---
title: Limits and gaps
editUrl: https://github.com/Cratis/Chronicle.Elixir/edit/main/Documentation/limits-and-gaps.md
description: Kernel limits to size your data against, the consistency guarantees of appends and projections, and what the Elixir client does not do yet.
---


## Kernel limits

| Limit | Value | What happens |
| --- | --- | --- |
| Message size | 4 MiB per gRPC message | The client refuses larger payloads with `{:error, {:payload_too_large, size, limit}}`; a reducer whose read model exceeds it reports the reduction as failed. Configure with `config :cratis_chronicle, max_payload_bytes: ...`. |
| Read model document | 4 MiB | Roughly 18,000 entries at 220-250 bytes each. A child collection that can grow without bound belongs in its own read model per child, not one document. |
| Observer subscriber deadline | `observers.subscriberTimeout`, 5 seconds by default | Applies to a reactor or reducer handling one batch. Keep handlers fast, and size partitions so a backlog delivered in one call finishes within it. |
| Filtered read model queries | `:max_scan`, 10,000 instances | See [Filtering and sorting](/chronicle/clients/elixir/read-models/#filtering-and-sorting): the filter is applied by the client. |

## Consistency

- `Chronicle.append/3` returning `:ok` means the event is stored. Projections, reducers and reactors process it **afterwards and asynchronously**.
- A read model read right after an append, including `append_many/3`, may not reflect it yet. When you need your own write, use `Chronicle.EventSequences.EventLog.append_and_wait_for_completion/3` or `AppendResult.wait_for_completion/2`, which return once the affected observers have processed the event (or failed).
- `await_registration/2` returns once the client's artifacts are registered. Observers subscribe right after; wait for the first events you depend on with the calls above rather than sleeping.
- `get/3` returns `{:ok, nil}` both for a key that does not exist and for one that is not projected yet.

## Security

`skipTlsValidation` defaults to `true` so that a development kernel works without setup. A connection to a remote host that skips validation logs a warning at startup. Production connection strings must say `skipTlsValidation=false`; see [Connection strings](/chronicle/clients/elixir/connections/connection-strings/#tls).

## Not supported yet

- Patterns queries (`Chronicle.Patterns`) are tracked in the repository's issues.
- Distributed tracing and metrics beyond the observer lag event: OpenTelemetry instrumentation is tracked in the issues.
- Captures (declarative capture of external input into events) have no Elixir DSL yet.
- Decision reads and unit-of-work-guarded reads (the dynamic consistency boundary) are not available through the client; use a history fold and concurrency scopes (`expecting_no_matching_event/1`).
- An in-memory Chronicle for tests: specs run against a kernel.
- The filter of `query/2` is evaluated by the client, not the kernel.

See the repository's open issues for the current list.