PostgreSQL version:

wal_writer_delay

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.

Recommendations

Defines the maximum data (in time) that can be lost if synchronous_commit=off and the database shuts down. Because of long transactions, actual data lost can be up to twice this time. Has no effect if synchronous_commit=on. If you are going to turn synchronous_commit=off server-wide, you should probably lower this to prevent too much data loss.

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