I'm in the midst of a similar project. I used the following script to determine shared memory usage on Solaris hosts for Sybase and Oracle. I ran this several times a day on each host, though the numbers really didn't change much. I found this to be much better than utilizing what the DB was configured to use, as this will show what the DB actually utilizes.

if ipcs -ma | grep sybase > /dev/null ; then
  echo Sybase
  ipcs -ma  | grep sybase | awk '{ T+=($10/1024/1024) } END { print T }'
elif ipcs -ma | grep oracle > /dev/null ; then
  echo Oracle
  ipcs -ma  | grep oracle | awk '{ T+=($10/1024/1024) } END { print T }'
fi