Updating the VoltDB software is very simple. However, you must make sure you perform this step at the right stage in the upgrade process, as described in the following sections. The product comes as a .tar.gz file. When the time comes to upgrade the software, you unpack the tar file and move the resulting folder to replace your current installation. For example, if you have the VoltDB software installed as /var/voltdb, the software installation looks like the following, where you delete the previous version and replace it with the new one:

$ tar -zxvf voltdb-ent-n.n.n-xxxx.tar.gz -C /var
$ cd /var
$ rm -vr voltdb
$ mv voltdb-ent-n.n.n-xxxx voltdb

Remember, when upgrading an existing installation with a running database, you need to upgrade both the software and the database itself. Which means you must make sure you perform the update steps in the correct order. The following sections explain the different options for updating existing installations, including at what stage in the process you should replace the software.

Upgrading the VoltDB software on a single database cluster is easy. All you need to do is perform an orderly shutdown saving a final snapshot, upgrade the VoltDB software on all servers in the cluster, then restart the database. The steps to perform this procedure are:

This process works for any recent (V6.8 or later) release of VoltDB.

Normally, when upgrading the VoltDB software, you must shutdown the cluster (for example, with the voltadmin shutdown --save command) and restart the entire cluster using the new software. Downtime can be avoided by performing an in-service upgrade. An in-service upgrade allows a K-safe cluster to be upgraded one node at a time, rather than the entire cluster all at once. This means the cluster, and the business processes it supports, remain available throughout the upgrade procedure.

The requirements for performing an in-service upgrade are:

To perform an in-service upgrade on bare metal servers, you upgrade the VoltDB software on each node consecutively. Specifically:

During the upgrade process, you can determine which nodes have been updated using the @SystemInformation system procedure with the OVERVIEW selector and looking for the VERSION keyword. For example, in the following command output, the first column is the host ID and the last column is the currently installed software version for that host. Once all hosts report using the upgraded software version, the upgrade is complete.

$ echo "exec @SystemInformation overview" | sqlcmd | grep VERSION
       2 VERSION                   13.1.2                                                                                     
       1 VERSION                   13.1.2                                                                                     
       0 VERSION                   13.1.3  

Until the upgrade process is complete, all nodes in the cluster maintain the functionality of the lower version, even for those nodes that have already upgraded to the higher version software. Once the upgrade is complete and all nodes are running on the newer version, the cluster switches to operating with the higher version functionality. In other words, if the new software contains any new function or behavior, that feature will not be accessible until the entire in-service upgrade process is complete.

If the upgrade fails for any reason, or you choose to stop the upgrade midway, you can revert to the original version by reversing the process: removing a node that has been upgraded, replace the VoltDB software with the original version, rejoin the node and repeat for all nodes that were upgraded. Once the upgrade process is complete, the in-service upgrade is over. At which point, you can longer return to the previous version through an in-service upgrade and must perform a full cluster restart to downgrade.

It is also possible to upgrade the VoltDB software using cross data center replication (XDCR), by simply shutting down, upgrading, and then re-initalizing each cluster, one at a time. This process requires no downtime, assuming your client applications are already designed to switch between the active clusters.

Use of XDCR for upgrading the VoltDB software is easiest if you are already using XDCR because it does not require any additional hardware or reconfiguration. The following instructions assume that is the case. Of course, you could also create a new cluster and establish XDCR replication between the old and new clusters just for the purpose of upgrading VoltDB. The steps for the upgrade outlined in the following sections are the same. But first you must establish the cross data center replication between the two (or more) clusters. See the chapter on Database Replication in the Using VoltDB manual for instructions on completing this initial step.

Once you have two clusters actively replicating data with XCDCR (let's call them clusters A and B), the steps for upgrading the VoltDB software on the clusters is as follows:

Note that since you are upgrading the software, you must create a new instance after the upgrade (step #3). When upgrading the software, you cannot recover the database using just the voltdb start command; you must use voltdb init --force first to create a new instance and then reload the existing data from the running cluster B.

Also, be sure all data has been copied to the upgraded cluster A after step #4 and before proceeding to upgrade the second cluster. You can do this by checking the @Statistics system procedure selector DRCONSUMER on cluster A. Once the DRCONSUMER statistics State column changes to "RECEIVE", you know the two clusters are properly synchronized and you can proceed to step #5.