Specifies how often the WAL writer flushes WAL. After flushing WAL it sleeps for
wal_writer_delay milliseconds, unless woken up by an asynchronously committing transaction. If the last flush happened less than
wal_writer_delay milliseconds ago and less than wal_writer_flush_after bytes of WAL have been produced since, then WAL is only written to the operating system, not flushed to disk. The default value is 200 milliseconds (
200ms). Note that on many systems, the effective resolution of sleep delays is 10 milliseconds; setting
wal_writer_delay to a value that is not a multiple of 10 might have the same results as setting it to the next higher multiple of 10. This parameter can only be set in the postgresql.conf file or on the server command line.