Lock compatibility matrix

Hi there,

following discussion in -patches about lock compatibility matrix,
posted by Teodor, we have another matrix 
http://mira.sai.msu.su/~megera/pgsql/lockmatrix/c2.html
Besides formatting improvements, it has addtional lock with
temporary name UPDATE EXCLUSIVE (UE), which is the same as 
EXCLUSIVE, but doesn't conflicts with SHARE UPDATE EXCLUSIVE (SUE),
which aquired by VACUUM and autovacuum. The reason for this is that
at present we have no lock mode, which doesn't conflicts with *vacuum.
The problem was described in thread 
http://archives.postgresql.org/pgsql-general/2006-12/msg01476.php

What is the reason why we don't have such lock ?
    Regards,        Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83