bounded-collections.md

When declaring a collection type for a table column, you can limit either the number of elements or the total binary size of the collection. During query processing, Vertica always reserves the maximum memory needed for the column, based on either the element count or the binary size. If this size is much larger than your data actually requires, setting one of these limits can improve query performance by reducing the amount of memory that must be reserved for the column.

You can change the bounds of a collection, including changing between bounded and unbounded collections, by casting. See Casting.

A bounded collection specifies a maximum element count. A value in a bounded collection column may contain fewer elements, but it may not contain more. Any attempt to insert more elements into a bounded collection than the declared maximum is an error. A bounded collection has a binary size that is the product of the data-type size and the maximum number of elements, possibly rounded up.

An unbounded collection specifies a binary size in bytes, explicitly or implicitly. It may contain as many elements as can fit in that binary size.