Ignite vault module

This module provides Vault API implementation.

Vault is the local persistent key-value storage where node maintains its local state. The data stored in the vault is semantically divided in the following categories:

• User-level local configuration properties (such as memory limits, network timeouts, etc). User-level configuration properties can be written both at runtime (not all properties will be applied at runtime, however, - some of them will require a full node restart) and when a node is shut down (in order to be able to change properties that prevent node startup for some reason)
• System-level private properties (such as computed local statistics, node-local common paths, etc). System-level private properties are computed locally based on the information available at node locally (not based on metastorage watched values)
• System-level distributed metastorage projected properties (such as paths to partition files, etc). System-level projected properties are associated with one or more metastorage properties and are computed based on the local node state and the metastorage properties values. System-level projected properties values are semantically bound to a particular revision of the dependee properties and must be recalculated when dependees are changed (see reliable watch processing).

The main components of the module are the following:

• VaultEntry is the vault unit as entry with comparable key represented as a ByteArray and value represented as an array of bytes.
• VaultService defines interface for accessing to a vault service. There are standard methods for working with keys and values like get VaultEntry by key, put value with key to vault, remove value with a key from vault, putAll method that inserts or updates entries with given keys and given values. Also there is a range method that returns a view of the portion of vault whose keys range from fromKey, inclusive, to toKey, exclusive.
• VaultManager is responsible for handling VaultService lifecycle and providing interface for managing local keys.

There are two implementations of VaultService: InMemoryVaultService and PersistentVaultService. The first one is the in-memory implementation of VaultService and mostly used for testing purposes.

The second one is VaultService implementation based on RocksDB. RocksDB is a storage engine with key/value interface, where keys and values are arbitrary byte streams. For more info about RocksDB see corresponding wiki.