Also called: bgwriter, background writer process
In plain English
The background writer trickles dirty shared buffers out to disk ahead of demand, so that when a backend needs a free buffer it usually finds a clean one instead of stalling to write a dirty page itself. It is the checkpointer’s lighter-touch sibling, working continuously rather than in bursts.
Why it matters
A well-tuned bgwriter shifts write work off your query backends, smoothing latency. bgwriter_delay and bgwriter_lru_maxpages control how aggressively it pre-cleans buffers.