--syncdelay

This command line option specifies the number of seconds between data file flushes/syncs.

The MongoDB journal file flushes almost immediately, but data files are flushed lazily to optimize performance.

The default is 60 seconds.

A 0 setting means never, but is not recommended and should never be used with journaling enabled.

On Linux, longer settings will likely be ineffective unless /proc/sys/vm/dirty_expire_centisecs is adjusted also. Generally, set syncdelay to 4x the desired dirty_expire_centiseconds value.

If backgroundFlushing.average_ms is relatively large (>= 10,000 milliseconds), consider increasing this setting as well as dirty_expire_centiseconds.

Under extremely high write volume situations, a higher syncdelay value may result in more journal files as they cannot be rotated (deleted) as quickly.

--syncdelay

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