Module exonum::storage [−] [src]

A module that provides interfaces to work with the persisted blockchain data.

Database

A Database is a container for data persistence. Internally, a Database is a collection of named key-value stores (aka column families) with reading isolation and atomic writes. The database is assumed to be embedded, that is, the Exonum process has exclusive access to the DB during blockchain operation. You can interact with the Database from multiple threads by cloning its instance.

Exonum provides two database types: RocksDB and MemoryDB.

Snapshot and Fork

Snapshots and forks facilitate access to the database.

If you need to read the data, you can create a Snapshot using the snapshot method of the Database instance. Snapshots provide read isolation, so you are guaranteed to work with consistent values even if the data in the database changes between reads. Snapshot provides all the necessary methods for reading data from the database, so &Snapshot is used as a storage view for creating a read-only representation of the indices.

If you need to make changes to the database, you need to create a Fork using the fork method of the Database. Like Snapshot, Fork provides read isolation, but also allows to create a sequence of changes to the database that are specified as a Patch. A patch can be atomically merged into a database. Different threads may call merge concurrently.

`StorageKey` and `StorageValue` traits

If you need to use your own data types as keys or values in the storage, you need to implement the StorageKey or StorageValue traits respectively. These traits are already implemented for most standard types.

Indices

Indices are structures representing data collections stored in the database. This concept is similar to tables in relational databases. The interfaces of the indices are similar to ordinary collections (like arrays, maps and sets).

Each index occupies a certain set of keys in a single column family of the Database. On the other hand, multiple indices can be stored in the same column family, provided that their key spaces do not intersect. Isolation is commonly achieved with the help of prefixes; see with_prefix constructor in the built-in index types.

Merkelized indices can generate cryptographic proofs about inclusion of entries. Having such a proof, an external client may verify locally that the received data was authorized by the blockchain validators without having to replicate the entire blockchain contents.

Exonum provides the following index types:

Entry is a specific index that stores only one value. Useful for global values, such as configuration. Similar to a combination of Box and Option.
ListIndex is a list of items stored in the sequential order. Similar to Vec.
SparseListIndex is a list of items stored in the sequential order. Similar to ListIndex, but may contain indices without elements.
MapIndex is a map of keys and values. Similar to BTreeMap.
ProofListIndex is a Merkelized version of ListIndex that supports cryptographic proofs of existence and is implemented as a Merkle tree.
ProofMapIndex is a Merkelized version of MapIndex that supports cryptographic proofs of existence and is implemented as a binary Merkle Patricia tree.
KeySetIndex and ValueSetIndex is a set of items, similar to BTreeSet and HashSet.

To implement a new index type, you should create a wrapper around BaseIndex.

Re-exports

pub use self::base_index::BaseIndex;

pub use self::base_index::BaseIndexIter;

pub use self::map_index::MapIndex;

pub use self::list_index::ListIndex;

pub use self::sparse_list_index::SparseListIndex;

pub use self::key_set_index::KeySetIndex;

pub use self::value_set_index::ValueSetIndex;

pub use self::proof_list_index::ProofListIndex;

pub use self::proof_map_index::ProofMapIndex;

Modules

base_index	An implementation of base index with most common features.
key_set_index	An implementation of set for items that implement `StorageKey` trait.
list_index	An implementation of array list of items.
map_index	An implementation of key-value map.
proof_list_index	An implementation of a Merkelized version of an array list (Merkle tree).
proof_map_index	An implementation of a Merkelized version of a map (Merkle Patricia tree).
sparse_list_index	An implementation of array list of items with spaces.
value_set_index	An implementation of set for items that implement `StorageValue` trait.

Structs

Changes	Map containing changes with corresponding key.
ChangesIterator	Iterator over the `Changes` data.
Entry	An index that may only contain one element.
Error	The error type for I/O operations with storage.
Fork	A combination of a database snapshot and a sequence of changes on top of it.
MemoryDB	Database implementation that stores all the data in memory.
Patch	A set of serial changes that should be applied to a storage atomically.
PatchIterator	Iterator over the `Patch` data.
RocksDB	Database implementation on the top of `RocksDB` backend.
RocksDBOptions	Database-wide options around performance and behavior.

Enums

Change	An enum that represents a kind of change to some key in the storage.
ListProof	An enum that represents a proof of existence for a proof list elements.
MapProof	An enum that represents a proof of existence or non-existence for a proof map key.

Traits

Database	Low-level storage backend implementing a collection of named key-value stores (aka column families).
Iterator	A trait that defines streaming iterator over storage view entries.
Snapshot	A read-only snapshot of a storage backend.
StorageKey	A type that can be (de)serialized as a key in the blockchain storage.
StorageValue	A type that can be (de)serialized as a value in the blockchain storage.

Type Definitions

Iter	A generalized iterator over the storage views.
Result	A specialized `Result` type for I/O operations with storage.