Code review comment for lp:~kfogel/launchpad/509194-506514-bug-heat-db-fixes

We talked to gmb and decided to let NULL represent "this bug's heat has never been updated", since that's consistent with what other timestamp fields in Launchpad do. We don't want to use CURRENT_TIMESTAMP because if for some reason the set-heat-on-bug-creation job fails, we want the hourly cron script that chooses bugs to update based on heat_last_updated to pick this one up, and if it claims its heat was recently updated it might get ignored.

We added a comment to comments.sql indicating this.

Thanks,
-Abel and Karl