Storage

Overview

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

Throughout the xBuildApp , 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.

Copy

// 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 xBuildApp leverages prefixes and sub-prefixes when storing data

Copy

// 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