What is the difference between checkpointer and background writer?

Checkpointer and Background Writer are two different processes in PostgreSQL that handle writing data to disk, but with different goals and mechanisms.

• Checkpointer is responsible for creating checkpoints. It periodically writes all changed pages from the buffer to persistent storage to reduce recovery time after a crash. The checkpoint guarantees that all data up to a certain point in time is saved to disk.

• Background Writer works continuously and gradually writes changed pages from the buffer to disk to reduce system load during checkpoints. Its task is to keep the buffer in a clean state so that during a checkpoint, not too much data needs to be written at once.

In summary:

• Checkpointer — periodic, large data flushes to ensure integrity.
• Background Writer — constant, background buffer cleaning to evenly distribute load.