Why is the sort operator needed in this plan
The sort is spilling on multiple passes turning an optimization attempt into a bit of a horror. Fix the cardinality estimate coming from the seek – it is far too low right now, causing the spill. You do not want a magic trace flag to turn off the sort optimization – fix the underlying cause.
The residual predicate on the seek, and the nasty predicates in the Filter immediately after are always going to be a cardinality estimation nightmare. It's only 240K rows; materialize the set in a temporary table.
Edit: Based on the additional information in the comments, there are two things you can do:
- If the 'best' plan is fixed, force the plan you want with a plan guide. If you cannot find a parameter value to avoid the sort, manually remove it from the XML show plan and use that to apply a plan guide.
- If all else fails, generate a plan with TF 8738. This will remove the pre-lookup sort optimization.
I think it might allow read-aheads on the lookup. I can't find the read-ahead statistics in the PE output to guess.