+
+-- Retention: This field indicates how much time must pass before an inactive
+-- list entry should be scrubbed. Null indicates retain forever.
+-- other values include "x day(s)", "x month(s)", "x year(s)". So,
+-- for example, a user on the white list may have its retention set
+-- to say 1 year and when mapsscrub runs, if last_hit is older than
+-- a year the whitelist entry would be removed. If, however,
+-- retention is null then the record is kept forever. This is useful
+-- for the null and black lists where one might want to insure that
+-- a particular domain (e.g. @talentburst.com) will never come off
+-- of the nulllist.
+ retention varchar (40),