We spoke about error handling last week, so will continue on the same trend this week as the “Bad Changeset” error has been frequently asked by a lot of you and it sometimes gets tricky to troubleshoot why this is happening or how this can be fixed.
This week, let’s learn some tips and tricks around the error, and some proactive steps you can take to prevent this error from happening.
*Depending on the use-case and implementation of code in your application, sometimes the error can still happen, but hopefully with the information below you will have more understanding of the Sync process.
What is a changeset?
A changeset is a set of instructions that specify a change(s) to a Realm object(s) after a write operation. This along with some metadata is exchanged between a client(mobile) and the Sync Server to keep your data in Sync. Check Realm Sync Protocol section to learn more.
What is a Bad Changeset?
A changeset is termed as Bad when instructions from the client do not match the server (UPLOAD) that leads to Server-side error or when the instructions from the Server do not match the client (DOWNLOAD), that leads to a Bad Changeset on the client and hence the data cannot be merged and Syncing of the data stops for the client.
Different Error Variations
(but not limited to)
- “upload is invalid: upload progress (clientVersion=698, lastIntegratedServerVersion=356) is mutually inconsistent with threshold (clientVersion=697, lastIntegratedServerVersion=357) (ProtocolErrorCode=209)”
- ERROR: Connection[2]: Session[2]: Failed to parse, or apply received changeset: EraseObject: Table ‘class_Organisation’ does not exist (version: 47, last_integrated_remote_version: 1, origin_file_ident: 62, timestamp: 213527383911)
- Failed to open realm: { message: ‘Bad changeset (DOWNLOAD)’, errorCode: 1 }
- {“name”:“Error”,“message”:“Bad changeset (DOWNLOAD)”,“isFatal”:true,“category”:“realm::sync::ClientError”,“code”:112,“userInfo”:{}}
What Causes a Bad Changeset and How to Resolve it?
The reasons can vary every time. The Bad Changeset occurs when you make changes that are not permitted or do not update SDK to a newer version that has fixes.
-
Schema Inconsistencies
- Mismatch of Client Schema and Server Schema – For instance, a difference in Optional vs Required Fields
- Destructive Schema Changes from client-side
- Schema changes made on the client-side (but not the server-side) with development mode off
-
Partition Issues
- Inserting data with an incorrect partition value
- Read/Write operations that are not permitted by Realm Sync permissions
-
Continuing to access a Synced Collection after it has been dropped
-
Using the old Realm SDK version that should have been updated
The recommended way to resolve this is to prevent these inconsistencies in your code. Some helpful documentation links are
Depending on the use case you may be required to Terminate and Re-Enable Sync to fix the state of the application. Or if this is only happening for a specific device, having that client perform a client reset may solve
If you cannot limit the cause to any of this in the list, then you may be experiencing server-side inconsistency. The recommendation is to open a post on the forum with complete details of the error log.
I hope the provided information is helpful.
Please feel free to share any information that came useful to you or any different methods you used to resolve the Bad Changeset situation.
Happy Realming! 
But better safe than sorry.