Re: latch-free SCN scheme (10.1.0.3)

I notice that prior to 10g, alert.log only says "SCN scheme 2" ("Picked latch-free" is not there). Not sure about its meaning. Probably a lazy way to say "Picked *mostly* latch free SCN ..." as the latch name suggests.

In RAC, you still see that line immediately after startup. But when the database is opened, you see

Tue Feb 15 14:08:37 2005
ALTER DATABASE OPEN
This instance was first to open
Picked Lamport scheme to generate SCNs

while the non-RAC database only says "alter database open".

If I keep running
select gets, dbms_flashback.get_system_change_number from v$latch where name = 'mostly latch-free SCN';
I see that when SCN increments by 1, that latch get increments by 1; if SCN goes up by 2 or 3 or more, latch get also goes up but by a smaller number.

I don't know what zero-copy redo is either but it looks like a 10g thing, and is controlled by _log_private_parallelism. There're also underscore parameters related to latch-free SCNs, even back to 8i.

If you ever find an answer, please let us know.

Yong Huang Received on Tue Feb 15 2005 - 16:42:34 CST