Re: How to calculate the optimal size for undo segments

Hi!

I'm just wondering, how is this undo_retention measuring in seconds implemented internally.

If a wrap occurs in manual undo mode, first the transaction table in rollback segment header is checked whether there are any active transactions in next extent, if not the next extent can taken into use (of course there are special cases such extending an shrinking to optimal). But this wrap only checks for active transactions.

Now with undo_retention set in seconds, where does the timing information come from? AFAIK, so far, there is no timestamps saved in undo headers. So is there some kind of mapping of SCNs and timestamps done in SGA or what?

Is there any new events regarding undo segment activities in addition to 10016,10017,10048 in 9i?

Tanel. Received on Fri Mar 07 2003 - 07:56:18 CST