Select all that are true of database checkpoints. $($Check all that are true.$)$

a$.$

Database checkpoints are operations in which the DBMS writes all updated $("$dirty$")$ block buffers in the RAM block buffer cache to durable storage. This enables recovery of the database state at the time of the checkpoint from disk or other storage.

b$.$

Checkpoints must be scheduled by an administrator to assure database recoverability.

c$.$

A checkpoint operation is recorded in the transaction log$.$

d$.$

Checkpoints play an important role in transaction recovery.