Checkpointer
Also called: checkpointer process, CKPT
The checkpointer is the background process that performs checkpoints: it flushes all dirty shared buffers to disk and writes a checkpoint WAL record, giving crash recovery a bounded place to start. It also absorbs fsync requests handed off by backends and spreads its writes over time to avoid I/O spikes.
What this means
The background process that carries out checkpoints, flushing all the dirty pages in memory out to disk and writing a checkpoint mark so crash recovery has a bounded place to start. It spreads its writes out over time on purpose, so a checkpoint doesn't land as one big I/O spike.
Why it matters operationally
Checkpoint behavior is one of the biggest I/O levers in PostgreSQL. Tuning checkpoint_timeout, max_wal_size, and checkpoint_completion_target changes how often and how gently the checkpointer writes, the difference between smooth and spiky disk load.