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will there be a dataloss doing rebuild index instead of reorg index?

Posted on 2010-09-21
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Hi All,
will there be a dataloss doing rebuild index instead of reorg index?
if not, then what is teh use of prefering reorg instead of rebuild?
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Question by:saratcm
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Scott Pletcher earned 500 total points
ID: 33730097
No, SQL will never allow a data loss with any command.

Which is preferred actually depends on the condition of the index(es).  [If there are no indexes, neither rebuild nor reorg apply at all anyway.]

If the index is only slightly fragmented, say from 10-30% [you will see some recommendations as low as 20%, or as high as 40%], then you can do a reorg.  A reorg is always done live, so the table can be used by others while it is being reorg'ed.  The reorg is done is small chunks and so does not have a major impact on log size either.  A reorg does not fully defragment the index but it does some logical defragmentation.

Conversely, a rebuild of a clus index requires SQL to lock the table until the operation is complete [unless you have the Enterprise version, specify ONLINE rebuild, and meet the criteria for an ONLINE rebuild].  But a rebuild completely rebuilds the index, restoring the FILLFACTOR and removing all unrequired pages (if, for example, lots of rows have been deleted).

Rebuilding a nonclustered index also requires a table lock unless you specify ONLINE; the table will be locked while the nonclus index is being rebuilt.

"Locked" means any row mods (insert/update/delete) are prevented for sure, as are column mods.  

I don't think you can even read the table, not even if you specify WITH (NOLOCK), but I'm not 100% sure of that.
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