Hello Devlopers I was debugging the source code of mariadb. My query was MariaDB [sachin]> create table pro2(abc int primary key,xyz int , ass int ,unique(xyz,ass))engine=myisam; In table2myisam function of file ha_myisam.cc i found that we are allocating more memory for keysegments if (!(my_multi_malloc(MYF(MY_WME), recinfo_out, (share->fields * 2 + 2) * sizeof(MI_COLUMNDEF), keydef_out, share->keys * sizeof(MI_KEYDEF), &keyseg, (share->key_parts + share->keys) * sizeof(HA_KEYSEG), ^ here why this NullS))) And we donot use these extra key segments because suceeding for loop use only total number of share->key_parts keysegments. And same in ha_maria file.Is this a bug or I am missing something Regards sachin