LGWR special commit/checkpoint records

From: Doug Carter <dcarter_at_tui.com.au>
Date: Fri, 1 May 1998 16:34:26 +1000
Message-ID: <6ibqdg$n7b$1@reader1.reader.news.ozemail.net>

This is for the more technical of you. I had a rather good question from a database user today that I would like verified. (Replies direct to me if possible).

He understood that you can recover to a point in time using redo data. What he wanted to know was in what format this timestamp is kept. i.e. did it include Timezone information or without etc.

I know that the redo log contains two special records - written at commit and checkpoints, and that each redo log block contains an 18 byte header. I assume that the timestamp sits in the special records for obvious reasons.

Now the normal date datatype in oracle is stored in a 7 byte field as an excess 100 number. This would seem unsuitable for something which is used for a point in time recovery - especially around day light savings!

I think I heard once that oracle can use a value of seconds after a point in time around 1972 (sorry, can not remember the correct term for it, but it is not Oracle specific) based on GMT. I assume that Oracle uses this.

Can someone please fill in the assumptions?

Much appreciated,

Doug Carter
Database Administrator
TUI Consulting Received on Fri May 01 1998 - 01:34:26 CDT