Question

I am having quite a difficult time at finding why adding an index on the foreign key of a table is slowing down the view of my colleague. This view is composed of several packed views with outer join and inner join. I tried to remove them one by one to figure out where the problem was, but I cannot say, it doesn’t seem to come from a particular view but more from them all.

I knew indexes could slow down insert or that they were taking size on the hard drive, but I never read anywhere that they could be responsible for slowing down a view. The truth is when I do :

DBCC FREEPROCCACHE
DBCC DROPCLEANBUFFERS
GO

select top 20 * from  MyView

It takes 20 seconds with the index and 9 without.

CREATE NONCLUSTERED INDEX [IX_MyField] ON [dbo].MyTable
(
    [MyField] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, 
  IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON,
  ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY]

Answer 1

It’s possible your OTHER indexes or stats are out of date. If they aren’t current, it’s possible the query analyzer is choosing a sub-optimal execution plan using your new index since it thinks that will be quicker.

Try running:

UPDATE STATISTICS WITH (FULLSCAN)

on your table.