Why DBvisualizer and Vsql treat the length of a special character in different way?

What is the default character encoding on the Operating System you are running VSQL from?

Acisneros,
One thing I wanted to note is that in your supplied examples you did octel_length of two different strings.
DBVis = select octet_length('¿hóla'); = 5
VSQL = select octet_length('hóla');

That aside, in my vsql 9.3 for the 'hóla' string I get 5, same in DBVis 12 on Windows 10 with Vertica JDBC 9.3 driver. So for me both report the same octet length of 5.

I do see the error you see when inserting into the table, octet length 5 too long for varchar(4). This error is correct. Please refer to the following two Vertica doc pages and the sections I've extracted related to what you are seeing. Although not intuitive, when you define a varchar the length you define is octets not characters. So for a 5 octet string you'd need varchar(5). If you plan on loading a lot of foreign characters you may need to increase the varchar size to accommodate.

https://www.vertica.com/docs/10.1.x/HTML/Content/Authoring/SQLReferenceManual/DataTypes/CharacterDataTypes.htm
Setting Maximum Length
When you define character columns, specify the maximum size of any string to be stored in a column. For example, to store strings up to 24 octets in length, use one of the following definitions:

CHAR(24) /* fixed-length /
VARCHAR(24) / variable-length */
The maximum length parameter for VARCHAR and CHAR data types refers to the number of octets that can be stored in that field, not the number of characters (Unicode code points). When using multibyte UTF-8 characters, the fields must be sized to accommodate from 1 to 4 octets per character, depending on the data. If the data loaded into a VARCHAR/CHAR column exceeds the specified maximum size for that column, data is truncated on UTF-8 character boundaries to fit within the specified size.

https://www.vertica.com/docs/10.1.x/HTML/Content/Authoring/SQLReferenceManual/Functions/String/OCTET_LENGTH.htm
Parameters
expression
(CHAR or VARCHAR or BINARY or VARBINARY) is the string to measure.

Notes
If the data type of expression is a CHAR, VARCHAR or VARBINARY, the result is the same as the actual length of expression in octets. For CHAR, the length does not include any trailing spaces.

I hope it helps,