wal_writer_delay
No restart — takes effect on reloadtime (ms)
How often the WAL writer flushes WAL in the background.
What it does
The WAL writer periodically flushes accumulated WAL so backends — especially with synchronous_commit = off — don't each have to flush at commit. wal_writer_delay sets how often it runs.
How to tune it
The default 200 ms suits most setups. It mainly matters with synchronous_commit = off, where it bounds how much recent WAL could be lost on a crash. Lower it if you want a tighter loss window; raise it to reduce wakeups on idle systems.