Read issue in MongoDB asynchronous replication

I'm new to MongoDB. I created a Java app using Mo开发者_运维技巧ngoDB as database. I configured 3 servers in a replica set. my pseudo code: {

createUser getUser updateUser

}

Here createUser creates the user successfully but getUser fails to return that user in somtimes.

when I analysed it is due to the data replication latency.

How can I overcome this issue?

is there anyway to replicate data immediately when it is created?

is there any other way to get user without fail?

Thx in advance!

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If you are certain that the issue is due to replication latency, one thing you can do is make sure your writes are safe and using the w flag. That way, MongoDB will wait until data is replicated to at least n nodes before returning. You can do this from the client driver as well.

MongoDB getLastError

Are you reading with slaveOk=True ? If you read from the ReplicaSet Primary, this shouldn't be an issue either.

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The slaveOk property is now known as ReadPreference (.SECONDARY in this case) in newer Mongo Java driver versions. This can be set at the Mongo/DB/Collection level. Note that when you set ReadPreference at these levels, it applies for all callers (i.e. these objects are shared across threads).

Another approach is to try the ReadPreference.SECONDARY and if it fails, try without it and go to the master. This logic can be isolated to your repository layer, so the service layer doesn't have to deal with it. If you are doing this, you may want to set the ReadPreference at the DBQuery object, which is on a per-use basis.

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I am not familiar with Java driver, but there are w and j options.

The w option confirms that write operations have replicated to the specified number of replica set members, including the primary.

The j will confirm the write operation only after it has written the operation to the journal.

It looks like you need to use WriteConcern.