# Schema Mismatch

## Issue

A cqlsh operation failed with `schema version mismatch detected` error message.

For example

```shell
OperationTimedOut: errors={'10.1.1.54': 'Request timed out while waiting for schema agreement. See Session.execute[_async](timeout) and Cluster.max_schema_agreement_wait.'}, last_host=10.1.1.54
Warning: schema version mismatch detected; check the schema versions of your nodes in system.local and system.peers.
```

## Problem

One or more ScyllaDB nodes have a schema mismatch.

## How to Verify

Run [nodetool describecluster](https://docs.scylladb.com/manual/master/operating-scylla/nodetool-commands/describecluster.md)

In the following example, one node, **172.17.0.3** has a different schema than the other two nodes. As a temporary state, this is fine, but if this state persists, it will fail CQL operations.

```cql
Cluster Information:
        Name: Test Cluster
        Snitch: org.apache.cassandra.locator.SimpleSnitch
        DynamicEndPointSnitch: disabled
        Partitioner: org.apache.cassandra.dht.Murmur3Partitioner
        Schema versions:
                f04247d2-e2a6-3785-9fb8-8a57c7bdb25c: [172.17.0.1, 172.17.0.2]
                b1c9af1d-4f90-39fb-a869-95eeb3da96af: [172.17.0.3]
```

## Solution

1. Wait for five minutes and run `nodetool describecluster` to verify that the schema is synced.
2. If there is still a mismatch error message execute a [rolling restart](https://docs.scylladb.com/manual/master/operating-scylla/procedures/config-change/rolling-restart.md).
3. Verify schema is synced

For example:

```cql
Cluster Information:
        Name: Test Cluster
        Snitch: org.apache.cassandra.locator.SimpleSnitch
        DynamicEndPointSnitch: disabled
        Partitioner: org.apache.cassandra.dht.Murmur3Partitioner
        Schema versions:
                1fd57629-6bae-3f23-97d1-ffa4208cc372: [172.17.0.1, 172.17.0.2, 172.17.0.3]
```