But since I'm already updating some values in the database automatically every 30 seconds, I've figured out it would be nice to also distribute curation reward every 30 seconds. In other words every investor's profit balance will slightly increase every 30 seconds, even if no new vote requests payments are coming.

That's not where 30 seconds comes from. You don't seem to be following me at all. This is just good programming practice. It has nothing to do with steem. It could be any software that @tipu is operating against. @tipu is what we're discussing.

You're right though. I should take into account the block update. Taking into account block update (every 3 seconds), this means that that conversion values persisted will only actually be good for 3 seconds. Which also means that only conversion values read within 3 seconds of the conversion being persisted will actually be accurate. That's the best case scenario (values are persisted nearly on or right after a block update). It's possible conversion values persisted just before (maybe 1 second) a block update. This would cause persisted conversion values to only be good for one second which would be your worst case scenario. IMHO, those are ideal conditions for on-the-fly conversion. Instead of persisting it.

But since I'm already updating some values in the database automatically every 30 seconds

Now that I reread this, it seems other values are affecting things as well. Updating values every 30 seconds turns records/documents/whatever into index entries because they can only live for 30 seconds. I think it's a good idea not to do this. Instead of updating the values every 30 seconds, store original values.