By default, the scaling factor only has an effect when Vertica rebalances the database. During rebalancing, nodes break the projection segments they contain into storage containers which they can quickly move to other nodes.

This process is more efficient than re-segmenting the entire projection (in particular, less free disk space is required), but it still has significant overhead, since storage containers have to be separated into local segments, some of which are then transferred to other nodes. This overhead is not a problem if you rarely add or remove nodes from your database.

However, if your database is growing rapidly and is constantly busy, you may find the process of adding nodes becomes disruptive. In this case, you can enable local segmentation, which tells Vertica to always segment its data based on the scaling factor, so the data is always broken into containers that are easily moved. Having the data segmented in this way dramatically speeds up the process of adding or removing nodes, since the data is always in a state that can be quickly relocated to another node. The rebalancing process that Vertica performs after adding or removing a node just has to decide which storage containers to relocate, instead of first having to first break the data into storage containers.

Local data segmentation increases the number of storage containers stored on each node. This is not an issue unless a table contains many partitions. For example, if the table is partitioned by day and contains one or more years. If local data segmentation is enabled, then each of these table partitions is broken into multiple local storage segments, which potentially results in a huge number of files which can lead to ROS "pushback." Consider your table partitions and the effect enabling local data segmentation may have before enabling the feature.