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Dropping indexes


Dropping indexes

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Jagadish Kumar Punnapu
Jagadish Kumar Punnapu
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Comments posted to this topic are about the item Dropping indexes
PRAMANA.DBA
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Good Question..
Carlo Romagnano
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PRR.DB (1/1/2014)
Good Question..

+1
:-)
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Good One!

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steve.jacobs
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Really good question. Had to think about that one for a second :-D. Of course, I was thinking more into your question like "what if there are relational keys associated or referencing foreign keys?" which of course would throw errors.

Again, thanks.
Raghavendra Mudugal
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Good one, thank you for the post. Smile

(even though, I got it right with inconsistent thought on this "This may take significant time on large tables." and was wondering if the DB is online and users connected to it via application and the application performance would reduce in that particular time frame - and then thought; wait - why would they drop index on the main DB, such activity is done on mainly DWH in the maintenance window with very less users connected and the impact would be very less... and then thought may be this was the case of 2008 R2 and below and may be 2012 and 14 have bettered in this area.... well!!!)

ww; Raghu
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Thomas Abraham
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Got it wrong as I was using http://technet.microsoft.com/en-us/library/ms176118.aspx as a reference and it says, in part:

If a clustered index is dropped by using MOVE TO, any nonclustered indexes on the base table are rebuilt, but they remain in their original filegroups or partition schemes. If the base table is moved to a different filegroup or partition scheme, the nonclustered indexes are not moved to coincide with the new location of the base table (heap). Therefore, even if the nonclustered indexes were previously aligned with the clustered index, they might no longer be aligned with the heap.


which would appear to contradict the given answer.

What am I missing here?

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george sibbald
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Thomas Abraham (1/2/2014)
Got it wrong as I was using http://technet.microsoft.com/en-us/library/ms176118.aspx as a reference and it says, in part:

If a clustered index is dropped by using MOVE TO, any nonclustered indexes on the base table are rebuilt, but they remain in their original filegroups or partition schemes. If the base table is moved to a different filegroup or partition scheme, the nonclustered indexes are not moved to coincide with the new location of the base table (heap). Therefore, even if the nonclustered indexes were previously aligned with the clustered index, they might no longer be aligned with the heap.


which would appear to contradict the given answer.

What am I missing here?


non-clustered indexes also contain the clustered index column(s) to identify the location of the actual rows to retrieve data from. If the clustered index is dropped then the non-clustered indexes have to be rebuilt to remove the clustered index and replace it with row ID information

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Thomas Abraham
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george sibbald (1/2/2014)
Thomas Abraham (1/2/2014)
Got it wrong as I was using http://technet.microsoft.com/en-us/library/ms176118.aspx as a reference and it says, in part:

If a clustered index is dropped by using MOVE TO, any nonclustered indexes on the base table are rebuilt, but they remain in their original filegroups or partition schemes. If the base table is moved to a different filegroup or partition scheme, the nonclustered indexes are not moved to coincide with the new location of the base table (heap). Therefore, even if the nonclustered indexes were previously aligned with the clustered index, they might no longer be aligned with the heap.


which would appear to contradict the given answer.

What am I missing here?


non-clustered indexes also contain the clustered index column(s) to identify the location of the actual rows to retrieve data from. If the clustered index is dropped then the non-clustered indexes have to be rebuilt to remove the clustered index and replace it with row ID information


I understand that part. However, the reference seemed to imply that the non-clustered indexes had to be MANUALLY rebuilt, IF the table was moved to a different filegroup or partition scheme.

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george sibbald
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I would read that If as an 'as well'. This is because the clustered index is still being dropped, but the data is moved at the same time, but is now a heap.

Best details on when non-clustered indexes get rebuilt here

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