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Hustler 9 posts Joined 12/15
24 Mar 2016
Teradata DSA online backup

Hi Everybody,
I have few questions around online backups.
Sol& Tools: Currently we are planning to use Teradata DSA(TDSA) solution with NetBackup  tool. The amount of data to be backed up is currently around say 10TB. Backing to disks not the tapes
** Abbreviations:
(TDSA)- Teradata Data stream architecture solution.
I knew some clients run online backups as they run ETL most of the time, What said is the explicit feature of the online backup. That being said, I am not clear of 2-3% change guideline (if I am not wrong where it explicitly says while running online backups there should not be more than 2-3% change at the whole database level)** Correct me if I am wrong/not exact**
DID ANYBODY HAD SEEN BACKUP FAILED OR ETL FAILED BCZ OF SPOOL SPACE EXCEEDED.” considering only 20-30% of total space is dbc spool space
As I understood it, while running online backup TDSA read the whole and create the check point and start writing to the disk solution, while at the same time users can do read and write (R&W) operations on the objects.
                The question here, 1. is  DSA copying all the objects and placing them in the spool?(I hope this is not what goes there, but if you say yes, what for 10TB backup assuming it is a full backup, how much space it take up form DBC spool?), OR
2. is Teradata keep the updates of any kind in a temporary table(which of course should go to spool)  which one happens and how 2-3% change thumb rule effects the spool? Or what is this guideline warning us towards? If you say yes for this 2nd after running any ETL during backup and if we query the object will TDATA gives us new updated values?
                Scenario: If the table name is “SMILING” before backup run and while running backup table name is updated to “TERRIFIED”. Will querying the table with TERRIFIED return the values? If you say we don’t rename tables so often, if the update is at row level will we get the updated values while backup is still is in running status.
3. AS TERADATA already had the data compressed while storing on it’s disk, is it true that TDSA still compresses the data while backing it to disk backups.(if it recompresses what is the expected ratio?)
**I appreciate if you could attach any standard documents as a reference for any comments**
Hoping for a good advice, Please do ask me if I forgot to mention any details.
Thanks in advance. 

Thanks, Komal
seven11 26 posts Joined 12/09
02 May 2016

Online Archive is about the same under DSA as it is ARC, there is a Teradata Orange Book on the subject avaiable via "Teradata at your service"
Online Archive will take more resources from all over the place

  1. Online Archive is initiated across one or more objects
  2. lock is placed across all of the required objects to create a sync-point
  3. a subtable is created for each of the tables is created within its containing database
  4. lock is released once the sync-point is fully established
  5. before a change to a row is commited to the base table a before image is written to the sub-table
  6. base table is backed up
  7. associated sub-table is backed up

While I'm sure spool it being used all over the place I would think the size of the sub-table is probably going to be of more concen
How much space will it take up?  While 20% additional is bandied about the two major factors are going to be duration of the backup process and the rate of change in that window, theoretically the sub-table could become bigger than the base if allowed to.
On a restore the base table is restored and then sub-table, using the sub-table the before images are applied back to the base tables so the object/set is back to the state when the sync-point was established.
Not sure what you are asking in your second point
There are mutltiple types of compression within Teradata (again there is an Orange Book on compression which might be handy) MVC & ALC stay compressed with ARC and DSA, while for BLC;
- for ARC the database will uncompress the data before sending it out
- for DSA the BLC will be kept compressed

ToddAWalter 316 posts Joined 10/11
03 May 2016

No spool is used during DSA backups. The tables are not spooled, they are copied directly out to the backup environment. The changes are stored in a subtable as part of the permanent table until such time as the backup of both the table and change log are sucessfully backed up to the backup environment.
The guideline for a small change percent is twofold:
- The log will get large if a large amount of change is applied while the backup is going on, increasing the perm space needed to store the table.
- A restore will take longer to apply the change logs, especially if online backups are done for a number of days.
When the change percent gets a lot higher, it is cheaper and quicker to backup the table rather than doing the online backup.

Hustler 9 posts Joined 12/15
05 Jul 2016

Thank you both for clearing up.
Regarding archive loggs:
Is there anyway we could run both FASTLOAD AND Backups parallely on the same objects?
         Trouble is DBC needs to take archive logg on the objects( during online backups) it supposed to backup; however if FASTLOAD is running a load job then it takes explicit archive log and then DBC skipping objects which lead to BACKUPS COMPLETED WITH ERROS. Is there anyway to go around this.
If Above is a NO,What if we make sure FASTLOAD is running exclusively after the Backup job? While backup job continues, if the FASTLOAD is kicked off; will it go to blocked state or fails?


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