myisampack — Generate Compressed, Read-Only MyISAM Tables The number of integer columns that do not occupy the full byte range of their type. These are changed to a smaller type. For example, a  BIGINT  column (eight bytes) can be stored as a  TINYINT  column (one byte) if all its values are in the range from  -128  to  127 . The number of decimal columns that are stored with leading spaces. In this case, each value contains a count for the number of leading spaces. The number of columns that have a lot of trailing spaces. In this case, each value contains a count for the number of trailing spaces. The column had only a small number of different values, which were converted to an  ENUM  before Huffman compression. The number of columns for which all values are zero. The initial number of Huffman trees. The number of distinct Huffman trees left after joining trees to save some header space. After a table has been compressed, the  Field  lines displayed by  myisamchk -dvv  include additional information about each column: The data type. The value may contain any of the following descriptors: All rows have the same value. Do not store endspace. Do not store endspace and do not do endspace compression for all values. Do not store endspace. Do not store empty values. The column was converted to an  ENUM . 585 • Type • constant • no endspace • no endspace, not_always • no endspace, no empty • table-lookup • pre-space • end-space • table-lookup • zero • Original trees • After join