose and troubleshoot errors while developing your application, set the log level to debug or trace. For production deployments, decrease the log level for improved performance.

To set a custom logger function, set Logger.Default to a custom Logger function.

using Realms.Logging;
Logger.LogLevel = LogLevel.All;
// customize the logging function:
Logger.Default = Logger.Function(message =>
// Do something with the message

During Sync sessions, events may timeout without throwing an exception. You can set the CancelAsyncOperationsOnNonFatalErrors to true so that these events throw an exception that you can then handle. The following code shows an example of setting the CancelAsyncOperationsOnNonFatalErrors property, and 3 events that will throw an exception if they timeout:

var config = new FlexibleSyncConfiguration(app.CurrentUser!)
CancelAsyncOperationsOnNonFatalErrors = true,
// These operations will throw an exception
// on timeout or other transient sync session errors.
var realm = await Realm.GetInstanceAsync(config);
var session = realm.SyncSession;
await session.WaitForUploadAsync();
await session.WaitForDownloadAsync();
← Manage Flexible Sync Subscriptions