Deletion Marker Mergeout

When you delete data from the database, Vertica does not remove it. Instead, it marks the data as deleted. Using many DELETE statements to mark a small number of rows relative to the size of a table can result in creating many small containers—delete vectors—to hold data marked for deletion. Each delete vector container consumes resources, so a large number of such containers can adversely impact performance, especially during recovery.

After the Tuple Mover performs a mergeout, it looks for deletion marker containers that hold few entries. If such containers exist, the Tuple Mover merges them together into a single, larger container. This process helps lower the overhead of tracking deleted data by freeing resources used by multiple, individual containers. The Tuple Mover does not purge or otherwise affect the deleted data, but consolidates delete vectors for greater efficiency.