In this section, we will take a look at how failovers can be handled. We will also see how nodes can be added to and removed from a Postgres-XC setup in a safe and reliable way.
If you execute a query in Postgres-XC, it might be dispatched to many different nodes inside the cluster. For example, performing a sequential scan on a highly partitioned table will involve many different nodes. The question now is: what happens if one or some of those data nodes are down?
The answer is pretty simple—Postgres-XC will not be able to perform the requests by making use of failed nodes. This can result in a problem for both reads and writes. A query trying to fetch from a failed node will return an error indicating that no connection is available. At this point, Postgres-XC is not yet very fault tolerant. Hopefully, this will change in the future.
For you as a user, this means that if you are running Postgres-XC, you have to come up with a proper...