Crate linera_viewsCopy item path

This module is used in the Linera protocol to map complex data structures onto a key-value store. The central notion is a views::View which can be loaded from storage, modified in memory, and then committed (i.e. the changes are atomically persisted in storage).

The package provides essentially two functionalities:

• An abstraction to access databases.
• Several containers named views for storing data modeled on classical ones.

See DESIGN.md for more details.

§The supported databases.

The databases supported are of the NoSQL variety and they are key-value stores.

We provide support for the following databases:

• MemoryDatabase is using the memory
• RocksDbDatabase is a disk-based key-value store
• DynamoDbDatabase is the AWS-based DynamoDB service.
• ScyllaDbDatabase is a cloud-based Cassandra-compatible database.
• StorageServiceDatabase is a gRPC-based storage that uses either memory or RocksDB. It is available in linera-storage-service.

The corresponding trait in the code is the crate::store::KeyValueDatabase. as well as crate::store::KeyValueStore.

The latter trait decomposes into a store::ReadableKeyValueStore and a store::WritableKeyValueStore.

A context is the combination of a client and a base key (of type Vec<u8>).

§Views.

A view is a container whose data lies in one of the above-mentioned databases.

When the container is modified the modification lies first in the view before being committed to the database. In technical terms, a view implements the trait View.

The specific functionalities of the trait View are the following:

• context for obtaining a reference to the storage context of the view.
• load for loading the view from a specific context.
• rollback for canceling all modifications that were not committed thus far.
• clear for clearing the view, in other words for reverting it to its default state.
• flush for persisting the changes to storage.

The following views implement the View trait:

• RegisterView implements the storing of a single data.
• LogView implements a log, which is a list of entries that can be expanded.
• QueueView implements a queue, which is a list of entries that can be expanded and reduced.
• MapView implements a map with keys and values.
• SetView implements a set with keys.
• CollectionView implements a map whose values are views themselves.
• ReentrantCollectionView implements a map for which different keys can be accessed independently.
• ViewContainer<C> implements a KeyValueStore and is used internally.

The LogView can be seen as an analog of VecDeque while MapView is an analog of BTreeMap.