Summing values from database

I have a process that sample about 16 status variables related to 
database connectivity and stores them in the rrd.  For example I have 
track the active and idle connections to two different databases.  What 
I'd like to do is add active to idle to make total and then display 
total and active on the same graph.  Something like:

datasource  flood-active
     ds-source   =   "exec:0:%home-dir%/bin/tomcat-db-conn.pl %server% 
'%tomcat-url%'"
     desc        =   "Active Connections to FLOOD."
     rrd-ds-type     =   GAUGE

datasource  flood-idle
     ds-source   =   "exec:1:%home-dir%/bin/tomcat-db-conn.pl %server% 
'%tomcat-url%'"
     desc        =   "Idle Connections to FLOOD."
     rrd-ds-type     =   GAUGE

datasource flood-max
     ds-source   =   "exec:2:%home-dir%/bin/tomcat-db-conn.pl %server% 
'%tomcat-url%'"
     rrd-ds-type = GAUGE

datasource flood-min
     ds-source   =   "exec:3:%home-dir%/bin/tomcat-db-conn.pl %server% 
'%tomcat-url%'"
     rrd-ds-type = GAUGE

datasource flood-total
     ds-source = "flood-idle, flood-active, +"

It seems that it should be straightforward but I cannot figure it out. 
mtargets looked promising but it seems to only allow for one combined 
value per graph.

-- 
Stephen Carville <[email protected]>
Unix and Network Admin
Nationwide Totalflood
6033 W. Century Blvd
Los Angeles, CA 90045
310-342-3602


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