# dynamo-es
> A DynamoDB implementation of the `PersistedEventRepository` trait in cqrs-es.
### DynamoDb caveats
AWS' DynamoDb is fast, flexible and highly available, but it does
[set some limitations](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ServiceQuotas.html)
that must be considered in the design of your application.
#### Maximum limit of 25 operations in any transaction
Events are inserted in a single transaction, which limits the number of events that can be handled from a single command
using this repository. To operate correctly a command must not produce more than
- 25 events if using [an event store without snapshots](https://docs.rs/cqrs-es/latest/cqrs_es/persist/struct.PersistedEventStore.html#method.new_event_store)
- 24 events if using [snapshots](https://docs.rs/cqrs-es/latest/cqrs_es/persist/struct.PersistedEventStore.html#method.new_snapshot_store)
or [an aggregate store](https://docs.rs/cqrs-es/latest/cqrs_es/persist/struct.PersistedEventStore.html#method.new_aggregate_store)
#### Item size limit of 400 KB
A single event should never reach this size, but a large serialized aggregate might.
If this is the case for your aggregate beware of using [snapshots](https://docs.rs/cqrs-es/latest/cqrs_es/persist/struct.PersistedEventStore.html#method.new_snapshot_store)
or [an aggregate store](https://docs.rs/cqrs-es/latest/cqrs_es/persist/struct.PersistedEventStore.html#method.new_aggregate_store).
#### Maximum request size of 1 MB
This could have the same ramifications as the above for [snapshots](https://docs.rs/cqrs-es/latest/cqrs_es/persist/struct.PersistedEventStore.html#method.new_snapshot_store)
or [an aggregate store](https://docs.rs/cqrs-es/latest/cqrs_es/persist/struct.PersistedEventStore.html#method.new_aggregate_store).
Additionally, an aggregate instance with a large number of events may reach this threshold.
To prevent an error while loading or replaying events,
[set the streaming channel size](https://docs.rs/dynamo-es/latest/dynamo_es/struct.DynamoEventRepository.html#method.with_streaming_channel_size)
to a number that ensures you won't exceed this threshold.
### Testing
Requires access to DynamoDb with existing tables. This can be created locally using the included
`docker-compose.yml` file with CLI configuration of test tables included in the `Makefile`.
To prepare a local test environment (requires a local installation of
[Docker](https://www.docker.com/products/docker-desktop) and
[AWS CLI](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-welcome.html)):
- `docker-compose up -d`
- `make configure`
Note that this crate used the [AWS DynamoDb Rust SDK](https://aws.amazon.com/sdk-for-rust/), which is currently in
Developer Preview. This means that any bugs will be addressed but the underlying interfaces may still be changed
resulting in significant changes within this crate. See the
[AWS SDK public roadmap for more information](https://github.com/awslabs/aws-sdk-rust/projects/1).
It is recommended that tables are configured to allow only transactions.
See:
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/transaction-apis-iam.html
---
Things that could be helpful:
- [User guide](https://doc.rust-cqrs.org) along with an introduction to CQRS and event sourcing.
- [Demo application](https://github.com/serverlesstechnology/cqrs-demo) using the warp http server.
- [Change log](https://github.com/serverlesstechnology/cqrs/blob/master/change_log.md)
[](https://crates.io/crates/dynamo-es)
[](https://docs.rs/dynamo-es)
