I created a PHP script that times how long an insert cursor takes to insert data per each write concern.

See results below: (write concerns are based off of the PHP driver doc)

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Write concern: 0 : Fire and forget
Cursor return: 0.0001230240

Write concern: 1 : Write acknowledged by the primary only
Cursor return: 0.0548999310 <-- SLOWEST????

Write concern: 2 : Write confirmed in 2 secondaries
Cursor return: 0.0135748386

Write concern: 3 : Write confirmed in 3 secondaries
Cursor return: 0.0042228699

Write concern: majority : Write confirmed in the majority of secondaries
Cursor return: 0.0204229355

Write concern: j : write acknowledged by primary and the journal flushed to disk
Cursor return: 0.0119099617
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Do you know why I would see a much higher time in microseconds with write concern 1 (acknowledgement from the primary) compared to all others?