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Compatibility level 80 Vs 90 - SQL Server 2005 Expand / Collapse
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Posted Friday, April 1, 2011 7:55 AM
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Hi,

Some of the people that work with me on the company convert a database from SQL Server 2000 to SQL Server 2005 without even changing the comaptibility level.

They just do backup on SQL Server 2000 and restore the database on SQL Server 2005.

I always change the compatibility level to 90 and change the error detection from torn page detection to CheckSum.

I would like to tell them why is good for them to change the database compatibily level to 90, but i am not choore. I know that if the database is in compatibility level 80 it works in backword compatibility level, but that affects the performance of the database or can cause any damage?


Thank you
Post #1087471
Posted Friday, April 1, 2011 8:21 AM
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Having converted many databases from SQL2000 via backup and restore and running on SQL2005, changing compatablility is relatively low on my scale of things that need to be changed. I have a mixed bag of compatablilties on my production 2005 boxes and the ones set at compatablity 80 vs 90 perform no differently.

The reason we didn't change them is due to some of the older 3rd party tools they were utilizing. We didn't want to break anything, and once you change the compatiblity you cannot go back.

I agree about the checksum change. That would be higher on the priority list to be changed.
Post #1087495
Posted Friday, April 1, 2011 8:25 AM
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"I agree about the checksum change. That would be higher on the priority list to be changed"

but you can only change the to checksum if you are in compatibility level 90?
Post #1087500
Posted Friday, April 1, 2011 8:34 AM
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You can change the Page_verify_option to Checksum on compatibility 80 without going to 90

SELECT name, create_date, compatibility_level,user_access_desc,state_desc, recovery_model_desc,page_verify_option_desc FROM sys.databases

This is just a quick way to gather that info for you
Post #1087504
Posted Friday, April 1, 2011 8:41 AM
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I would never automaically change the compatability level ot 90 after an upgrade as there is too big a risk that some application will fail to function in Level 90.

Test first, then change the level if required.
Post #1087513
Posted Friday, April 1, 2011 8:45 AM
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" would never automaically change the compatability level ot 90 after an upgrade "

I would never too...

The database will be tested with the app
Post #1087518
Posted Friday, April 1, 2011 1:32 PM
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Lowry Kozlowski (4/1/2011)
We didn't want to break anything, and once you change the compatiblity you cannot go back.


The compatibility level can be changed back, if needed. When you change this, there is nothing in the database that is upgraded or converted that will prevent you from changing it back.

All this does it tell SQL Server what commands, functions, etc... are available in that database.


Jeffrey Williams
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Post #1087685
Posted Thursday, January 17, 2013 1:35 PM
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The compatibility level can be changed back, if needed. When you change this, there is nothing in the database that is upgraded or converted that will prevent you from changing it back.

All this does it tell SQL Server what commands, functions, etc... are available in that database.

That's not *all* it does. It can change the parsing of queries, their execution plans, and the meaning of certain constructs in queries. It can change sort orders. There's a lot it can cause to happen--but you're right, it doesn't change the data.

I in particular have experienced seeing an application negatively affected by an ordering issue when changing the compatibility level to higher. That the application relied on a particular order without an ORDER BY was poor design; but nonetheless it existed.
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