btcd数据库设计 ​

// db represents a collection of namespaces which are persisted and implements
// the database.DB interface.  All database access is performed through
// transactions which are obtained through the specific Namespace.
type db struct {
	writeLock sync.Mutex   // Limit to one write transaction at a time.
	closeLock sync.RWMutex // Make database close block while txns active.
	closed    bool         // Is the database closed?
	store     *blockStore  // Handles read/writing blocks to flat files.
	cache     *dbCache     // Cache layer which wraps underlying leveldb DB.
}
// transaction represents a database transaction.  It can either be read-only or
// read-write and implements the database.Bucket interface.  The transaction
// provides a root bucket against which all read and writes occur.
type transaction struct {
	managed        bool             // Is the transaction managed?
	closed         bool             // Is the transaction closed?
	writable       bool             // Is the transaction writable?
	db             *db              // DB instance the tx was created from.
	snapshot       *dbCacheSnapshot // Underlying snapshot for txns.
	metaBucket     *bucket          // The root metadata bucket.
	blockIdxBucket *bucket          // The block index bucket.

	// Blocks that need to be stored on commit.  The pendingBlocks map is
	// kept to allow quick lookups of pending data by block hash.
	pendingBlocks    map[chainhash.Hash]int
	pendingBlockData []pendingBlock

	// Keys that need to be stored or deleted on commit.
	pendingKeys   *treap.Mutable
	pendingRemove *treap.Mutable

	// Active iterators that need to be notified when the pending keys have
	// been updated so the cursors can properly handle updates to the
	// transaction state.
	activeIterLock sync.RWMutex
	activeIters    []*treap.Iterator
}
// bucket is an internal type used to represent a collection of key/value pairs
// and implements the database.Bucket interface.
type bucket struct {
	tx *transaction
	id [4]byte
}
// cursor is an internal type used to represent a cursor over key/value pairs
// and nested buckets of a bucket and implements the database.Cursor interface.
type cursor struct {
	bucket      *bucket
	dbIter      iterator.Iterator
	pendingIter iterator.Iterator
	currentIter iterator.Iterator
}