Storage

Overview

The ZChains currently utilizes LevelDB for data storage, as well as an in-memory data store.

Throughout the ZChains, when modules need to interact with the underlying data store, they don't need to know which DB engine or service they're speaking to.

The DB layer is abstracted away between a module called Storage, which exports interfaces that modules query.

Each DB layer, for now only LevelDB, implements these methods separately, making sure they fit in with their implementation.

// Storage is a generic blockchain storage
type Storage interface {
	ReadCanonicalHash(n uint64) (types.Hash, bool)
	WriteCanonicalHash(n uint64, hash types.Hash) error

	ReadHeadHash() (types.Hash, bool)
	ReadHeadNumber() (uint64, bool)
	WriteHeadHash(h types.Hash) error
	WriteHeadNumber(uint64) error

	WriteForks(forks []types.Hash) error
	ReadForks() ([]types.Hash, error)

	WriteDiff(hash types.Hash, diff *big.Int) error
	ReadDiff(hash types.Hash) (*big.Int, bool)

	WriteHeader(h *types.Header) error
	ReadHeader(hash types.Hash) (*types.Header, error)

	WriteCanonicalHeader(h *types.Header, diff *big.Int) error

	WriteBody(hash types.Hash, body *types.Body) error
	ReadBody(hash types.Hash) (*types.Body, error)

	WriteSnapshot(hash types.Hash, blob []byte) error
	ReadSnapshot(hash types.Hash) ([]byte, bool)

	WriteReceipts(hash types.Hash, receipts []*types.Receipt) error
	ReadReceipts(hash types.Hash) ([]*types.Receipt, error)

	WriteTxLookup(hash types.Hash, blockHash types.Hash) error
	ReadTxLookup(hash types.Hash) (types.Hash, bool)

	Close() error
}

LevelDB

Prefixes

In order to make querying the LevelDB storage deterministic, and to avoid key storage clashing, the ZChains leverages prefixes and sub-prefixes when storing data

// Prefixes for the key-value store
var (
	// DIFFICULTY is the difficulty prefix
	DIFFICULTY = []byte("d")

	// HEADER is the header prefix
	HEADER = []byte("h")

	// HEAD is the chain head prefix
	HEAD = []byte("o")

	// FORK is the entry to store forks
	FORK = []byte("f")

	// CANONICAL is the prefix for the canonical chain numbers
	CANONICAL = []byte("c")

	// BODY is the prefix for bodies
	BODY = []byte("b")

	// RECEIPTS is the prefix for receipts
	RECEIPTS = []byte("r")

	// SNAPSHOTS is the prefix for snapshots
	SNAPSHOTS = []byte("s")

	// TX_LOOKUP_PREFIX is the prefix for transaction lookups
	TX_LOOKUP_PREFIX = []byte("l")
)

// Sub-prefixes
var (
	HASH   = []byte("hash")
	NUMBER = []byte("number")
	EMPTY  = []byte("empty")
)

Future Plans

The plans for the near future include adding some of the most popular DB solutions, such as:

• PostgreSQL

• MySQL

📜 Resources

• LevelDB