Specifies how often the WAL writer flushes WAL. 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. If
wal_writer_flush_after is set to
0 then WAL data is flushed immediately. The default is
1MB. This parameter can only be set in the postgresql.conf file or on the server command line.