Return true if there is an active transaction.
Begin a transaction in the current fiber.
A transaction is attached to caller fiber, therefore one fiber can have only one active transaction.
Returns: 0 on success Returns: -1 on error. Perhaps a transaction has already been started
Commit the current transaction.
Returns: 0 on success Returns: -1 on error. Perhaps a disk write failure
Rollback the current transaction.
Allocate memory on txn memory pool.
The memory is automatically deallocated when the transaction is committed or rolled back.
Returns: NULL on out of memory