Database Reference
In-Depth Information
Immediate and eventual consistency
In the master-follower scenario, we can say that reads from the master provide
immediate
consistency
. Immediate consistency is simply a guarantee that, as soon as a piece of data is
written successfully, it will be available to clients who are reading that data. There is no
delay between writing data and being able to read it.
On the other hand, reads from the followers provide
eventual consistency
. Eventual con-
sistency means that, once the data is successfully written, it will, at some point in the fu-
ture, become available for reads. There is no guarantee of how soon it will become avail-
able; the only guarantee is that the time will eventually come. Of course, in a healthy pro-
duction deployment, the delay between write and read availability is typically in the order
of milliseconds, but we have no guarantee that it won't be much longer.
