BoltDB 事务流程

// txid represents the internal transaction identifier.
type txid uint64

// Tx represents a read-only or read/write transaction on the database.
// Read-only transactions can be used for retrieving values for keys and creating cursors.
// Read/write transactions can create and remove buckets and create and remove keys.
type Tx struct {
    writable       bool
    managed        bool
    db             *DB
    meta           *meta
    root           Bucket
    pages          map[pgid]*page
    stats          TxStats
    commitHandlers []func()

    // WriteFlag specifies the flag for write-related methods like WriteTo().
    // Tx opens the database file with the specified flag to copy the data.
    WriteFlag int
}