Oracle Scratchpad

August 24, 2010

Index rebuilds

Filed under: Index Rebuilds,Indexing,Infrastructure,Performance — Jonathan Lewis @ 6:56 pm BST Aug 24,2010

A couple of years ago I wrote about a poster on the OTN db forum who was puzzled by the fact that when he started rebuilding tables they got bigger.  (Bad luck, sometimes that’s what happens !)

A few days ago a related question appeared: I rebuilt some indexes and my query got slower. (Bad luck, sometimes that’s what happens – again!)

If you rebuild an index it’s physically different and its statistics are different. Plans can change and go slower because the index stats look sufficiently different; plans can stay the same and go slower because the index is physically different. 

I’ve added a couple of comments to the thread – there may still be some further mileage in it.

[Further reading on rebuilding indexes]

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