How can I use rs.slaveOK() on mongo shell?

Question

I have checked the official document many times, it dose has the rs.slaveOK() function there and also the shell-help document.

I can't use rs.slaveOK() even if the function really exist.(Error occur)

That is so weird. Why is that?

The shell try to indicate me that rs.slaveOK() is not a function when I type it.

Answer 1

Be careful! MongoDB functions are case sensitive:

rs.slaveOK() is not a function

rs.slaveOk() is the function you are looking for.

Answer 2

You would use rs.slaveOk() when your Mongodb is set up as a replicaset, and you wish to query one of the secondary nodes, rather than the primary. slaveOk is instructing the shell that its ok to return results from a secondary (rather than a primary) even though the results may not be entirely consistent with the primary.

I could be wrong, but it doesn't look like you are connected to a Mongodb which is configured as a replicaset, and if you are then I'm guessing that you are not connected to a secondary. Therefore the instruction to query a secondary makes no sense.