> ## Documentation Index
> Fetch the complete documentation index at: https://ctrlrun.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# SchemaMismatch

> A store met a database it does not recognise, in either direction (SPEC-v0.6 §3.3).

`ctrlrun.SchemaMismatch` — class, defined at `src/ctrlrun/errors.py:205`

```python theme={null}
from ctrlrun import SchemaMismatch
```

```python theme={null}
class SchemaMismatch(CTRLRunError)
    def __init__(message: str, *, applied: tuple[str, ...] = (), known: tuple[str, ...] = (), running: str = '')
```

A store met a database it does not recognise, in either direction (SPEC-v0.6 §3.3).

Its own type rather than an `InvalidArgument`, and the bar it clears is that an operator's
process refusing to start needs a distinguishable exception: *"your database is from the
future"* and *"your lease is negative"* have entirely different remedies, and one bucket for
both would put a schema problem behind a wiring bug.

## Next

* [Python API index](/reference/api/index).
* [Get started](/get-started/quickstart) · [Why](/why).


## Related topics

- [Errors](/reference/errors.md)
- [Run on Postgres](/guides/run-on-postgres.md)
- [Migrations and schema versions](/production/migrations.md)
- [Fail closed](/concepts/fail-closed.md)
- [Python API](/reference/api/index.md)