Background writer (bgwriter)
Also called: bgwriter, background writer process
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.
What this means
Trickles dirty pages out to disk a little ahead of demand, so when a backend needs a free page to work with, it usually finds an already-clean one instead of stopping to write a dirty page itself. It's the checkpointer's gentler sibling, always working a bit, never in bursts.
Why it matters operationally
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.