Comments on: “change tracking state change latch” http://www.pythian.com/news/317/change-tracking-state-change-latch/ News and views from Pythian DBAs Fri, 10 Feb 2012 13:01:25 +0000 hourly 1 http://wordpress.org/?v=3.0.4 By: Alex Gorbachev http://www.pythian.com/news/317/change-tracking-state-change-latch/#comment-10748 Alex Gorbachev Fri, 15 Dec 2006 14:37:17 +0000 http://www.pythian.com/blogs/317/change-tracking-state-change-latch#comment-10748 That's an interesting idea Jonathan. Correct me if I'm wrong, but latches are to protect local instance memory structures so for RAC I would expect so kind of global enqueue. No? Unfortunately, I've been extremely busy last days to put any time around it but I found out (thanks to one person contacted me from Oracle) that mechanism to pass block changes is indeed similar to a log buffer but it's going directly from session processes and not DBWR. To be researched... That’s an interesting idea Jonathan. Correct me if I’m wrong, but latches are to protect local instance memory structures so for RAC I would expect so kind of global enqueue. No?
Unfortunately, I’ve been extremely busy last days to put any time around it but I found out (thanks to one person contacted me from Oracle) that mechanism to pass block changes is indeed similar to a log buffer but it’s going directly from session processes and not DBWR. To be researched…

]]> By: Jonathan Lewis http://www.pythian.com/news/317/change-tracking-state-change-latch/#comment-10729 Jonathan Lewis Fri, 15 Dec 2006 12:51:04 +0000 http://www.pythian.com/blogs/317/change-tracking-state-change-latch#comment-10729 Alex, just an idle thought about the latch: might it be there for RAC systems to ensure that no two RAC systems end up "owning" the same bitmaps in the change tracking log ? Alex, just an idle thought about the latch: might it be there for RAC systems to ensure that no two RAC systems end up “owning” the same bitmaps in the change tracking log ?

]]> By: Alex Gorbachev http://www.pythian.com/news/317/change-tracking-state-change-latch/#comment-8708 Alex Gorbachev Mon, 27 Nov 2006 14:23:41 +0000 http://www.pythian.com/blogs/317/change-tracking-state-change-latch#comment-8708 Fairlie, Thanks for correction - it's definitely v$backup_datafile. Indeed, according to this <a href="http://wedonotuse.blogspot.com/2006/11/how-cia-stole-oracle-from-russians.html" rel="nofollow">theory</a> I should be more comfortable with X$ rather than V$. ;-) Regarding _bct_bitmaps_per_file=8 - I guess it's 8 because CTWR cleans up 8th past version and older. As I mentioned, I'll check how it works if I change this parameter. Fairlie,
Thanks for correction – it’s definitely v$backup_datafile. Indeed, according to this theory I should be more comfortable with X$ rather than V$. ;-)
Regarding _bct_bitmaps_per_file=8 – I guess it’s 8 because CTWR cleans up 8th past version and older. As I mentioned, I’ll check how it works if I change this parameter.

]]> By: Fairlie http://www.pythian.com/news/317/change-tracking-state-change-latch/#comment-8629 Fairlie Mon, 27 Nov 2006 01:50:41 +0000 http://www.pythian.com/blogs/317/change-tracking-state-change-latch#comment-8629 Just skimmed through your presentation. Needless to say it is very informative and excellent. • I think the number of bitmaps to store for each datafile is 8 because it is governed by _bct_bitmaps_per_file. I wonder what would happen if u were to change it to 0 • On Slide 26 you mention v$datafile_backup. The view name is v$backup_datafile. (It’s good to know that I am not the only person who gets confused with these views  ) • I remember in earlier versions there was a bug where the direct load used to fail when using BCT. I believe this has been fixed. One of the current issues I know of is Bug 5606208 BLOCK CHANGE TRACKING (BCT) LOST AFTER SWITCHOVER Just skimmed through your presentation. Needless to say it is very informative and excellent.

• I think the number of bitmaps to store for each datafile is 8 because it is governed by _bct_bitmaps_per_file. I wonder what would happen if u were to change it to 0

• On Slide 26 you mention v$datafile_backup. The view name is v$backup_datafile. (It’s good to know that I am not the only person who gets confused with these views  )

• I remember in earlier versions there was a bug where the direct load used to fail when using BCT. I believe this has been fixed.

One of the current issues I know of is
Bug 5606208
BLOCK CHANGE TRACKING (BCT) LOST AFTER SWITCHOVER

]]>