Custom Drivers

Database drivers implement queen.Driver:

type Driver interface {
    Init(ctx context.Context) error
    GetApplied(ctx context.Context) ([]Applied, error)
    Record(ctx context.Context, m *Migration, meta *MigrationMetadata) error
    Remove(ctx context.Context, version string) error
    Lock(ctx context.Context, timeout time.Duration) error
    Unlock(ctx context.Context) error
    Exec(ctx context.Context, isolationLevel sql.IsolationLevel, fn func(*sql.Tx) error) error
    Close() error
}

Init prepares history storage. GetApplied, Record, and Remove read and update it. Lock and Unlock coordinate concurrent migrators. Exec runs migration code using the driver's transaction semantics and requested isolation level where supported. Close releases resources.

Implement TransactionalRecorder if the database can write a history row inside the same transaction as the migration body. Its RecordTx and RemoveTx methods let SQL and history commit or roll back together. Optional MigrationExecutor supports per-migration SQL timeouts; NonTransactionalExecutor supports single-command SQL outside a transaction with recovery markers. SQLDBProvider exposes the underlying *sql.DB for diagnostics.

Use the PostgreSQL driver as the reference for connection-pinned locking and transactional recording. Describe any weaker guarantees in your driver's documentation so deploy jobs can account for them.