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The Effect of Reindexing on a backup file Expand / Collapse
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Posted Thursday, December 12, 2013 4:48 AM
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Hello,

I am trying to find out the impact of a database reindex on an SQL Server backup.

The scenario is as follows:

I have a database called ABC that I perform a backup of to a flat file using the command in a SQL Agent job - BACKUP DATABASE ABC TO DISK = 'C:\Backups\ABC.DAT' WITH INIT

Now I perform some defragging of indexes in the database using REBUILDS for those with a fragmentation over 30% and a REBUILD for over 10%.
The database remains in FULL mode while this is running.

Once complete I perform another backup of the database to a flat file using the same method as before - BACKUP DATABASE ABC TO DISK = 'C:\Backups\ABC.DAT' WITH INIT in a SQL Agent job.

What I would like to know is if the data held within the backup file has changed its order?

Regards,
Steve



Post #1522237
Posted Thursday, December 12, 2013 4:49 AM


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Very likely.

Why?



Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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Post #1522238
Posted Thursday, December 12, 2013 4:56 AM
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Hi Gail,

Thank you for the speedy reply.

The reason for the question is because I am having a debate with my EMC backup admins about the unique data the backups present to our Data Domain nightly. I am of the view that once we defrag the indexes and perform the backup again to a file the blocks in the file have moved around, so they will be seen as unique by the data domain which uses deduplication.

Hope I am making sense.

Post #1522240
Posted Thursday, December 12, 2013 5:19 AM


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Depends how big the blocks that the dedupe looks at, but yes, probably they will have changed. This is not a good reason to not rebuild indexes


Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1522247
Posted Thursday, December 12, 2013 5:31 AM
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Hi Gail,

I have not intention to stop the rebuilding of the indexes.
Just trying to help the EMC team work out what is causing the growth as the data domain seems to be a black box even to them.

It is running low on space.


Regards,
Steve
Post #1522250
Posted Thursday, December 12, 2013 5:32 AM
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Hi Gail,

Do you have expereince of working with Data Domains and deduplication?

Regards,
Steve
Post #1522251
Posted Thursday, December 12, 2013 6:59 AM


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Only in the 'black box' sense.


Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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Post #1522291
Posted Thursday, December 12, 2013 7:05 AM
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OK
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