In which situations does the Database Writer process (DBWn) write to data files?

During RMAN recovery, especially when applying changes to data blocks in memory or writing recovered blocks, DBWn is invoked to write these blocks to the data files.

When a user process commits a transaction, the LGWR (Log Writer) process primarily writes redo records to the online redo log files, not DBWn directly writing data blocks.

When a tablespace is taken offline or made read-only, DBWn must write all dirty blocks belonging to that tablespace to disk to ensure data consistency before the state change.

PMON (Process Monitor) cleans up failed user processes and their resources, it does not clean up dirty buffers in the database buffer cache; that is DBWn's responsibility.

While the inability to find clean buffers is a symptom that leads to DBWn activity, DBWn typically writes proactively based on dirty buffer thresholds or checkpoints, *before* clean buffers become truly scarce or 'not found easily' to prevent performance degradation.