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postgresqldrupalcharacterbyte

What is the maximum possible size of VARCHAR(255)?

On Drupal documentation page (https://www.drupal.org/docs/7/api/schema-api/data-types/varchar) I read:

Make sure you are aware of the effects of a multi-byte character set. VARCHAR(255) stores 255 characters, which may be more than 255 bytes.

So I got curious what is the maximum possible size of 255 characters?

Solution

  • According to RFC 2279, the highest possible character (code point 0x7FFF FFFF) could be represented by 6 bytes. The highest possible code point you can represent in PostgreSQL is 0x10FFFF, which occupies 4 bytes:

    SELECT E'\U0010FFFF';

 ?column? 
══════════
 
(1 row)

SELECT E'\U00110000';
ERROR:  invalid Unicode escape value at or near "\U00110000"
LINE 1: SELECT E'\U00110000';
                 ^

SELECT CAST(E'\U0010FFFF' AS bytea);

   bytea    
════════════
 \xf48fbfbf
(1 row)

    So you are on the safe side if you assume an upper limit of 4 bytes per character.