Improving column compression
If you see slow performance or a large storage footprint with your FLOAT data, evaluate the data and your business needs to see if it can be contained in a NUMERIC column with a precision of 18 digits or less. Converting a FLOAT column to a NUMERIC column can improve data compression, reduce the ondisk size of your database, and improve performance of queries on that column.
When you define a NUMERIC data type, you specify the precision and the scale; NUMERIC data are exact representations of data. FLOAT data types represent variable precision and approximate values; they take up more space in the database.
Converting FLOAT columns to NUMERIC columns is most effective when:

NUMERIC precision is 18 digits or less. Performance of NUMERIC data is finetuned for the common case of 18 digits of precision. Vertica recommends converting FLOAT columns to NUMERIC columns only if they require precision of 18 digits or less.

FLOAT precision is bounded, and the values will all fall within a specified precision for a NUMERIC column. One example is monetary values like product prices or financial transaction amounts. For example, a column defined as NUMERIC(11,2) can accommodate prices from 0 to a few million dollars and can store cents, and compresses more efficiently than a FLOAT column.
If you try to load a value into a NUMERIC column that exceeds the specified precision, Vertica returns an error and does not load the data. If you assign a value with more decimal digits than the specified scale, the value is rounded to match the specified scale and stored in that column.