Physical BI size vs logical BI size and backups

Posted by James Palmer on 19-Dec-2016 10:59

Just a question out of interest more than anything as we are committed to sorting this out whether or not it makes a difference. 

Somehow one of our clients has managed to get the BI on their DB set to 4 fixed 2GB extents and a variable extent. I'd be surprised if the BI ever fills the first extent on a bad day. 

The issue is that whenever the backups kick in they are experiencing a freeze, in keeping with the backup backing up the BI. This is even happening just after a truncate. The question is, is this freeze going to be longer in their situation of around 8GB of physical BI compared to if they just had a variable extent of a few MB, shortly after a truncate? 

Hope I've explained that well enough. 

10.2B08 on Windows. 

All Replies

Posted by mfurgal on 19-Dec-2016 11:08

James:

Depending on the version different things happen.

In all versions, the most online backup will do will be to backup up to the high water mark of the file.  So if there is 8 GB of fixed storage allocated, but the high water mark is 1 GB, then only 1 GB will be backed up.  During the backup of this 1 GB, all update activity will be paused.

In version 11 (can’t remember the specific version) online backup only backs up ACTIVE clusters.  This means any BI Cluster that has notes needed for Crash Recovery.  So in the same case, where there is 8 GB of fixed storage, 1 GB of used storage (High Water Mark), but only 10 ACTIVE cluster which are 16 MB each, this means that online backup would only backup of 160 MB of BI space, hence the time updates are paused are the times it takes to backup the 160 MB.

Mike
-- 
Mike Furgal
Director – Database and Pro2 Services
PROGRESS Bravepoint
678-225-6331 (office)
617-803-2870 (cell)


Posted by kirchner on 19-Dec-2016 11:09

James, yes. The BI is copied in its entirety even if it is mostly empty.

Starting in OE 11.something there is a new feature that only copies the active BI portion. There's been a severe bug around this feature but I think in 11.5+ it is safe to use.

Posted by George Potemkin on 19-Dec-2016 11:15

> Starting in OE 11.something there is a new feature that only copies the active BI portion.

Since 11.2:

Dumped %J active BI blocks. (16866)

"bibackup all" option restores the old behaviour (up to HWM).

Only probkup with the -norecovery option will dump all BI extents.

Posted by Rob Fitzpatrick on 19-Dec-2016 11:18

The message may have been in the 11.2 promsgs but the feature was enabled in 11.3.  

As has been noted, you shouldn't use the default in 11.3 and 11.4.  Those who are on those releases should add "bibackup all" to their probkup command line.  The bug is fixed in 11.5+.

Posted by James Palmer on 19-Dec-2016 11:37

Thanks everyone. Confirms we do need to do the maintenance on the BI at some stage.

The good news is that it's highlighted other issues to the right people. They are backing up every 3 hours to minimise data loss risk, but the backups were taking 3+ hours to complete, and combined with a freeze on the BI backup it was causing trouble. Further investigations confirm they weren't deleting the old .bck file first. That reduced backup time to less than 30 minutes. It also highlighted that they aren't running AI. And I've finally managed to convince the people that matter that this is a bad thing. Happy Christmas everyone!!

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