One index of one my databases has the strange behaviour of getting slower after time goes by.
Even though my maintenance plan includes a 'Rebuild index' step on all user databases. After a while it gets so slow that my entire application/server grids to a halt.
But when I do a manual rebuild on the particular index, the query time is brought down from minutes to half a second.
Why does the 'rebuild index' step of the maintenance plan seem to skip this index, and why does it work manually? (the maintenance plan runs correctly without errors, every night)