Which three events signal a database writer (DWR) to write buffers to disk?

Question

Options

• AThe database advances a checkpoint.
• BA client process commits a transaction.
• CThe redo log buffer becomes full.
• DA server process cannot find non-dirty blocks after scanning a threshold number of buffers.
• EA tablespace is changed to read-only status.
• FThe database is shut down in immediate mode.

• A
  82% (31)
• B
  5% (2)
• C
  3% (1)
• E
  11% (4)

Explanation

https://docs.oracle.com/database/121/CNCPT/process.htm#BABHDJGD The DBW process writes dirty buffers to disk under the following conditions: - When a server process cannot find a clean reusable buffer after scanning a threshold number of buffers, it signals DBW to write. DBW writes dirty buffers to disk asynchronously if possible while performing other processing. - DBW periodically writes buffers to advance the checkpoint, which is the position in the redo thread from which instance recovery begins (see "Overview of Checkpoints"). The log position of the checkpoint is determined by the oldest dirty buffer in the buffer cache. When Oracle Database Initiates Checkpoints The checkpoint process (CKPT) is responsible for writing checkpoints to the data file headers and control file. Checkpoints occur in a variety of situations. For example, Oracle Database uses the following types of checkpoints: - Thread checkpoints The database writes to disk all buffers modified by redo in a specific thread before a certain target. The set of thread checkpoints on all instances in a database is a database checkpoint. Thread checkpoints occur in the following situations: - Consistent database shutdown - ALTER SYSTEM CHECKPOINT statement - Online redo log switch - ALTER DATABASE BEGIN BACKUP statement - Tablespace and data file checkpoints The database writes to disk all buffers modified by redo before a specific target. A tablespace checkpoint is a set of data file checkpoints, one for each data file in the tablespace. These checkpoints occur in a variety of situations, including making a tablespace read-only or taking it offline normal, shrinking a data file, or executing ALTER TABLESPACE BEGIN BACKUP. - Incremental checkpoints An incremental checkpoint is a type of thread checkpoint partly intended to avoid writing large numbers of blocks at online redo log switches. DBW checks at least every three seconds to determine whether it has work to do. When DBW writes dirty buffers, it advances the checkpoint position, causing CKPT to write the checkpoint position to the control file, but not to the data file

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