Limits and gaps

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: 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.

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.